Comments on “YOU NEED MORE LUX”

Full Bridge Rectifiers

J 2016-11-23

I see some reasonable-looking luxmeters on amazon for <$20, so you might consider getting one, for science! Also, I’m a big fan of full bridge rectifiers, but high power linear power supplies require great big transformers, and 300W 24V transformers tend to be more expensive than the switching supplies you bought. (And you’re right you’d need a huge rectifier as well as a huge smoothing cap). A better option for people working on the cheap might be used PC power supplies, which often have 12V rails in the tens of amps.

Light hacks

Rob MacLachlan 2016-11-23

That’s a great find. I got inspired by your earlier post and got parts for a 100W (actual power) LED box, along the lines I had suggested, using current drive LED strips. But your solution is both cheap, nicely packaged, cost effective, and doesn’t use high voltage.

You do have to take care that most LED lights are advertised as “incandescent equivalent watts”, rather than actual physical LED watts. That’s almost universal for AC fixtures or replacement lamps. Given the discussion below of “LED watts” marketing term below, my guess is is that your actually input power is probably 1/2 that or less. Note that they are also quoting “LED lumens”, which I would assume would mean the light output if driven at the theoretical max. You can pretty easily find the actual input power by measuring the DC current and voltage. Is each bar really drawing 12.5A at 24V?

What is the difference between “LED Watts” and “True Watts”?

LED diodes are rated based on the amount of power (wattage) they can theoretically handle, if they are perfectly cooled. Excessive heat causes LEDs to degrade (“burn out”) and makes them shift the color of light they are giving off, so in the real world LEDs are never run at their full rated wattage. This means that “LED Watts” is a completely useless number for comparing the light output from two different lights– for example, you can have two “500 LED Watt” lights, with one running 100 watts of actual power through the LEDs, and the other running 300 watts of actual power.

Ignorant when it comes to electronics

David Chapman 2016-11-23

I failed my graduate oral qualifying exam because the examining committee asked me about capacitors. I had, obviously, only the vaguest idea of what one does.

At the next department meeting, the faculty as a whole un-failed me (and, the rumor mill said, informally failed the committee) because, as a CS student, I wasn’t supposed to know what a capacitor does. I’m not quite sure why the committee didn’t know that, and so asked me about capacitors instead of the Schönhage–Strassen algorithm.

@J —Thanks, I’ve added a link to your comment from the post!

@Rob — ” Is each bar really drawing 12.5A at 24V?” Hmm, I don’t know. The fixtures seem to have internal voltage regulation (since they are designed to run on 12VDC but will take up to 30). They do claim 30k lm; if that is true, then they’d have to actually draw about 300W. (LED luminous efficacy is ~100lm/W.)

Very nice. I was looking into

gwern 2016-11-25

Very nice. I was looking into LED shop lights for similar reasons and to save floor space (I thought it would be nice if I could get rid of my old broken torch lamp with the giant CFLs), and also saw the car lights, but the electrical wiring killed them for me. Big LED tubes + shop lights might be a better way for people not confident in their electrician skills.

500W light bar

Adam 2016-11-30

I found this:
It was $55.59 when I bought it, $60 now. Says it’s 500W 50,000 lumen.
I also got a 12v 500W power supply for $35 off amazon. I’m going to hang it directly over my computer desk. I hope the power supply is high enough, I’ll be running it at max. Did your 300w supplies drawing 300w all the time have any issues?

500W FTW!

David Chapman 2016-11-30

Nice find! The only 500W ones I could find on Amazon were quite a bit more expensive.

The power supplies I got are fine. I was afraid they might get hot, but the internal fans are more than adequate; they’re not more than a little warm.

The light bars themselves have massive heat sinks, but still get quite hot. Borderline of too hot touch—OK briefly but would get painful after a few seconds.

Actual power draw

Adam 2016-11-30

So, I was reading all the comments from the first blog entry. I saw the one about the LED strip not actually drawing all the wattage it says it should and the reply link to

There it suggests that since it’s for a car, it might expect the 12v voltage to actually be ~14v like a battery would provide. I was wondering if that might be the case with these as well. If you have a multi-meter handy, could you check if your 300W lights are actually drawing 300W off the power supply?

Actual power draw

David Chapman 2016-11-30

My $12 multimeter only goes to 125 mA. I’m not sure how to measure serious DC wattage; if anyone does know, and it’s inexpensive, I will try, because I’m curious too.

The LED bars I got apparently have an internal voltage regulator / power supply, because they will accept anything between 10V and 30V. LED strips, by contrast, are just bare LEDs wired together in clear plastic.

So, my best guess is that this issue with LED strips does not apply to the bars—but I could be entirely wrong.


Adam 2016-11-30

Just googled it. What’s needed is a shunt.
It’s put inline on the live wire and scales down the high amperage to the mA range. As long as what it steps it down to is lower than what your meter can handle, it’ll work. There are 50A -> 75mA shunts on Amazon for ~$6
I’d probably have had to figure that anyway when I went to measure mine once I get it, good to know! 50A multimeters are $$

Using a shunt

David Chapman 2016-11-30

Thank you! I will probably do this, eventually… I’m unusually busy at the moment, so it may not be for a few weeks.


Rob MacLachlan 2016-12-01

David: yes, a light bar with a wide-range input like yours definitely has an internal switching power supply to convert the input to constant output current. r.e. using an external shunt, it’s a resistor, so you get volts out for current in. 75 mV @ 50 A means it’s a 1.5 e-3 Ohm resistor.

Disclaimer: for some reason I find thermal design interesting, and I tend to end up designing things that run cooler than they really need to.

If the external heat sink is getting that hot, then the LEDs are probably running hot enough that they aren’t going to last 50,000 hours. This is a reasonable tradeoff for the original intended use. No matter how cool it seems, I doubt that many people who buy these are going to run them all that much without really pissing people off. Also, on a vehicle at night it’s likely to be cooler than indoors and there will be some forced air cooling due to vehicle motion. If you were to aim even a pretty small fan in the direction of the lights, it could make a big difference in the operating temperature.

BTW, for high-power LEDs, end-of-life is conventionally defined as output less than 70% of rating. As well as long term output degradation, higher operating temp also produces a temporary output reduction, which is typically 10-20% as long as the rated max operating temp is not exceeded. Higher temp also tends to shift the color temperature in the blue direction.

In the LED strip datasheets I was looking at, light output was quoted at a hotspot temp of 50C, and life at 70C. To touch, that’s the difference between “hot” and “bloody hot”. Depends on your finger, but here’s one calibration:
>I vaguely remember an engineer mentioning an old rule of thumb
> for quickly estimating temperatures on circuit boards: you put
> your finger on a component, and it went something like this:
> Feels cool … 25 to 35 deg C
> Neutral … 37
> Warm … 40 to 50
> Very warm … 50 to 60
> Hot … 70
> Makes a blister… 100 and up
> Does anybody have the numbers that go in here?
>I added some above. For most folks, 70 is about as hot as one can stand for a second or two (does depend on calluses, though).

There’s no way of knowing how much hotter the LEDs are than the heat sink, but we can be confident they are hotter.

r.e. StackExchange comments about “12V” strips, most of those comments seem on point too. Drawing less than rated power at 12.0V makes sense from both marketing and engineering perspectives. On the marketing side, there seems to be a lot of spec creep, and you have to compete. On the engineering side, there is the issue of 13.4V vehicle operation and just generally providing a margin to improve reliability (derating). Most customers aren’t going to notice if it draws less than rated power, but are going to notice if it blows out or runs so hot that it smells like burning plastic.

r.e. power supplies. If you buy enclosed switching power supplies off of EBAY then you’ll probably end up with a power supply that is rated reasonably conservatively, and should run fine at 100% of rated output. I’ve been pretty happy with EBAY as a source for cut-rate Chinese electronics; the next notch up might be Jameco, which stocks “Mean Well”, a low-cost brand with a decent reputation.

500w power supply?

Adam 2016-12-01

Hmm, I got this one:
It doesn’t say it’s switching or universally regulating or anything.

Should I have gone for something like: ? (though shipping time on that is way long)


David Chapman 2016-12-01

If the external heat sink is getting that hot, then the LEDs are probably running hot enough that they aren’t going to last 50,000 hours. This is a reasonable tradeoff for the original intended use. No matter how cool it seems, I doubt that many people who buy these are going to run them all that much without really pissing people off. Also, on a vehicle at night it’s likely to be cooler than indoors and there will be some forced air cooling due to vehicle motion.

That makes sense! Does seem like they may have limited lifetime, then.

It doesn’t say it’s switching or universally regulating or anything.

I’m reasonably sure it is, and not to worry. (But, I don’t know anything about electronics. Rob would know better.)

Power supplies

Rob MacLachlan 2016-12-02

Almost all power supplies are switching these days. Universal input just means you can operate on 120 and 240 VAC. As long as you are in the US, the one you got is fine.

I referred to David’s bar as having wide-range input because it was spec’d to work over 12-24V or an even wider range. That would be unreasonable for LEDs without some sort of internal current regulation. And at these power levels, a switching converter is the only sane option.

Sean van Gessel 2016-12-03

Outdoor floodlights

David Chapman 2016-12-03

Thanks! Yes, outdoor floodlight of this general sort are a plausible alternative. The best lumens/$$ ratio I was able to find a couple months ago was this one—which is actually a pair of 30,000 lumen floods. You can buy more than two at a time, but not only one, of that particular model, for some reason.

Before Rob’s most recent message, I would have said that the bars were a better bet, in terms of cost and ease of use, but if those are going to have a lifetime problem, the floods may be the way to go. Presumably they are designed to last, since they’re meant for lighting parking lots and such.

So, got my light all wired up

Adam 2016-12-06

So, got my light all wired up, still need to hang it once I find a ladder.

Using the lux meter on my phone I measured 100,000 lux from ~12in away, and 10,000+ lux at 5ft! So I’m pretty happy with it so far :D

Reliability, lifetime, etc.

Rob MacLachlan 2016-12-06

It’s really the wild west with LED lighting right now, both because things are moving so fast, and also because far east suppliers are eagerly selling whatever seems to sell, without worrying much about the long term. For me, for light therapy, it isn’t a disaster if it fades after a year or two.

The one concern that I do have with the flood lights or light bars is in how you use them for light therapy. With the light box, you are supposed to frequently glance directly at the light. I’m not sure that is such a good idea for extremely bright sources, but if they are bright enough, you may not need to do that. Yes, sun light is quite bright, but you don’t stare at the sun. If you have a 100k lux flood light, that’s your sun. What you might want to do is make sure you have some white surfaces in your work area that get brightly lit.

From wikipedia Daylight:
120,000 lux Brightest sunlight
111,000 lux Bright sunlight
20,000 lux Shade illuminated by entire clear blue sky, midday
1,000 - 2,000 lux Typical overcast day, midday
<200 lux Extreme of darkest storm clouds, midday
400 lux Sunrise or sunset on a clear day (ambient illumination).
40 lux Fully overcast, sunset/sunrise
<1 lux Extreme of darkest storm clouds, sunset/rise

Reflective diffusing surface

Rob MacLachlan 2016-12-06

Note also that diffuse reflection is still directional. You’ll get the most reflected light if you are viewing the surface at right angles vs. a more oblique view. You should be able to get a sense of this with the phone lux meter.


Jolly 2016-12-09

If you wanted to vary output lumens, what would be the easiest way to put a dimmer switch on the lightbar?


David Chapman 2016-12-09

Most LED lighting systems are not dimmable, unfortunately. You can assume they are not unless they say they are. These bars don’t say they are, so they almost certainly aren’t.

If you get several, you can turn some off.

So what would happen if you

Jolly 2016-12-10

So what would happen if you took that 500W lightbar and used a powersupply that only output 12v, 250watt?


Jolly 2016-12-16

Installed one of the 500watt light bars that Adam linked to. It’s not as bright as I would have thought, but I have it currently aimed up at the ceiling.

Also this power supply is NOISY. I’m going to have to replace it with a computer psu with larger/quieter fan, or I’ll have to work wearing earplugs all the time.

Silent power!

Jolly 2016-12-30

I found an virtually silent power supply - (at least up to 500w)
1) Buy an HP Platinum 1200W platinum efficiency power supply - such as the DPS-1200FB-1 A. You know it’s platinum because it has the blue plug socket. Example -
Then buy an adapter to use it like (You could DYI, but I’d rather just buy an adapter).

Virtually silent at 500watt draw! (This could power up to 900watt at 120ac, 1200w at 240, but no idea how quiet that might be) It’s also really small. 10x6x2, including the adapter board.

Blessed silence

David Chapman 2016-12-30

Oh, excellent! The ones I got are pretty noisy. I’ll be tempted to upgrade!

Worrying info about retina damage

Alex 2017-01-05

Heads-up: there’s a study from the NIH linking LED lighting to macular degeneration. The experiment used “cold” (>4500K) and bright (>= 6,000 lux) light, meaning most people probably don’t need to worry and get rid of all their LED lights, but this seems like one application where it would be a cause for concern.

Macular degeneration

David Chapman 2017-01-05

Thank you for the heads-up! Definitely a matter of possible concern.

There’s extensive discussion of this paper on Hacker News. (Thanks to Daniel Klein for pointing this out to me.) Here are some thoughts… bear in mind that I’m utterly non-expert on any of the relevant science.

There’s weak evidence that blue light is key for SAD treatment; and weak evidence that blue light causes macular degeneration (in general, not just from LEDs). So this might be awful, in the long run.

The evidence for blue light causing macular degeneration in humans seems to be sketchy:

The main observation from HN is that even the brightest SAD lights (such as the ones I’ve built) are less bright than winter sunlight, and have pretty close to the same spectrum. That suggests that exposure to white SAD lights is probably no worse than going outdoors on a sunny day in winter. (Eye doctors do recommend that people with early-stage macular degeneration wear blue-blocking sunglasses when going outdoors. However, the evidence for this seems to be doubtful currently. UV is definitely a risk, but in humans blue light is not so clear. The clearest risk factors for macular degeneration are actually the same as for the “metabolic syndrome” diseases such as diabetes. Losing weight is good for you.)

The “daylight” LED spectrum is not exactly the same as sunlight, and it’s possible that the difference is critical. But this seems relatively unlikely to me.

Another observation is that this study was done in rats, which tend to avoid sunlight, and whose eyes, some other studies suggest, are much more prone to light damage. Further, they found that LEDs were particularly bad for albino rats (whose eyes are abnormal anyway), and that fluorescents were worse for non-albino lab rats. Humans are probably more like non-albino rats, so the upshot might be “bright light is bad for your eyes,” and sunlight is the brightest light, so you are probably no worse off with a SAD lamp than if you lived in a subtropical locale and got enough sun.

I’m not sure what to make of this, for now. I would recommend not looking directly into bright SAD lights. It is probably better to avoid blue-only SAD lamps. It may be worth experimenting with using “warm white” lights rather than “daylight” ones—although my weak guess from experience is that warm light is less effective for SAD treatment. If you have early-stage macular degeneration, or know or suspect you are particularly at risk, avoid bright LEDs, or at least consult a retina doctor first.


David Chapman 2017-01-05

Hmm, albino humans also have serious problems with bright light, due to lacking normal protective pigment in the retina:

So, I would add to my list of super-tentative recommendations that you avoid SAD phototherapy if you are albino.

Or a lab rat.

Thank you for this article.

Peter 2017-01-16

Thank you for this article. One question: Do the led strips give off UV light? And if so, what is your thinking around that? Seems like there is a common sentiment that UV light should be avoided in SAD treatment lights. I haven’t dove into any research on that though, so it’s more a curious question.

Thank you!

LEDs and UV

David Chapman 2017-01-16

Thanks, that’s an excellent question!

Normal LEDs emit very little UV—less than any other type of artificial light. (And much less than sunlight, of course.) It’s not zero, but it’s close.

In the past few years, specialized UV-emitting LEDs have been developed for UV-specific applications; but they are expensive and wouldn’t show up in any ordinary LED lamp or bulb.

Fluorescent lights generate a lot of UV. Ones intended for general lighting include a filter to eliminate most of it. However, some “full-spectrum” and especially “grow light” florescent bulbs deliberately allow UV through. Those should not be used in SAD lamps.

The "500w" light bar I bought

Jolly 2017-02-17

The “500w” light bar I bought (same as adam linked) only actually draws 140 watts from the wall (measured via a killawatt meter, before the ac-dc conversion)

Only 140W

David Chapman 2017-02-17

Wow, that’s disappointing!

Are kilowatt meters inexpensive? I’m tempted to check mine.

Do you have any subjective report on whether the bar has helped with SAD?

January and February have been quite unusually dark where I live (most overcast on record, I believe). I haven’t been depressed, but my focus and productivity have been poor. I do think the lights help (because I’m not depressed, and not entirely paralyzed, and because there’s a sense of relief as soon as I turn them on). But, it’s totally possible I’m fooling myself!

I have “900W” in the three bars I’m running, and have definitely been tempted to add more.

AC power meters

Rob MacLachlan 2017-02-20

Not expensive. You can buy for maybe $40 at home store, for home energy efficiency surveys. Kill-a-watt is one brand.


Luminous flux

Daniel P 2017-03-11

Where are you getting the luminous flux rating of 30,000?

The Amazon product details list it as 13,200 lm. Or is it 13,200 lm at 10 V, rather than at 30 V?

Product switcheroo, and lm/watt

David Chapman 2017-03-12

Whoa… The product I bought was the WoneNice 300W 30,000lm bar, which had the Amazon ID B01M1FV2DA. That’s what my Amazon order list still shows. (Screenshot here for the record.) Amazon is redirecting that to product ID B016LTDPLO, the Tenviii 32” 180w 13,200lm bar. (I’m not sure if this is a screw-up or a scam.) I’ve updated the post to reflect this.

When I wrote the post, all the auto light bars advertised around 100lm per watt. Rob and others above expressed skepticism about this, and it looks like they were right. Most are now rated around 60-70lm/watt. So, the 300W bars are now advertised at 17,000 to 22,000 lm.

Either they were lying before, and got forced into the update, or it may be that (as Rob also suggested) the lights were running too hot, and they’ve decreased the internal voltage (and light output) to increase their lifespan.


Baers 2017-04-03

First off thank you for starting this blog. I read both the corn bulb post and this one regarding the LED bars. It is really relieving to see that other people are also suffering from SAD, and are actively looking to find a solution to it. In the past few years I’ve become more aware of the symptoms and now am almost certain I suffer from SAD. Initially I thought my cognition just slowed down in the winter time compared to spring/summer, but it extends to so much more. My drive, my outlook, disposition, demeanor, concentration are all so drastically different in the colder/darker months than the warmer/brighter months, and I have serious issues with sleep in the winter (insomnia and crazy night anxiety), all of which basically go away when sunlight is at a certain strength. I do notice a bigger impact when the UV is at higher number (late march - september), but am very curious to see if I can see improvement without UV exposure with these LED bars.
Just had a few questions/comments:
1. Amazon now has 30,000 lm led bars - so it looks like they switched back from the previous 13,200 they had tied to that original link.
2. I read that these light bars aren’t drawing the full 300 watts from the power source - is it possible to power these with just two 300 watt power sources?
3. I’m so unfamiliar with these power sources - so after I order and receive them - is it pretty straightforward how to set them up? Do they plug into anything or are they self contained power sources that just run out over time?

Any clarification on some of the above would be GREATLY appreciated. Thanks David for creating this webpage, can’t tell you how good it is to find other people who have to deal with this.

Power supplies

David Chapman 2017-04-03

Yup, SAD definitely sucks!

We don’t currently know how much power the bars actually draw. You could try using less power than they are rated for, to see if it works. Or, they are inexpensive enough that maybe it’s not worth experimenting.

The power supplies plug into the wall. However, the ones I got don’t come with a power cord. If you are completely unfamiliar with wiring, you might want to get help to hook them up. If you know how to use wire strippers (the only tool needed), it will be straightforward.

For each power supply, you will need a power cord with a plug. The simplest way to get that is to buy an extension cord from any hardware store, and cut off the “female” plug end. Leave the “male” end to plug into the wall. You strip the insulation off the bare ends of the wire and stick them in the input side of power supply. Then there are screws you tighten so they don’t fall out.

The light bars have a cord coming off them with two wires inside. You can cut it to length, strip some insulation off the end of the two wires, and connect that to the output of the power supply.

Received all equipment just need to set it up

Eric 2017-04-16

Thanks for the explanation David. Most of it makes sense, but unfortunately I am unfamiliar in this space and calling myself an amateur with this type of equipment would be an understatement. With that said, on the power supply the “input” is the L&N (labeled A/C) on the left side of the power supply, correct. Also what voltage should I be setting the power supply at, I’m assuming the 110v it is set at is ok. The other larger power supply I have is preset with no option to adjust at 100-120. The bars have a chord coming off of them but it is pretty short, with a red and a black wire. There is also a separate cord that came with each light bar that is extremely long, the light bars red and black cord I believe connect with the red and black wires from the longer cord and I believe on the other end of the cord there are red and black rings which probably are where you connect in a vehicle. There is a third piece that sticks out of the longer cord that looks almost like the female end of an extension cord but has four inserts and the insert size is very thin… I have no idea what this is for was hoping this could somehow just connect the lights directly to the wall (bypassing the power supply) but I’m guessing that’s not its purpose.

Any advice would be great. Thanks

Wiring it up

David Chapman 2017-04-16

on the power supply the “input” is the L&N (labeled A/C) on the left side of the power supply, correct.

Yes; but actually there are three power input connections. You should use three-wire power cord with a three-prong plug. The third input is “ground,” labeled with a symbol that has several parallel horizontal lines. “L” is “line” and “N” is “neutral.”

So which is which on your power cord? Different countries have different ways of labeling them, and some countries have several. If you are in the US, line will be black, neutral is white, and ground either green or bare (no color). Sometimes they aren’t color coded, but instead the neutral wire has a rib or groove in the plastic insulation around it, and then usually the ground will be middle of the three wires.

If you are in the US, then plug power is 100-120V, and you should set the power supply for that.

The bars have a cord coming off of them but it is pretty short, with a red and a black wire.

Here the red wire is positive (+ voltage) and the black one is negative (- voltage). You should connect those to the +V and -V outputs of the power supply. (One of my power supplies has the negative output labelled COM.)

The other long wire thing is specifically for auto use, and not helpful for your purposes.

LED Light Panel

EricE 2017-09-11

I was thinking of making this for photography:

But now I may make a couple and chase off the wintertime blues with them!

External floodlights better than light bars?

Ben Redelings 2017-09-29

Another source of high-lumen light sources seems to be external floodlights, like this one:
These have square chips that provide 5000 lumens @ 50 watts per chip. You can find lights from Laputa and Morsen that have up to 12 chips, thus providing about 60,000 lumens.
These lights all have heat sinks built in.

It seems that the advertising for the light bars is usually misleading. Usually if it says its a 300W light bar, then it is actually a 100W light bar that is “300W equivalent”.

I have a 150W LEPOWER flood sitting on some shelves – it comes with a standard AC plug, so there is no need to get a power supply. The 600W lights also seem not to need a power supply; they plug into a junction box.

I’d be interested in any comments on these.

External floodlights

David Chapman 2017-09-30

This does look very good!

I guess “how hot does it get?” would be my only consideration. The heat sinks look small for the job. If you mount them in a way to avoids any fire hazard, this seems like it would be a great solution.

I’ve recently started using the light bars again, after not needing them for several months. I think that (as Rob suggested above) they’re probably somewhat dimmer and blue-er than when I bought them. However, it’s hard to be sure, because it’s been a year, and I couldn’t measure their output accurately then.

External Floodlights

Ben Redelings 2017-10-19

I measured the heat sink fins on the back, and the hottest part was about 150F. The side is probably around 130F, or maybe lower. I used a “heat gun” that you point at the thing and read the temperature, I think from an IR sensor.

DYI 60K Lumen lamp.

Adrian Elizondo 2017-10-30


David Chapman 2017-10-30

Thanks, Ben! Offhand, 150F seems cool enough not to be a fire hazard (but I don’t know anything about that, don’t take my word for it!)

I’ve now measured the temperature of my lightbars. The heat sink on one of them is at 125F; the other two are at 145F. The first is significantly cooler to the touch, so this isn’t a measurement artifact.

The cooler one is run off a different power supply than the other two.

Rob, do you have any insight into whether a power supply difference could cause this temperature difference, and if so what the difference might be?

Adrian —Wow, crazy, man!

+1 to LED floodlights. Add a diffuser!

David 2018-01-10

LED floodlights seem to be a great alternative to the commercial SAD boxes which are less powerful and usually don’t even achieve 10k lux from 12” away.

I just got a 150W / 11000 lumen LEPOWER ($60), cut out & attached a square of LED diffuser plastic to the glass front. Still waiting for a lux meter to get exact measurements, but my phone’s ambient light sensor says 10k lux from 18” away.

Yes, adding a diffuser will reduce lux, as it is by definition spreading the light’s direction, and this sheet has ~65% transmittance. However, diffusion is necessary not just for comfort but also for safety. Damage is not caused by lux or illuminance (lux == lumens/m^2 coming from all directions), but rather by the apparent size of the area these lumens originate from (lumens per solid angle, at your eye). A laser puts out low lumens but from a tiny emitter, but appears to be a tiny point source, focusing to a single point on the retina, potentially causing damage. Similarly, you want to avoid being able to directly see the emitter chips which emit a lot of light from a small area.

From High-Power LEDs Pose Safety Hazards:
“Because the emitting region is small (3 mm^2 in the case of the Luxeon K2, for example), the eye can focus the light to form a small image on the retina with a high power density capable of causing localized damage.”

Heat Concerns Require In-Air Mounting?

JJ 2018-01-22

Are these hung from chains for heat-related purposes? Could they in theory be placed directly on a wall? What makes for sufficient heat consideration in positioning?

Mounting on the wall

David Chapman 2018-01-27

I think mounting on the wall would probably be OK. The hardware on the ones I got would stand the bar off from the wall by about an inch, and they don’t get all that hot. But, I’m not at all an expert on fire safety, so I could be totally wrong!

(Sorry to be slow to reply; I’ve gotten badly behind on responding to site comments due to a cold that wiped me out for a couple of weeks.)

Bar lights for SAD

Mary Anne 2018-08-21

I have been reading all the posts and threads you have in dealing with seasonal affective disorder (I suffer miserably in winter).

I have absolutely NO electrical skills, and so don’t understand about how to create the lamps, or get the auto lights to work in my home. So I ask you this, at Home Depot, there is a vast variety of construction LED “work lights.” Some are battery, and some are plug in ones in tall stands, and most come in super high intensities of brightness. Would these work? Could I just use those (rather then the commercial “sad lights”), and would I have to worry about color temperature, or skin cancer? I just need something fast, affordable, and I am not knowledgeable or know anyone who knows technical stuff.

"Work lights" a/k/a "shop lights"

David Chapman 2018-08-21

These may now be a good choice!

LED versions didn’t yet exist when I wrote this post. (At that time, they used halogen bulbs, which were effective for SAD but got very hot, which made them burn out in a few weeks, and also was a fire hazard.)

LEDs won’t cause cancer (because they produce almost no ultraviolet light).

As far as I can tell, color temperature is less important than just “very bright.” Unless you have a choice of different ones, it’s probably fine to ignore it.

while the wombat confused me slightly, thanks for working on SAD

Barbara 2018-08-27

I found your blog while searching for light boxes to buy, clutching in my hot little hand my August birthday gift money from my older sister, who compassionately (and passionately) wants to save me from another terrible winter. 2017 was the worst! Even though I had a job, AND health insurance, AND a loving family, and even a new dog in the family… AND is even snowed on Christmas Eve. Nothing was happy. Ugh. I live with men and women who can build things, and they own power tools, so we’ll be going for the LED light bars. If you don’t mind explaining–the wombat confused me. I wonder– are you living in the Pacific Northwest up from Down Under? not that it makes any difference where you are living during the short days, but the short days in Portland and Seattle can be uber-grey. I know that the rain grows the trees, and I love the green, so I just want to be able to make it through the winters because I can’t imagine living anyplace else. thanks!

Wombat optional

David Chapman 2018-08-28

The wombat is just a joke… He’s my wife’s favorite plush toy.

We’ve escaped to Tasmania winter sun a couple times, though, and saw wombats there, and maybe he does remind us of that!

I’ve never lived in the Pacific Northwest, but it’s famous for gray, yeah. Sorry to hear about 2017—I hope the LEDs will help some this year!

LED light bars

Mary Anne 2018-08-28

I also know how “to build things,” and own, use several power tools. However, it is not clear on how to hook these lights up in a home. I have no knowledge of electrical skills, and many people do not either.

If someone could lead me to a link on what to purchase, and how to convert the LED light bars into a home I would appreciate it. Even a licensed electrician, who works in homes, can refuse to wire a project like this.

$126.84. 20,000 to 60,000 lumens 3000k bright white-no wiring

Kirk 2018-09-09

No special wiring required.

My setup should produce 20,000 to 60,000 lumens Light appearance: 3000K bright white
without any wiring required & cost
(ON SALE)$44.64 (5X(4packs)$8.19)+tax
90-Watt Equivalent PAR38 Non-Dimmable Flood LED Light Bulb Bright White (4-Pack)

Confusing whether it’s 1000 or 3000 lumens

$82.20 (4 floor lamps @$19 each+tax)
4 Walmart floor lamps holding 5 bulbs each.(hopefully Led flood lights will fit without modifications)
Mainstays 5-light Floor Lamp

Each bulb should consume about 15 watts. So 15 watts X 20 lights is 300 watts which should easily work hooked into one power strip & one outlet. For reference some of my computer bitcoin mining equipment runs at 1,300 watts with not too much problem on one outlet.

Plan to blast the light for 30 minutes when I wake up working out on my total gym.

Any thoughts/feedback/questions appreciated.

Many LED flood bulbs

David Chapman 2018-09-10

This looks like a plausible solution!

If you can find similar bulbs at a higher color temperature (5000k or so), that might be better. (But, evidence for the importance of color temperature is pretty thin.)

enjoyed it

Michael 2018-09-23

Very interesting. thanks for writing it up.

Follow up.

Kirk 2018-10-03

I finished putting together my lights.

272 watts Power @the wall.

Measuring lux using lux meter android app
211,880 lux (meter maxed) extremely close to one flood light.
7,000 lux sitting close
3,000 lux from my Total gym.
80,000 lux putting phone up to one flood light.


David Chapman 2018-10-04

Thanks, great to have these numbers!

The dramatic differences illustrate how important it is to get really close to the light and/or for it to be really powerful. Many of the commercial solutions advertise “10,000 lux,” but that’s quite meaningless without a distance measure. And, some of them are only as bright as a 100W incandescent, which is barely better than nothing (and which you can get for a tenth the cost of the fancy box).


mmortal03 2018-10-04


How do you have the four floor lamps arranged? Are they all pointing directly at your Total Gym?

“3,000 lux from my Total gym.”

I know this thread is talking about SAD, but as far as people with delayed circadian rhythms, I’ve read elsewhere that a person should be getting about 10,000 lux for at least 30 minutes as soon as he or she wakes up, or 2,500 lux for at least 2 hours.

I wonder how directly the research on combating SAD matches the research on people trying to entrain their circadian rhythms.


Kirk 2018-10-10

They are probably 4 feet from total gym.

I work shift so I could see this helping me get going.

I only used 3 of the 4. The gf ended up with one.

One thing that is a bit of a pain. The flood lights are heavier than normal bulbs. So the base isn’t heavy enough to keep lamps stable on ground. so i leaned them against furniture.

The lamps have bendable arms so can adjust any way you wish.

Still been fairly nice in my area weather wise.

LED lighting choices

chad golden 2018-10-22

Was looking in Amazon for LED lighting. Saw 500w, 800w, 1000w outdoor floodlights. Here is a 1000w unit.

Thoughts? And would a diffuser be recommended?

I was considering these as an alternative to SUV light bars. such as these

Guess I could gang 8 of them together!

Outdoor floodlights

David Chapman 2018-10-22

Powerful LED floodlights are new since I wrote this post, and look like they may be the best current solution.

We discussed them recently here.

A 1000W unit will generate as much heat as a 1000W room heater, so you’d want to be careful to mount it in a way that avoids fire risk.

It would be intense—which is good!—but you won’t want to look directly at it. Since it’s described as a flood, hopefully it spreads the light somehow itself. (It’s not obvious to me how that would work from looking at it.) A diffuser would do the job if not; you’d need to find one that could withstand the heat.

If you go this route, please let us know how it goes!


jacob 2019-04-11

Hi - thanks for your article on SAD light therapy. Wondering if you have any updates/comments on how your system has been working out for you? I’m wondering if I have this SAD affecting me after this winter and considering a build for next winter. Thanks.

Hack for SAD Light therapy

Suzanne 2019-04-16

Yes, thank you, David, for illuminating this subject of light therapy and the need for more lumens! I am looking for an easy effective therapy to try. I, like Jacob, would like to request an update as of April 2019. It would be great if you could do a round up of the latest greatest solutions for someone that just wants to plug the light into the surge protector and be done. Thank you!!!

SAD light update

David Chapman 2019-04-16

I’m still using both the lightbars and the portable system I built the previous year. They have made a big difference for me. They don’t completely reverse SAD, but do keep me functional during the winter.

Some individual LEDs in the lightbars are starting to die. I think they probably run too hot (as commenters suggested). They’ve lasted three winters of heavy use, so that’s not bad. However, there are probably better alternatives now.

Specifically, outdoor LED floodlights (which were not available when I wrote this post in 2016) run on 110V so you can just plug them in. They are meant for long-term industrial use, so they ought to be reliable. However, Amazon reviews suggest that some are, but some die after a few months, so that’s something to look out for. Also, they do produce a lot of heat, so you need to mount them in some way that avoids fire hazard.

I haven’t tried the outdoor floods, because the lightbars are still working for me. As more LEDs die in them, I’ll probably replace the lightbars with floods next winter.

If anyone has experience with the flood lamps, or other solutions, it would be great to hear!

Nomadism = SAD solution

remedios 2019-04-17

Despite my best interventions, SAD hit me hard this year, pretty much obliterating my good thinking and good moods in February and March.

There may be a silver lining: all of us SAD sufferers have an opportunity to abandon our oppressive homes-from-the-Victorian-age and follow the paths of our native american predecessors.

We can literally follow their paths, dragging our tinyhomes behind us while we migrate from the Northwest to the Southwest seasonally, or move from Boston to Tennessee for the winters. We can live on the coasts in the summers and retreat to made-of-glass longhouses in sunny meadows for winter songs and fasting.

Benefits: We get to take 2 road trips per year, no more SAD symptoms, lower heating and cooling costs, the chance to drive our electric vehicles with the tow packages, plus we get relief from some autoimmune conditions, and we can all go to where the other fluid people are.

Granted, this may be like using a halberd to kill a fly. But: we’d probably be amused. And maybe literally less seasonally affected!

Colour Temperature

Caribbean Sun 2019-07-22

Hi All
I’m surprised you don’t try to replicate a WARM sun rather than DAYLIGHT in terms of colour temperature (*Kelvin)
A warm sun is surely better than a colder normal daylight sun ???
I’d be tempted to make my own ‘light bars’ using WARM white LEDs - or is it more about UV or IR ????
Or intensity during the fullness of winter ????

SAD lights, fun with LEDs

M. Pobop 2020-04-21

I have a light bar similar to these, but it started to flicker annoyingly within a few months. I kept it on the floor beside my bed on a timer, so it would wake me up in the morning and I’d just stare at it (at first with eyes closed) to start the process of getting up from the bed.

So I bought some 50 watt COB LEDs from aliexpress for less than 2 dollars each. Surprisingly, when I measured them, they turned out to really be 50-watt LEDs. So that’s dirt cheap. They require no power supply, and can be fed straight AC from the wall, which is crazy as well.

The catch is that unlike the light bars, these don’t come with the heat sink, which turns out to be the expensive part. The leds for a 1000W Led array would cost about ~1.6$ per 50W led = 32 bucks money $. Assuming 50% efficiency, that’s 500 watts of heat that need to be moved somewhere. I’m currently thinking about how to solve this.
I tried fixing one of these LEDs to a piece of aluminum and it gets hot enough to fry eggs on within a few minutes. Luckily SAD lights are mostly used during the colder months, so maybe they subtract from the heating costs.

Thanks for the articles, they’ve been very helpful and fun to read.

How do you not go Blind?

Jonathon Wisnoski 2020-11-12

Trying to research these SAD lights, but it is so confusing to me. sunlight is bight, that is why you never allow it to even be in your peripheral vision or you go blind. Even 60 watt equivalent lights, you never look at, and 100 actual Watt LEDs are placed 50 feet up and you always keep your back to them.

Also, are LEDs just always safe for UV? I was under the impression UV control was an important aspect of SAD lamps?

One last question. What is the benefit of having a sad lamp you use for therapy, vs just upping the wattage of your house lights? Could I not just replace all the 40-60 equivalent LEDS in my house for 100+? would this passive light for hours and hours not be more beneficial?

A "budget-friendlier" option

Charlie A. 2021-01-25

First, thanks so much for sharing your experiences with SAD and light therapy – I’ve found it incredibly helpful.

I took a shot at getting 10k - 15k lux at 3 feet for around $50 (US). After a a lot of poking around on Amazon, I ordered these:

They are a pair of plug-n-play LED flood lights rated at 100W/each, and the pair cost me $55 US on Amazon. My photometer reads about 12,000 lux at 3 feet, with only modest heat dissipation from either unit. After a week of owning them, my preliminary report is nearly 100% positive. The brackets on the back are sturdy and provide a number of different mounting options – and could be particularly good for a mobile set-up. The thick tempered glass, and powder-coated aluminum body / heat-sink appears to be tough enough for use as a work light (and it’s IP 66 rated for water-resistance). Sorry for the commercial, but wanted to share the information in hopes it might help someone else!

How you like the pair of $55 dollar lights?

Chris 2021-01-28

Any noticable difference with SAD yet?

re: approximating your lux exposure

Heather Pihl 2021-09-29

I don’t know if you did yet, but I would suggest buying a light meter. It’s worth it! I did some research with it years ago, and my technique was to hold the meter sensor next to my eye, facing the same direction, to figure out how much lux my eyes received.

I wrote about my research in a book I wrote specifically for Seattle (free to preview and also download at

Imperceptible Flicker From LEDs potentially damaging to health

Sean 2021-11-13

Hi David,

love your two articles about constructing an LED SAD lighting rig to emulate sunshine in the winter.

One issue I would like to pick up on though (which I’ve only just myself discovered) is the potential dangers of flickering from LEDs.

Just about all artificial lights flicker to varying degrees. The most stable appear to be incandescent, whilst the worst offenders are LEDs and fluorescents. The flickering is imperceptible to the human eye but is still registered subconsciously by the brain.

You can test the flickering by holding your phone camera (or any other digital camera) up to the light. It will be alarmingly obvious.

There have now been numerous studies showing that the flickering of the LEDs can lead to a range of health issues such as seizures, migraines, stress etc.

Here area couple of links to published studies:[Ra1]_F(KM)_PF1(AJ_SHU)_PFA(SL)_PN(SL).pdf

I’m curious to know what your thoughts are on this. Have you noticed any effects yourself? I’m thinking perhaps using flicker-free LEDs is the solution?

Light colour and waveform

SusanC 2021-11-13

My understanding was that it’s the amount of light that matters, and the exact colour of the light or how delivered (light is vs whole room lighting) doesn’t matter too much.

But, possibly, the variation of light over the day matters. The working hypothesis here is that there’s some kind of phase locked loop in your brain that normally gets synced to the daily solar cycle, but in winter gets desynced, to bad effect.

If want you’re doing with the light source is to provide a clock signal that will be followed by a bio”fickle phase locked loop, the waveform (brightness over 24 hours) possibly matters.


David Chapman 2021-11-14

Thanks, this was an issue I hadn’t heard about before. I read both articles, not super carefully. It appeared that the worst outcome would be headaches and eye fatigue, and there is actually no data supporting that possibility, so it’s not something I will worry about personally. YMMV!

You can test the flickering by holding your phone camera (or any other digital camera) up to the light. It will be alarmingly obvious.

I did this with several of the bright LEDs I have around the house and didn’t see any flickering.

(It’s often obvious visually with fluorescent bulbs, though, which I don’t like.)

My light box

SusanC 2021-11-16

For what it’s worth, I have started using my light box this week.

Last winter was extremely unpleasant … daylight deprivation + total social isolation due to covid19 lockdown (xmas got cancelled at the last minute in UK) plus unknown risk level of catching new variant of (moderately) deadly disease…

Flicker Experience

Paul K. 2021-11-28

I tried those “GLORIOUS-LIGHT” bulbs that Charlie A. posted above, and while they are very bright and have a sturdy mount, they flicker intensely. For me it creates a deeply “creepy” effect. An amazon reviewer commented that noticeable flickering is common in cheap LEDs. So I’m returning them and looking a little further upmarket (and also for bulbs with better CRI – color rendering index, a measure of how truly it renders colors, on account of having a more or less full spectrum).

Daylight Simulation

David 2021-12-03

It makes sense to think of lighting technology as simulation of sunlight. If we acknowledge that light affects and triggers physiological processes in our bodies, then the treatment becomes one not of pills and chemicals, rather more holistic; for example, no one denies that ultraviolet light is fundamental for the metabolism and health of plants and reptiles.

Proper indoor lighting may have to mimic all the aspects of sunlight—from intensity to spectrum and variation during the day—to avoid conditions like SAD and D-vitamin deficit with metabolism and immune disorders. Until then, we have LED arrays and tanning beds.

re: light therapy as adjunct to sunlight

Heather Pihl 2021-12-03

I agree about thinking of lighting technology as simulation of sunlight. I think it can be a little tricky to get it right. I continue to experiment with it. I have a 10,000 lux light box (since 1996, and it’s maybe my favorite light therapy), light earbuds from Humancharger (formerly Valkee), green light glasses, colored glasses for outdoors, and then spending an extended time outside. It’s a topic of great interest to me, so much so that I wrote a book about it a few years ago (full preview is open, so you can read it or else download the e-book):

I think the indoor lighting standards are insufficient for our health and need to be revisited. Or, a light therapy room needs to be provided for people in the workplace.

How to use the floodlight

Amit Gulab Deshwar 2021-12-25

Hi David,
For the Solla floodight you linked to, how are you using it?
Are you pointing it against a wall, or suspending it and pointing it at you?


David Chapman 2021-12-25

Hi, I have posted a picture here. It’s in a large living room that has exposed rafters, and I screwed it to one of those. The bottom of the light is 6‘4” above the floor, and the bottom of the rafter is about eight feet up (same height as a normal ceiling). I have it at a diagonal to the coffee table I’m working at and pointing sideways. I can see the panel out of the corner of my eyes, but it’s not pointing straight at them.

Pointing straight at you might be too bright, but would probably be OK if it’s several feet away and above your line of sight. I wouldn’t recommend looking straight at it for more than a second or so.

In a small room, bouncing it off a white wall in front of you would probably work well, but I haven’t tried that.

Daylight Simulation

David 2022-01-05

It makes sense to think of lighting technology as simulation of sunlight. If we acknowledge that light affects and triggers physiological processes in our bodies, then the treatment becomes one not of pills and chemicals, rather more holistic; for example, no one denies that ultraviolet light is fundamental for the metabolism and health of plants and reptiles.

Proper indoor lighting may have to mimic all the aspects of sunlight—from intensity to spectrum and variation during the day—to avoid conditions like SAD and D-vitamin deficit with metabolism and immune disorders. Until then, we have LED arrays and tanning beds.


Tim Martin 2022-01-13

Thanks so much for your blog posts on lumenators! Any chance you could post a picture of the floodlight in your living area? From the amazon pictures it looks SO bright… I’m just kinda concerned about it being too much.


David Chapman 2022-01-13

Hi, yes, there’s a picture and explanation here. It’s hard to tell from a photo how bright something is, because cameras adjust image exposure automatically, but this gives some sense. In this large room, the lamp is not painfully or unpleasantly bright. It might be, in a small room; I don’t know.

LED light strips for shop daylighting

Heather Pihl 2022-01-13

I encountered a shop owner the other day who had changed her lighting two months ago to LED lighting. It’s a drycleaners. All her lights were overhead fluorescent lights previously, and now those have been changed out with exclusively LED light strips/bars(?), maybe 4000 or 4500K. I have never been in such a bright shop, ever! I asked her how she is sleeping at night and she said she doesn’t sleep long. She did say that she has energy when she leaves work at 6:30, no longer tired. I was so surprised by how bright it was (maybe too much so). Is this a trend in shop lighting, does anyone know? Usually the problem is the reverse - too little lighting and people don’t feel so well. Sorry if this is the wrong place to post my comments.

What wattage for Solla Light?

Amr 2022-09-02


The link for the Solla Flood Light you linked above has many different wattages. Which one did you order? I’d like to try this out for SAD.

600W, for a large livingroom

David Chapman 2022-09-02

I got the 600W one. It’s great for a large, otherwise poorly-lit livingroom. It would probably be overkill for most rooms.


Amr 2022-09-02

Thanks so much for your response David. I’ve battled SAD for decades and I never liked the idea of having a light a foot from my face. It never felt natural. I’m going to try your solution instead and would love your advice.

I work from home and my office is north-facing so it doesn’t get much sunlight. The dimensions are 14ft x 13ft. Their is a large opening opposite from my desk to our dining room, and the wall above the opening is where I’d like to mount one of these stadium lights. That would put it at about 45 degree angle above my seated position, and about 10 ft away from my face.

What wattage would be appropriate for the space?

Also, ddid you wire yours into your home wiring or did you attach plug outlets to them? I’d like to put mine on a smart outlet as well, so they are only on in the morning for just as long as I need to treat the SAD.

Have you found anything else to work for SAD? I was convinced taking Vitamin D supplements would help, and I think maybe they did, but the scientific evidence for it is conflicting.

14ft x 13ft

David Chapman 2022-09-02

Well… I don’t know. Very little about light therapy for SAD has solid scientific evidence, unfortunately, except that it does work.

“Too much light” has never been a problem for me personally, and 600W is not going to make your room brighter than the outdoors in summer.

If there’s room for two lights there, I guess you could try a ?400W? and add another ?200W? if it seems like you’d want more.

I’ve just now noticed that they how have dimmable versions. Also, it’s nice to switch from daylight-white to warm-white in the evening. So if you get two, something like this one might be a good choice for the second.

They come with bare wires; I attached that to a plug, and plugged it into a heavy-duty extension cord with a switch on it.

I’m skeptical about vitamin D as a SAD treatment; but as you say there’s evidence both ways. I haven’t found anything else that works, unfortunately.

It's winter again...

SusanC 2022-11-11

Right now, I have terrible Seasonal Affective Disorder. The lightbox helps a bit.

So far so good

Amr 2022-11-11

So far I’ve been using the 600 watt stadium light for 45 minutes in the morning and it seems to be working.

Susan C, the light boxes you can buy for SAD are underpowered. You might want to try the solution in this article, using an LED stadium light.

Twitters a titanic anyway

Liz C. 2022-12-20

Hi! Love your new amendment for the newer sad light!

I fail at twitter; would you terribly consider adding your instructions here for your stadium light setup?

By the looks of it I’m considering putting it in the corner of the living/dining; or against the same wall as the windows it has, so as to mimic the current sunlight in the setting. It looks like a very bright light. Can you work next to it, like you have the straps set up here? Hard to tell as a twitter drop-out :):)

Disregard anyway

Liz C. 2022-12-20

You might as well disregard my last comment; I’m finding all your recent comments have it going on!

What using LED work lamps?

Wilson Cheung 2023-01-05

I’m reading your article in 2023 now several years later. I was about to follow your guidance to build my own super bright LED lamp. Then I noticed Amazon sells very bright LED work lamps on stands. I don’t think any of them was as bright as the 48000 lumen lamp you were proposing using but they came with tripod stands and AC plug. So it’s a lot less work. I’m currently trying out a 20000 lumen work lamp.

For those of us not inclined to have to build our own power supply and wire up our own cord I’m curious what do you think about the LED work lamps.

Answer to Questions

Marko 2023-11-23

“What happens for you when it’s been a few overcast winter days in a row, and then suddenly the sun comes out early one afternoon? “

It doesn’t make a difference to me.

“In winter, do you turn on all the lights, even when you don’t need them to see what you are doing? And maybe housemates wonder why? And maybe you secretly wish there were a few more lights you could put on?”

No. Actually, I like a dim ambient light in my room.

“Do you try to fly somewhere sunny for as much winter vacation as you can get, every year? When you first step outside at your destination, do you feel an immediate sense of enjoyment and relief?”

I don’t actually try to fly to somewhere sunny, but when I do get a break, it does feel really good.

Liking a dim ambient light

David Chapman 2023-11-23

Yup! As a footnote in the post said, this is also common. Bright light supplementation is definitely not for everyone, and apparently not for you.

Not exactly

Marko 2023-11-23

Well, though I said that, I actually do like the idea for the health benefits during a dreary winter. Today I have my ceiling light on, and I am expecting to get the corn bulb stuff set up tomorrow because I have ordered it. I am not sure about if I will stick with it though, because I have already tried a really crappy method: buying a $5 plant-grow bulb from the hardware store and putting it in a desk lamp. It does work, but I have experienced problems like losing the veracity of reality at work. Like, I process something a certain way, and then see that it was wrong later. That got better once I stopped, but on the other hand being in a dim room or the dark ends up making me feel totally listless, so I’m trying the corn bulbs.