Green Laser Pointers vs. Red Laser Pointers
by adminMany years ago, laser pointers were a very expensive luxury that only a few folks could afford. Even when they could afford them they were rather hard to find and had lots of other issues like being oversized and eating batteries. But as time went on the production of red laser LEDs dropped dramtically and soon laser pointers were priced at the level where they could be even bought just for teasing and playing with the cat.
About the time that red laser pointers became very affordable, the first green laser pointers appeared on the market. Like the first (red) laser pointers these were very expensive. The average price for a bulky green pointer was about $500. But like many other things in the electronics market the price started to drop as production costs fell. These days it it not unreasonable to find a green laser pointer for less than $100.
But why would one want a green laser pointer when red ones can be had for under $10? The answer is simple: The human eye is much more sensitive to green light, especially under daylight conditions, where our eyes are as much as 10 times as sensitive to green light as they are to red. If one is using a red laser pointer in a brightly lit lecture hall, it might well be hard to see by people attending the lecture. But use a green laser pointer and even folks sitting in the back will be able to see where you are pointing. Yet both the green laser and red laser will be putting out the same amount of power.
We made a short video to demonstrate this effect:
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The differences between red and green
The price of green laser pointer is much higher than red laser.
Here’s sth I don’t quite understand: Red light travels fastest of the 7 visible wavelengths agreed?
Then why do green lasers (green light) catch the human eye better than red? Were the voltages used in the lasers the same?
If green catches the eye better, then why do all military reflex sights use red-dots and not green?
John,
Red light travels no faster or slower than green (or blue) light. Its all going the speed of light. Yes, I know in a medium red’s long wavelength will allow it to go slightly faster, but nowhere near enough to matter for human impression.
The Green light catches the human eye has nothing to do with physics. It has everything to do with the human eye’s construction. The human eye is much more sensitive to wavelengths in the middle of the visible spectrum (yellow, green) than near the ends (red, blue-violet). This is a biology cause, not a physics cause.
As for why military reflex sights use red dots, I can think of three reason:
1) Red light does not interfere with night-vision. The same reason astronomers use red colored flashlights when observing. A green flashlight would spoil night vision.
2) Green dots are bright enough to actually reflect off the human eye or even the face! You probably wouldn’t want to run around the battlefield at night with your face lit up. It would make you a bit of a target.
3) Until recently, Green LEDs and lasers were much more expensive than red ones. Even now they are much more expensive, just not quite as much as from 5-10 years ago.
Hope this helps!
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