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Hello All list members ;
I am the Director of Engineering at Ecolux
International in Thailand. Just found and signed up to your good list
while surfing. Native NY'er.
There are some list questions about dimming of LED
traffic signals. Most LED traffic signals use a switching power
supply (for line isolation and high energy efficiency) to convert
220V/120VAC to 12V or similar low voltage to drive the LED's. This power
supply does not respond well to phase cut dimming. That's why most (but
not all) LED signals are not dimmable using ordinary phase cut dimming.
Then normally 3 or 4 LED's are wired in series with one current limiting
resistor (depending on the voltage drop of the LED's. Voltage for green is much
higher than red). Super bright LED's last a long time if the circuit is
properly designed (MTBF > 2,000,000 hours at room temperature), and this
power supply normally is the limiting factor for the MTBF (Mean Time Before
Failure) of the traffic signal.
We manufacture a line of traffic signals that are
dimmable using ordinary phase cut dimmers. These signals do not use a
power supply. They respond well to phase cut dimming. The only problem you might experience is that most triacs in
even a small dimmer control are rated 600 watts or more. Now in simple
terms, the triac is normally pulsed to switch it to the "on"
condition. Then it is held conducting (on) by load current.
Since an LED traffic light only uses 4-5 watts, the low load current
may not keep the triac on reliably. This results in severe and
unacceptable flicker at dimmed settings. One solution (don't laugh) is to
use another load (like a big power resistor), to hold the triac on. Of
course this eliminates the benefit of power savings for the LED signal, so
clearly not recommended. The recommended method is to use a dimmer
rated for very small loads.
We also do automatic night time dimming by
photocell sensor and dimming solar flashers. Most of our sales
are 220V, but we are starting to get 120V orders. Our signals lack
regulatory approval, which you may need (Thailand has no regulatory requirements
yet). So just thought you might like to know that dimming is very
possible. Lots of info, reliability info, and specs on our web site.
I hope this post is not too commercial. Moderator feel free to
cut.
Best Regards,
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