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When I drive at night, I always notice something odd about stoplights. I pull up to a "stale red" light (that's when it's been red for a while), and wait. Then when the light turns green, it looks and feels brighter, almost a little bit startling. The mild startle effect is actually helpful when I feel tired, because it prompts me to react and start moving. I don't notice the difference if I go through on a "stale green", but when it just changes, the difference in brightness is quite noticeable. And I haven't paid attention to how the difference feels during the change from green to yellow to red, because I look at the road, rather than the stoplight.
The difference is most noticeable on newer stoplights that still use incandescent or maybe halogen light bulbs. That's where the change from red to green feels almost jarring. (Which isn't a bad thing.) But it's also noticeable, albeit less so, on very old incandescent stoplights, which are quite dim overall, and on recently installed LED stoplights, which vary in brightness.
I once read that short-wave lights (blue and blue-green) have a rousing effect, because they suppress melatonin. This is not true for long-wave lights (red and orange). I also read that the green light is sometimes made slightly bluish, to make it visible to red-green colorblind people (the most common type, and they can see blue). The red light, in turn, is made very slightly purplish, to keep it from looking like it's off.
Is my observation correct? Is there any actual difference in brightness between red and green lights, or is it just my mind reacting to the difference in color?
Last edited by MillennialUrbanist; 07-23-2018 at 01:59 PM..
The eyes are most sensitive to green and least sensitive to red and violet in the visible light spectrum. They probably manufacture them all to a similar wattage without taking this fact into account. It's most likely a evolutionary adaptation to the fact that we basically evolved in a green environment. Anyone who's ever used red and green laser pointers when they hit peak popularity around 10 years ago is aware of this as well.
More interesting reading on using red and dim green light to maintain night vision:
Don't know if there is a difference but to get our attention, my local DOT people experimented with a small white strobe light that was installed in the red light. It flashed while the light was red. It was removed after 30 days.
Don't know if there is a difference but to get our attention, my local DOT people experimented with a small white strobe light that was installed in the red light. It flashed while the light was red. It was removed after 30 days.
They screwed the pooch by putting a strobe light into the red light. The strobe light didn't provide much benefit to the colorblind; it just annoyed everyone waiting at the red light, unable to escape the flash.
It makes a lot more sense to have the strobe light in the green light. Then, it can jar a drowsy driver awake when the light turns green, and they'll just drive away and not have to look at the flash. Although even then, a strobe light can be seizure triggers for drivers with epilepsy. And if someone has a seizure while driving, they can get injured and/or cause an accident. So it's better to make the lights in a slightly different brightness, like I thought they were in the original post. Or add a visible symbol to each light; Japan does it.
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