Full spectrum light

'Full spectrum' lights (FS) are often reported in the media as being necessary to treat SAD. We wanted to clarify what FS means. They are termed full spectrum because the energy is not limited to the visual waveband (in other words they also deliver a little ultra-violet, UV), and because the spread of colours is more complete than with normal fluorescent tubes

When Dr Rosenthal first worked on SAD and light therapy he theorised that a lack of daylight was the problem so he decided to re-create daylight as closely as he knew how and therefore used FS lamps. These early trials were successful and, for a short while, it was thought that FS lamps were necessary to treat SAD. Since then however, Dr Rosenthal and others have done a lot of work to see what is important about the light. The conclusion is that any bright white light is helpful (recent findings suggest one part of the spectrum around 470nm green-blue may be the most important) but that UV light is not necessary and for the sake of caution should be avoided. Compared to our standard lamps FS lights do produce slightly truer colours, but they do produce less light and will take longer to use. Simply changing the lamps in a room to FS type will not increase the light levels sufficiently to treat SAD.

Pharos lightboxes are virtually full spectrum because they have an excellent spread of colours (Ra88), much better than a normal fluorescent tube (Ra60) and traditional full spectrum lamps with the UV light measure Ra92. So we like to think we have the best compromise of excellent quality light without any unnecessary risk.

In his book Winter Blues, Dr Rosenthal wrote ‘In our early studies we used lights that [were intended to] imitate the balance of colours found in sunlight - so called full spectrum light. Researchers have no evidence that such light is any better than ordinary white fluorescent light. In fact [these lamps] were designed to emit more Ultraviolet (UV) rays than regular fluorescents ... Their potentially harmful effects are a distinct disadvantage… Be sure that any fixture you purchase includes ... ultraviolet reducing features.

Is full spectrum light always bad?
Not at all. It's just that when you need to be close to very bright light, as with a lightbox, other types are preferable. Even better than full spectrum are Solux bulbs, the truest daylight bulb ever made.

Morning full spectrum vs. cool white light in Seasonal Affective Disorder
SLTBR Abstracts. 1989 June
Patients were treated with 2 hours of morning light, either full spectrum or cool white, in a randomised double blind crossover fashion for 6 weeks. The two treatments were equally effective in reducing and/or eliminating SAD symptoms.

Dr. N Rosenthal (who first described SAD and light treatment) said in May 1992 "There is no justification for including ultra violet light".

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