On 12/4/2012 5:47 AM, Henry Baker wrote:
(Full disclosure: my father worked for Ford Motor Co., Edsel Division(!), in the 1950's.)
The "Federal Motor Vehicle Safety Standard 108" is online (referenced from Wikipedia), and is a perfect example of too much detail embedding obsolete technology into law. For example, headlights are restricted to 55-70 watts at 12.8 volts. Elsewhere, the brightness is limited in candela. There is a very detailed specification of the abrasion resistance of the headlamp cover, including the size of the abrading grains, or the coarseness of the steel wool.
In the 1940's, Edwin Land, the inventor of the Polaroid instant photography, tried unsuccessfully to polarize headlights and windshields in orthogonal axes; he finally gave up in 1947. I estimate that his invention could likely have saved ~10^6 lives during the past 70 years.
Billings, B.H. and Land, E.H. "A comparative survey of some possible systems of polarized headlights". J. Optical Soc. of America, 38(10), 819-829, Oct. 1948.
The 1948 Tucker had steerable headlights. Steerable headlights were subsequently banned, and precluded the importation of the innovative Citroen SM into the US until its steerable headlights (& many other features) could be disabled.
Very hi-tech and complicated - but innovative? No other manufacturer adopted steerable headlights (which were used earlier by Tatra) or air-over-oil suspension, and even Citroen didn't continue with those technologies.
The US auto lighting regulations also discouraged "non sealed beam" headlights, which completely stalled vehicle lighting innovation for 30-40 years.
I don't think so. The standard was adopted to get rid of the bulb and unsealed reflector lights which were common before WW2. Their problem was that the reflector would get dirty from condensation and even corrode. Motorcycle headlights were never required to be sealed beams (because it's easy to carry a spare bulb, but not a whole headlight) but there was no great innovation or superiority in motorcycle lights. Brent
These obsolete regulations were used (successfully) by the U.S. auto manufacturers to keep out foreign cars and protect domestic manufacturers. ---
Here are the specifications for the vehicle light colors, referencing the CIE color chart:
Red. Red is not acceptable if it is less saturated (paler), yellower, or bluer than the limit standards.
Yellow (Amber). Yellow is not acceptable if it is less saturated (paler), greener, or redder than the limit standards.
White. White is not acceptable if its color differs "materially" from that of CIE Source A.
Red. The color of light emitted must fall within the following boundaries:
y = 0.33 (yellow boundary) y = 0.98 - x (purple boundary)
Yellow (Amber). The color of light emitted must fall within the following boundaries:
y = 0.39 (red boundary) y = 0.79 - 0.67 x (white boundary) y = x - 0.12 (green boundary)
White (achromatic). The color of light emitted must fall within the following boundaries:
x = 0.31 (blue boundary) y = 0.44 (green boundary) x = 0.50 (yellow boundary) y = 0.15 + 0.64x (green boundary) y = 0.38 (red boundary) y = 0.05 + 0.75x (purple boundary) --- There must be a chart showing these regions on the CIE diagram, but I couldn't easily find such a chart.
There is a way to convert these specifications into wavelengths, but it's a bit complicated, because the specifications are specified with tristimulus coordinates.
At 11:21 PM 12/3/2012, Bill Gosper wrote:
[Not math, but hopefully fun] Automotive lights: Besides the traditional yellowish white headlights, we're seeing cold white, and pale green, blue, pink, and lavender. Plus those annoying prismatic things. But crawling down I280 tonight, I was struck by the uniformity of the red in the miles of taillights stretching out before me. Both LED and conventional. Is there some strict spectral standard? Or does my color discrimination roll off fast at the red end?
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