GBlist: Re: SAD Light Treatments and light color

[JamesAWise@aol.com]

GB Listers,

Since it came up in a previous post, I'd like to correct a significant 
misconception about SAD (Seasonal Affective Disorder) light treatments that 
is often found in the popular literature on the subject.

Full spectrum lamps have absolutely nothing to do with treating SAD or with 
synchronizing human biorhythms. The ameliorative effects of supplementary 
light treatments are totally due to light intensity. The relevant 
physiological responses are controlled by a neural connection from the *rods* 
of the eye (not the foveal cones--which mediate color vision) to the 
hypothalamus of the brain, and the rods of the eye are tuned to maximum 
responsiveness in the blue-green part of the spectrum. Actually, they are 
tuned to the color of semi-tropical leaves, because this part of the visual 
system was originally selected for and operative in forests at night.  The 
diurnal timing in release of neurotransmitters like melatonin is under 
control of a very biologically primitive part of the visual system.

So, if one wants to treat SAD, it's best to use straight old coolwhite 
fluorescents in those light boxes!  Full spectrum fluorescents are 
unnecessary in light therapy for SAD.

I'd also like to note that Human Factors research in lighting over the past 
30 years has greatly reduced purely 'subjective' speculations about 'light 
color' (i.e. the power spectrum of a lamp) and human response.  There is good 
evidence in such studies to validate in detail the shift in preference to 
'warmer' lamp colors under conditions of lower illumination, suggesting that 
'daylight' lamps are not a good choice for residential living areas after 
dark.

As far back as the late 60's, the NBS (now NIST) developed a metric 'flattery 
index' of lighting which describes how well people of different skin tones 
are rendered under different power spectra of illumination. This again shows 
the personal rendering advantages of 'warmer' lighting under lower light 
levels. That research has been widely used in restaurants, where pink lights 
have now become rather common enhancers of the setting.   As previously 
noted, lampshades and/or sepia washes on the interior of glass shades can 
also be used to warm up the color of a 'daylight' bulb. 

The Lighting Handbook of the Illuminating Engineering Society has good 
discussions of these issues.

Sincerely,

Jim W.

James A. Wise, Ph.D.
CEO, Eco•Integrations, Inc.
2620 WillowBrook Ave.
Richland, WA 99352

tel & fax: 509-627-5869
email: JamesAWise@aol.com



______________________________________________________________________
This greenbuilding dialogue is sponsored by CREST <www.crest.org>
BuildingGreen <www.buildinggreen.com> and Oikos <www.oikos.com>
For  instructions send  e-mail to  greenbuilding-request@crest.org.
______________________________________________________________________