This doesn't seem immediately obvious to me. Care to explain? Incandescent lightbulbs are a time-proven technology with economies of scale behind them. They generate heat and light, which is what's required here. Seems ideal for the application.
Really? Even assuming that we absolutely need to heat up the lights to solve this problem, we only need to do it when there is enough snow on the light to be a problem, which means at most only during snowfall, realistically much less frequently than that. Even in New England during winter, you've gotta be talking under 10% of the time that this has to happen.
You seriously can't come up with a better way to solve this problem than replacing a very efficient, very robust light source with a very inefficient, very delicate one, secure in the knowledge that as it runs all year round, some tiny fraction of the huge amount of waste heat it generates will go towards melting snow?
Although I'll note in your defense that "incandescent lightbulbs" are more accurately described as "heat lamps", and one potential solution might well involve a specialized heat lamp which only activates when the light itself is obstructed.
A traffic light is already half of a snow sensor by virtue of being a light. If it's covered with snow, the snow will reflect light back. Add a few photoresistors and you're in business. It'd be the cheapest part of the whole project.
You can use a regular resistive heating coil. You can design a heating coil that will never burn out. LEDs themselves can last over 10 years. Thus the combination of led plus heating coil will last you more than ten years. Incadescents on the other hand burn out all the time especially when they need to be turned on and off very often, as in traffic lights. For an American city the upkeep of traffic lights is more expensive than the hardware. Also traffic lights that burn out will cause dangerous co fictions and may cause accidents.
How do cars defrost the rear windshield? Embedded heating elements in the glass. That's pretty proven, and easy to manufacture. The exact same thing could be used here.
That works for frost, but I still need to clear the windshield after it snows. I dunno how hot those defrosters will go if you really crank 'em, though...
Apropos of nothing, but this just made me look up "defroster" on Wikipedia... "For primary defogging, heat is generally provided by the vehicle's engine coolant via the heater core; fresh air is blown through the heater core and then ducted to and distributed over the interior surface of the windshield by a blower. This air is in many cases first dehumidified by passing it through the vehicle's operating air conditioning evaporator." Wikipedia makes everything so cool.
