Perennial Moonlight, Ctd

Jul 11 2011 @ 8:37pm


by Zoë Pollock

Hal Espen railed against the sodium-vapor lighting that radiates from most streetlamps. A reader corrects his insinuations about the filter used in films to recreate it:

The color filters ('gels') that are categorized as "bastard amber" — and there are several variations of greater or lesser color saturation — are not called that because the color is offensive or unpleasant. Bastard ambers are actually some of the most flattering for human skintones (Caucasian, Asian, or African). They are referred to as "bastard" colors because the amber has been bastardized by the influence of other tones… mostly, pink. They therefore do not reside purely within the amber section of the color spectrum. Don't let Hal Espen's mis-implication of "bastard" in this context (with the unspoken presumption of illegitimacy or undesirability) mislead you. Don't read "bastard" amber as undesirable or unflattering… read it simply as "hybrid."

Another reader pointed to this 1991 LA Times article that had astronomers begging for low-pressure sodium lights. Another echoes the point:

The International Dark Sky association has been fighting for years for cities to adopt saner nighttime lighting policies in the name of conservation and letting people actually see the night sky (I teach a large introductory astronomy class;  most of my students have never seen the Milky Way, the most obvious and beautiful night wonder).  Cities waste huge amounts of light (and therefore energy) with lights that shine up as much as down, and keeping deserted areas brightly lit on the off chance that someone will pass through.  Homeowners flood their empty backyards with light under the mistaken impression that it deters burglars. 

Astronomers are particularly aware of this light, as it directly interferes with their telescopes' ability to detect faint objects.  The astronomer's favorite streetlamp is the low pressure sodium lamp, wich produces an orange light that spans an extremely narrow color range.  Special filters can mask this light out as it scatters from the atmosphere, allowing their instruments to see the sky as though the lamps were not there.  Car dealerships hate them because you can't distinguish colors under them — everything is in black and orange — but cities (should) love them because they are relatively efficient.

There is potential for LEDs, which intrinsically produce a single, pure color, to provide similarly filterable light, and do it in a "smart" way that minimizes the amount of light produced overall (through dimming and motion sensitivity) but still provides a sense of the color of the objects they illuminate.  But there is also the danger that in the rush to get all new lamps, cities will opt for LEDs with white phosphors and fancy-looking fixtures without top screens, and the problem of light pollution will go from merely very bad to all but intractable.

(Image: Light Painter by Tang Yau Hoong)