Daniel J. Stern wrote:

On Mon, 21 Feb 2005, Douglas G. Cummins wrote:


When LED traffic signals were in their infancy the specs were all
written around incandescents and so didn't address characteristics
particular to LEDs such as intensity and color drift over time. The
Institute of Traffic Engineers (ITE) just released a Draft of a proposed
spec (although it may now be final) for LED Traffic Signal Heads for US
roads. I don't know what's in effect for Europe, etc.


Europe doesn't have the glaring-green problem we've got in North America,
'cause their LED traffic signals have variable intensity that dims and
brightens with ambient light conditions. I'll be very surprised if any
glare-control measures at all made it into the ITE spec; glare is
generally ignored (dismissed as a non-problem) in North America.

New spec has maximum permissible luminous intensity not to exceed three
times the minimum required peak intensity. Also allows the option of
nighttime dimming so long as it does not drop below 30% the minimum
maintained luminous intensity (in other words, can be variably dimmed
dependent on ambient light). Also, luminance across the entire lens
must be uniform, not exceeding a max to min ratio of 10 to 1.

So glare is not ignored - it just wasn't considered previously because
when it was just incandescent traffic signals no one was going to make
their lamps too bright due to heat and energy cost issues. It just
takes longer for the specs to catch up. Now that there's a
specification in place, it's up to the municipalities to make sure their
existing stock and/or new stock meet the published requirements.

--
Douglas Cummins
Calcoast - ITL