Science Questions

How do full spectrum bulbs prevent seasonal affective disorder?

Sun, 6th Jul 2008

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Colin Donnelly asked:

How do full spectrum bulbs prevent seasonal affective disorder?




We put this question to Professor Russell Foster:

Russell - If the light is bright enough it actually doesnít matter too much which wavelength it is.  When we say these receptors are most sensitive to blue light thatís the wavelength if you were to lower the light levels it would then be blue that is effective.  If youíre using a full spectrum lamp thatís bright enough it will be perfectly good.

Chris - So this is where people would perch themselves in front of a bright lamp in the morning?

Russell - Thatís right, yes.

Chris - And this works, does it?

Russell - Remarkably enough it works.  Now weíre beginning to understand the mechanisms behind it.


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Colin Donnelly asked the Naked Scientists: I was listening to your show from the 3rd Feb when you mentioned your IR camera and light bulbs. This set me wondering about my new anti-S.A.D. (seasonal affective disorder) 'Full Spectrum' bulb. I believe it emits (more or less) the same visible spectrum as the Sun. However, it is still an energy saving bulb, so presumably it isn't emitting much else (i.e. heat). I also believe that S.A.D is caused by lack of sunlight... hence the bulb. What I don't understand is how the whole thing works. Is it all to do with the production of vitamin D, or is there more to it? Ta much Colin Donnelly What do you think? Colin Donnelly, Fri, 4th Jul 2008

Hi Colin

When you use the light do you alter your posture at all, I.E sit up stand up or do you remain laying flat in bed the whole time and does it have any affect on you personally.

Very interested in this subject.

Thanks Andrew Andrew K Fletcher, Fri, 4th Jul 2008

Hi Andrew

I use the bulb where I work (at a computer), so I'm sitting beneath it most of the day.
I used it for most of last winter and I think it helped, but moods are a very difficult thing to assess.

Colin Colin Donnelly, Sun, 6th Jul 2008

The programme I saw on it's use required the user to be exposed to the light during the night and always sitting or standing rather than laying down. It occurred to me during the programme that it might not be the light that is assisting the people with this condition. Could it be that the longer dark hours during the winter result in longer periods of sleep, and could it be that sleeping less In the summer as the sun rises earlier may be as important as the sunlight?

Recent research into posture and gravity has been revealing some pretty convincing changes in a range of medical conditions that are not fully understood and believed to be irreversible. The object is to tilt a bed so that the head end is higher than the foot end by 15cmís.

Sunlight also changes the humidity of the air by drying everything out faster. So could humidity also be playing a part in SAD?

Andrew Andrew K Fletcher, Mon, 7th Jul 2008

No; the research on this is very clear. The light directly influences the hypothalamus via a secondary branch of the optic nerve, which supplies the suprachiasmatic nucleus (the master body clock). These nerve fibres have their origin in a group of specialised retinal ganglion cells that use a specialised photopigment that bleaches (reacts to light) at 480 nm (blue); their main role (as far as we know) is body clock entrainment / resetting.

Thus, reduced drive to the clock seems to cause circadian rhythms / other physiological systems governed by the hypothalamus, including mood and arousal, to become suboptimal. Light exposure, using a lightbox, seems to improve the situation.

Chris chris, Tue, 8th Jul 2008

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