Comment by DenisM | Hacker News Reader

Comment by DenisM | Hacker News Reader

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A related anecdote:

I dabbled in light therapy and found the first lamp I tried [1] very effective. However I have also started receiving comments from my colleagues about my nice new facial tan, in the dead of winter. I freaked out because the lamp was in my field of view 30 minutes per day every day without any eye protection, and sent the lamp back to where I bought it. Subsequently I have tried three different LED-based lamps and they seem to have no effect. I have carefully measured the light output and placed myself at proper distance to get the requisite 10,000 lux in all cases. No dice.

Here's the kicker - that lamp [1] appears to be the one used in some of the light therapy research (that's why I got it). It is entirely possible that much of light-therapy research was contaminated by badly designed lamps. There is no FDA certification for any of this as far as I know.

[1] Carex Day-Light Classic Plus Bright Light Therapy Lamp. Supposedly UV-filtered.

How is a Vitamin D lamp supposed to promote the creation of Vitamin D without UV?

It only blocks most of the UV. The lamp itself is blasting a very intense amount of light, so that the circadian-sensitive mechanisms in your eyes are fooled into thinking you're outside on a bright summer day. The vitamin D is secondary to the main function of the lamp, which is to be incredibly bright in comparison to most indoor lights. The light-therapy lamp must be aimed at the eyes (even for blind people!). It just doesn't work as well if you can't see it directly. You would have to pump even more light into the room to get the same amount reflected off of other surfaces.

Also, the lamp could be putting out UVA and not much UVB, so it could tan without producing much vitamin D.

For just the vitamin D, I'd get a "5.0" UVB lamp in a bare-bulb fixture, designed and sold for indoor avian and reptile pets. Aim at arms and hands, and away from the eyes. They're about $15 per bulb, and should be replaced every 6 months, as the UVB output degrades over time. Afterward, they work perfectly fine as compact fluorescents, behind glass or under lampshades, for several more months, albeit shaped inconveniently for some fixtures.

A "10.0" bulb is for desert-species pets. The UV output is too high for the overall lamp brightness, and may damage your eyesight, as human pupils don't constrict enough. I suppose you could wear sunglasses, but that seems counterproductive to just buying a lower-UV lamp.

These "light therapy" lamps don't. They just supposedly improve mood from the exposure to bright light itself and don't claim to produce vitamin D.

LED lamps do not emit any UV unless you specifically order ones that do. Fluorescent lamps put out more UV by comparison!

Do LED lamps not produce light via blackbody radiation? If they do then they must produce at least some UV

> Do LED lamps not produce light via blackbody radiation?

I'm pretty sure the answer to that is that they do not.

No, they use electroluminescence, not incandescence.

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