At 02:01 PM 3/23/2009, David Beierl wrote...
>What's the ratio difference in light output between them and the
>stoplights?  If I'm reading FMVSS 108 correctly, the currently allowed
>range for tail light lamps is 2-18 candlepower, and at 15 cp the #93
>bulb meets this.  But the currently allowed range for stop light lamps
>is *80-300* cp, a minimum ratio of 4:1 and maximum of 105:1. At 32 cp
>our 1156 stop lamps would only give a ratio of 2:1.

1) Current FMVSS don't apply to our older vehicles, which are
grandfathered. I don't see any reference in 108 (
http://edocket.access.gpo.gov/cfr_2004/octqtr/49cfr571.108.htm ) to
"candlepower," "cp," or "ratio." Perhaps you can provide a more
specific citation?

2) 80 cp sounds way to high as a minimum for a stop bulb. The 1156 is a
common US stop light bulb, and puts out 32 CP.

>I'm looking for SAE standards J585d and J586c which I *believe*
>covered the candlepower requirements for our lights when they were
>made, but only finding references to them so far.  But a #89 bulb is
>rated 6 cp, which would give a 5:1 ratio stop:tail, so I think the
>spirit of the regs is plain -- they continue to want at least a 4:1
>ratio.

The spirit of the regs is indeed plain, that the stop lamps should be
clearly noticeable in the presence of tail lamps. The separate stop
lamps, and the difference in color (orange vs. red) which most European
vehicles, including the Vanagon, have, makes that easier to achieve
without having as much of a brightness difference necessary for
combined tail/stop lights, as many US cars have.

When SAE standards are freely available, I might consider accepting
them as a legitimate part of unconstitutional regulatory "law." If they
reference candlepower, they're fatally flawed. CP is a good indication
of light output for different bulbs used in the same fixture, but
worthless for comparing relative brightness of bulbs in different
fixtures (such as on most Euro cars, including the Vanagon). For that
you need to look at lumens.
'