So, people see best in the wavelength around 500nm which is a green/blue color. Why aren’t car headlights this color to improve visibility? Why can’t you buy headlight bulbs that emit bright green light? A white light with a green filter would just make it more dim, but on headlights you want brightness.
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> So, people see best in the wavelength around 500nm which is a green/blue color
This is an extreme misunderstanding of the fact that humans are better at discerning between shades of green than of other colors. A human would be able to see someone wearing all green against a slightly different green background, or at least see them better than someone wearing all red against a slightly different red background. But, that’s only true if they are being illuminated with white light. If they were being illuminated with pure green light, the green person against the green background would be nearly impossible to see, and the red person against the red background would be literally impossible to see. By using fewer wavelengths of light, our eyes would have less information and would differentiate between things worse.
> people see best in the wavelength around 500nm which is a green/blue color.
Our eyes are most sensitive to that wavelength but our colour vision obviously needs others. Saying we see “best” is not accurate, because vision is more than just brightness. There have been studies on the safety of things like street lights, and those yellow, sodium-based bulbs are worse, even at the same brightness, just because they shine in only one colour.
If headlights are limited to one color, they will severely hinder visibility.
On headlights, you do *not* want brightness. You want the appropriate amount of brightness.
The ideal headlight is bright enough to allow you to see bit dim and low enough to allow other drivers to see. It is also red-tinted to minimize its impairment to night vision.
Green lights are basically going to cause you to see in black and white, and also ruin your night vision. Two things which are very limiting.
This is maybe too simple of an answer, but white light includes green light. White light includes all colors of the spectrum. Also have you actually tried to light your room with only one color bulb? Things always look darker.
Because anything that doesn’t reflect green light would appear black. The brown deer. The pedestrian with the red jacket. The gray K-rail.
People want to be able to see all kinds of objects, even those that don’t reflect green light very well. White headlights do that best; if you need more light then just make them brighter.
Another big issue is that we use traffic signals, and green tells people to go. If headlights were green, especially if it was a somewhat rare option, it would be very dangerous as oncoming traffic could be confused as a signal during a red light.
Because of your last sentence…a white light with a green filter means it’s either not as bright or you need to have a significantly brighter white light to get the brightness of green you want after the filter. And taking out the other colours doesn’t help improve visibility, it makes it worse. The highly visible green wavelengths are still there in the white light, they just have other stuff too.
You could do it with green LEDs but now it’s nearly monochrome and that has major issues with color recognition and it will cause objects that don’t reflect green well at all (things at the green end) dark/black.
Thank you all for your answers. It totally makes sense that non-green objects would appear ‘unilluminated,’ if that’s a word.
I think my idea originated from night-vision goggles being green due to the…. phosphorous? Maybe? It’s been a while.
Maybe I need more experience in different narrow-wavelength lighted rooms.
Again, thank you all for your quick and perfect answers.
I don’t know exactly where the 500nm comes from, but I assume it means that our eyes are most receptive to light with about 500nm wavelengths. However, it is wrong to assume that all light is only a single wavelength. Most light, in fact, is a combination of several wavelengths.
For example, a halogen light (a common choice for headlights) produces every wavelength of light at varying intensities. 500nm is included, but more light simply means more activation.
If you wanted to have a green light, you would need to find a convenient way to produce green light, probably using an LED. However, a green LED headlight is a bad choice – Mostly, a colorblind person might be less receptive to a purely green light as opposed to a full-spectrum light like a halogen light.
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