MORE LUX: light bars for SAD

LED lighting is improving rapidly. You can install very bright lights for treating seasonal affective disorder (SAD) easily and inexpensively. Common sense says that will be more effective than commercial SAD lights that are much less bright. My experience confirms this.

This post explains how to use LED light bars to create a 90,000 lumen sunlight simulator—as shown above.

You need MORE LUX! More lumens too

Lux measure how much light you get. The sun at noon on a cloudless day in summer provides about 100,000 lux; an overcast day in winter is about 2,000 lux. SAD seems to be largely caused by getting less light in winter, so getting a decent fraction of 100,000 lux seems ideal.

I say seems because research so far has not fully explained how seasonal depression works, nor how best to treat it. I summarized some of that research in a previous post on LED SAD lights. Bright light phototherapy is definitely proven to improve SAD symptoms, but some details are unclear—including how much light is optimal.

Most SAD light therapy research was done with 10,000 lux, because that was the brightest that was practical using fluorescent bulbs, which were the best lighting technology available at the time. There’s nothing magic about this number. My personal experience is that much more than 10,000 is better.¹ LED lamps can be much brighter than fluorescents, so you can get well over 10,000 lux.

In contrast, most commercial SAD light boxes claim 10,000 lux, but provide much less in practice. A claim of lux, by itself, is meaningless, because it depends on how close you are. The further you are from a lamp, the less light you get. At a realistic distance, most light boxes deliver around 2,000 lux—the same as a gloomy overcast sky in winter. In my experience, that is not effective.

Lumens measure how bright a lamp itself is—how much light it produces. How much light you get depends on how bright the lamp is and how much of it is aimed in your direction and how far from it you are.

Most light boxes produce 3,000 lumens or less; with that brightness, you won’t get 10,000 lux unless you put the lamp a few inches from your eyes. (So the “10,000 lux” claim skates close to false advertising.)

The best-selling SAD light on Amazon is brighter than many, at about 3,000 lumens.² It claims 10,000 lux, but—like nearly all commercial products—does not say at what distance. Calculations suggest you’d have to have your eyes less than a foot from it. That is awkward and uncomfortable and the glare may be unpleasant.³

A few years ago, before I started building my own SAD lamps, I bought the brightest light box I could find.⁴ It produces 17,200 lumens—much more than most. I found it only modestly effective when working between one and two feet from it.

This year, I assembled a set-up with three light bars rated at 30,000 lumen each—90,000 lumens total. I don’t know exactly how much light this delivers to my eyes, but it’s much more than 10,000 lux. (Details on brightness below.)

I find it much more pleasant to use than a light box, and it is plenty bright enough to be effective.

Construction

These light bars are designed for off-road SUV driving at night. They have the lowest cost per lumen of any practical lighting source I could find this year. (They are dramatically less expensive than the “corn bulbs” I used in the desk-top SAD lamp I built last year.)

I bought three at $42 each. LEDs produce 100 lumens per watt; these are 300 watts each. [Update, March 2017: the product I bought is no longer available. This one seems to be closely equivalent, and is $45 currently. It seem likely that these bars actually produce around 20,000 lumens, not the 30,000 they claim; see discussion in the comments.] You can get similar light bars at different wattages, up to at least 500W; when I was shopping, 300W was the sweet spot for cost per lumen.

Although they are meant to be attached to a jeep, they look quite good indoors. Or, at least, they look a lot better than my 2015 desktop lamp! Depending on your decor and aesthetic sense, your opinion may vary.

Conveniently, they have locking, rotating mounting hardware at each end, so you can orient them at any angle you like. I slanted mine so they are at about a 60 degree angle above me.

Since they are designed for automotive use, they run on 12V DC, and you can’t just plug them into a wall outlet. I got one of these 300W 12V power supplies ($19) and one of these 600W ones ($55).

So, my total cost was about $215 counting the chains, hooks, and wire I bought at a hardware store. That’s about the same as commercial SAD light boxes that put out 10% as much light.

Those power supplies are overkill for the job; they are meant for electronics, and so regulate their output to within a small fraction of a volt. The light bars will accept anything from 10 to 30 volts, so you could build yourself a quick-and-dirty power supply for much less money if you have basic electronic skills. You’d want a fuse, a transformer, and a FULL BRIDGE RECTIFIER. Plus maybe a smoothing capacitor; but I’m not sure you need that. [Disclaimer: I don’t know anything about electronics, don’t listen to me.]

Subjective experience

I’m really happy with this set-up. It is much more comfortable to use than a light box.

The desktop SAD lamp I built last year produces 30,000 lumens. I found it effective when used at a distance of two feet; on really dark days, I would pull it still closer. It is, however, pretty unpleasant. The light is at eye level and the glare is intense. It feels unnatural, partly because there are pools of darkness all around it.

Light from the light bars arrives from an angle above, which both decreases glare dramatically and feels more like sunlight. It illuminates a broader area, so there’s less sense that you are sitting in the dark with a bright light shining only on your face. Subjectively, the experience seems much more natural.

The light bars each have 100 LEDs, each of which sits inside a reflective cup. Most of those are shaped to send most of the light light in a single direction, as spotlights; I aimed them to point at my eyes when working in the beanbag chair. (The nearest bar is four feet from my eyes; the furthest is six.) Some of the cups are less focussed, giving a flood effect, providing some illumination to the surrounding area.

The horizontal bars of light do still seem somewhat unnatural. I think a very bright single-point flood source (using an HMI bulb perhaps) would feel better.

There’s some evidence that blue light, simulating a clear sky, is particularly helpful for SAD. I’m considering mounting blue LED strips on the ceiling next to the bars.

So far, I’ve found the light bars fully effective against SAD, in late November, when I generally found myself slow and stupid without treatment. However, the worst symptoms typically arrive in January, and I can’t yet say definitively how well they work then. [Update: I was not depressed; however, I was not very productive, due to lack of focus. Subjectively, I’d say that the system was highly, but not fully, effective.]

How bright is it?

I’d like to be able to tell you how many lux I receive when sitting working under the bars, but I can’t give a precise number.⁵ My estimate, based on calculations, measurements, and subjective experience, is about 25,000.

• It’s much brighter than the 17,000 lumen light box, even at one foot from that.
• It’s somewhat less bright than midday sun on a cloudless day in October in northern California, but not much less.
• It is brighter than last year’s desktop lamp when two feet from that, but not quite as bright as at one foot.

In short: it’s very bright, and with much less glare than a light box.