Light bulbs, blue rays and melatonin

A bunch of folks who are much smarter than me have proved a link between blue spectrum light (i.e. light in the 460 to 480 nm range) and the body's melatonin production. Melatonin is a hormone that (inter alia) makes you sleepy. This knowledge is especially helpful to people suffering from insomnia or circadian rhythm disorders.

In short, exposure to "normal" light (i.e. white light, which is not actually white, but contains all the colours of the rainbow) to some extent inhibits the production of melatonin. This is because white light contains light in the blue spectrum. In some people, such exposure to blue rays will make it difficult for them to fall asleep, perhaps because of an oversensitivity to light. Conversely, reducing such exposure increases the body's melatonin production.

Turning off the light would be one solution - albeit an impractical one. Another solution would be buying a pair of glasses with amber filters that block out blue rays (much like sunglasses that block out UV-rays). A third and perhaps more viable solution, would be to employ light bulbs containing no blue light.

Light bulb companies don't typically include information on which wavelengths of light their bulbs emit. An ordinary bulb emits white light (including blue rays). Even a coloured, non-blue bulb may emit some blue rays. So how can our hapless insomniac decide which bulb to use?

The answer is simple. Buy a coloured bulb and analyze its light. This is much easier and cheaper than it sounds, and you don't even have to be as much of a nerd as I am.

All you need is a prism. A prism splits light in into its constituent spectral colors. When white light enters a prism it is split up into the colours of the rainbow. But if the source light contains no blue rays, the prism will output all the colours of the rainbow except blue.

Nobody, however, seems to own a prism these days. Don't worry. Everybody owns at least one compact disc and CDs work just as well.

Take a look at the below image. I've tested three different light bulbs: A 28W halogen bulb, a 40W yellow bulb and an 40W orange bulb. The coloured bulbs were manufactured by the same company and differ only in terms of colour. The same camera settings were used for all three pictures (no flash, 1/4 second shutter speed, F 4.5) and pictures were taken in a room with no other light sources.

CD Prism

Just by looking at the CD prism you can easily determine, which bulb emits the most blue rays. As a quasi-scientific touch, I've employed image analysis (histogram information) to determine the amount of blue in each image.

Image analysis seems to confirm what we have already established visually. The halogen bulb emits lots of blue rays (and thus may inhibit melatonin production), the yellow bulb less and the orange bulb the least. All of the bulbs emit at least some blue rays.

So in this test, the orange bulb takes victory (although it definitely isn't easy on the eyes).

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