Recently, while watching my Mac reboot, I was idly wondering why it is that blue is such an attractive color on LCD screens. My phone, my home Windows machines, and my work Apple machine all come with blue as the default background color. I thought perhaps there was something special about blue in either or both CRT's or LCDs, hence the importance of the Blue Screen of Death, and not a reflection of aesthetic dominance. But perhaps we have an innate preference that broad, bright swathes of light to be blue? Via MemeMachineGo, I came across this timely graph of hours of daylight as a function of time of year, calculated for Philadelphia, by Leslie Ellis. Ms. Ellis's point was that around the Autumn Equinox ( i.e. the last couple of weeks), from day to day we lose daylight faster than at any time of the year---which might make this the point of most obvious decline for sufferers of Seasonal Affective Disorder, a category of depression that is exacerbated by lack of sunlight and significantly relieved by timed, direct exposure to bright light.

It has been a gorgeous few days in the Bay Area recently, and I've been struck at how much pleasure I get just from looking at the blue sky. Apparently this is not mere poetic fancy. In spring of 2005 Science News Online noted that light therapy for depression is accumulating more and more clinical evidence of potency, and this last spring it noted that blue light may be particularly crucial to human moods: Researchers at Thomas Jefferson University in Philadelphia launched a five year study to find out which hues of light are the most effective in treating sleep and mood disorders, and were surprised when their research indicated blue hues win out. They were surprised because our rods and cones--the cells in our eyes with which we collect color information for image transmission to our brains--are not very sensitive to blue. But a separate researchers at Brown University have recently discovered a new, very small class of eye cells that do not help us "see" better, but which do detect blue light better. These cells were discovered because of blind rats who still have light-sensitive circadian rhythms.

To Figueiro, the ganglion-cell discovery confirmed that "our eyes are effectively blue-sky detectors."