Why is there a clear light in the traffic signal?

Photo of a traffic signal with a clear lens

Merissa’s photo of her traffic signal

I love it when people contact me with questions about traffic lights after stumbling into my website. I love it even more when I can answer their questions, and Merissa’s was a gem.

Like any red-blooded, level-headed American, she bought a traffic light. Odd thing about it was that one of the sections had, what appeared to be, a clear light, and she wanted to know why. The person she bought it from thought that it may be from a railroad.

Sorry, my dear Watson, but that “clear” light will actually light up green. Many of the LED manufacturers offer tinted and clear options. Generally, the only light that will always be tinted is the red, although I have seen a signal with an clear red.

A few years ago, traffic lights began being assembled with LED inserts rather than a single light bulb in front of a reflector and behind a glass or plastic lens. These newer inserts contain an array of small, colored LEDs, so if some of them fail, you still have a lit indication, rather than a light bulb which can be a single point of failure. LEDs also use less electricity and can be brighter. Some place a clear or diffused cover in front of the LEDs and still have it light up the color of the LEDs, like Merissa’s.

photo of "sun phantom" effect on a traffic light

“Sun Phantom” effect of a traffic light. None of the lights are actually on.

As for the clear-looking inserts go, these have colored LEDs that only show their true colors when lit. This implementation is designed to eliminate “sun phantoming”, a situation where the sun can hit the signal and make it appear that all lights are lit. The non-tinted sections don’t have a color to reflect, thereby showing no indication when sunlight hits it directly.

Seeing all indications lit increases chances for an accident at an intersection due to a confused driver. If you do find yourself in a situation where you can’t tell what indication is actually lit, whether they all look lit or they all look dark, treat the intersection like it’s a 4-way stop.

That explains her “clear” lens. I also pointed out that the bottom section likely contains a bi-modal arrow, a nice little bonus that’s pretty cool itself. But I’ll save that for another post.

Enjoy your traffic light, Merissa! I’d love to see it hanging in your house!

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