Science Questions

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?

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

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

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 15cm’s.

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

Andrew

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