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This is mostly for my own personal illumination, and isn't directly related to any school or work projects. I just picked up a trio of laser pointers (red, green, and blue), and I notice that when I project them, the red and the blue appear to be dimmer to my eye than the green one. I had a fleeting suspicion that, perhaps this is an effect of blue and red being at the periphery of the visual light scale, but I honestly have no idea if this is the case or if it's just my eyes playing tricks on me. All three lasers have the same nominal strength, in this case.

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3 Answers 3

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Human color vision is based on four types of receptors in the retina: rods, and three types of cones. Their response to different wavelengths is shown in this graph:

enter image description here.

It shows clearly how certain wavelenghts, mostly around the yellow-green portion of the spectrum, are absorbed more strongly, and by more types of cells, than the rest.

So it is normal that, even with equal powers, some colors are seen brighter than others. Actually, digital cameras often filter their CCD array with a Bayer mask, which has twice as many pixels filtered green, as red or blue, to better simulate the eye's color sensitivity.

enter image description here

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Three cones for most people. There are a few of us who have only two and even fewer who have four. And I believe it is because our rods are most sensitive to green light (and hardly at all to red light) that we are most sensitive to the color green. –  Octopus 2 days ago

Its because human eyes are more sensitive to green light than other colors. Here's a reference:

I also heard from a friend, although I can't find a reference, that traffic lights display red at a higher intensity so that it appears just as "bright" as green light does.

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Found something helpful: Apparently, we see green light approximately 50 times brighter than red –  QEntanglement Oct 24 '12 at 23:55

A less scientific answer: It may also just happen that the green laser is more powerful than the others.

In fact, humankind always had great problems making a green laser diode, whereas the red and blue ones are readily available. The green pointers contain a full-fledged Nd:YVO4 DPSS laser oscillator with built-in KTP frequency doubler.

I have measured two green pointers with precise power meter, and both greatly exceeded their nominal values. In fact, their power was illegal to be sold in my country...

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But have you measured a green and red laser to have the same power and then looked at them to see which looked brighter? –  Brandon Enright Sep 30 at 4:18

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