Chapter

Light and non-visual photoreception

Dan A. Oren and Paul H. Desan

in Seasonal Affective Disorder

Second edition

Published on behalf of Oxford University Press

Published in print October 2009 | ISBN: 9780199544288
Published online February 2013 | e-ISBN: 9780191754593 | DOI: http://dx.doi.org/10.1093/med/9780199544288.003.0008
Light and non-visual photoreception

Show Summary Details

Preview

The evidence to date supports the view that short and/or middle wavelength light is therapeutic in SAD. The observation that treatment consisting of short wavelength light or concentrated in short wavelength light is at least as effective as broad band white light is consistent with the hypothesis that short or middle wavelength light is more effective per unit of lux, but does not prove this hypothesis. The definitive experiment showing that blue or green light is more effective than longer or shorter wavelength of greater lux, of greater perceived brightness, simply has not been done. It is tempting but premature to speculate that the therapeutic effect of light in SAD is related to a putative melanopsin system.

Understanding the mechanism of light's therapeutic effect in SAD is important not only theoretically but practically. Knowing the most effective wavelength distribution may enable more efficient and more effective treatment devices. Even if a particular wavelength is found most therapeutically potent, it may not be the optimal clinical approach, for example blue light is more phototoxic to the retina, and light of a bit longer wavelength could prove safer. One could even hypothesize that a particular pattern of changing wavelength may be the most potent therapeutic approach. The research agenda suggested by the first law of photochemistry called simply for matching the action spectrum of the physiological response to the action spectrum of a pigment. This agenda still applies, but may entail a more detailed model with multiple photopigments with complex interactions behind a lens with wavelength-dependent absorption. Once again nature hides her secrets well.

Chapter.  5512 words.  Illustrated.

Subjects: Psychiatry

Full text: subscription required

How to subscribe Recommend to my Librarian

Buy this work at Oxford University Press »

Users without a subscription are not able to see the full content. Please, subscribe or login to access all content.