What's the Best Indoor Light?

I recently replaced my incandescent bulbs with energy-saving fluorescents. But a friend told me that the ‘cool white’ spectrum of light they produce can actually be bad for us; and that full-spectrum light, such as what plant lights give off, is healthiest. True?

– June 27, 2011

First, full-spectrum light is not the same as the light given off by grow lights used for plants. I personally prefer full-spectrum light to other types of artificial light because I like the way it looks, but while researching your question, I found that "full-spectrum" is a marketing term, not a technical one.  

Full-spectrum light bulbs are supposed to provide light that resembles natural daylight, which manufacturers claim, explicitly or implicitly, is healthier than ordinary artificial light. These products can cost several times as much as those that have identical lighting effects but are not identified as full-spectrum.

According to investigators at the Lighting Research Center (LRC) at Rensselaer Polytechnic Institute, full-spectrum light won’t affect health in ways different from other electric light sources. They note that research has shown that while our sleep/wake cycle is strongly regulated by the solar light/dark cycle, "other activities including mental awareness, mood, and perhaps even the effectiveness of the immune system go through regular daily patterns" and that exposure to light is the most important environmental stimulus for regulating these circadian cycles and synchronizing them to the solar day. The LPC experts said that short wavelength (blue) light is the type that is particularly effective in influencing our physiology.

This means that to maximize efficiency in affecting the circadian system, the LPC researchers said that a light source should not mimic a full spectrum, but instead should maximize only short wavelengths, which are at the blue end of the visible spectrum. Even if a full-spectrum light source includes short wavelength light, "it will not necessarily ensure proper circadian regulation because, in addition, the proper intensity, timing, and duration of the light exposure are all equally important . . ."

Full-spectrum lights may offer some psychological benefits, according to the LPC experts, but no biophysical explanation for any positive effect has been found.

Since no adverse health effects have been linked to indoor lighting, I wouldn’t worry about your fluorescent fixtures. You’ll do more good for your health by making an effort to get some direct sunlight as often as possible (given climatic conditions in your area), not only to optimize your body’s production of vitamin D, but also to boost your mood and normalize your sleep/wake cycle. (You should also be sure to sleep in complete darkness.)

Andrew Weil, M.D.

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