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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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What power (wattage) do each of the lasers have? –  Niel de Beaudrap Oct 24 '12 at 22:03
    
They are each labeled to be max wattage of <5mW, I don't think there's other technical details available. I'll see if I can find them. Here are the wavelengths, in case they are useful: 650nm (+/-10), red; 532nm (+/-10), green; 405nm (+/-10), blue. –  TARehman Oct 24 '12 at 22:23
    
As you can see in QEntanglement's answer this is not---strictly---a physics questions. It is, however, frequently asked in various forms. –  dmckee Oct 25 '12 at 0:06
    
@dmckee Didn't mean to be off-topic; I couldn't think of a better SE site for this than Physics. Both the answers below were great. –  TARehman Oct 25 '12 at 2:01
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Well, it's the kind of not-a-physics question that always gets asked on these kinds of sites because until you know the answer it looks like a physics question. I do not intend to close it, because if I did it would simple re-appear later on. –  dmckee Oct 25 '12 at 2:09
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2 Answers

up vote 8 down vote accepted

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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Its because human eyes are more sensitive to green light than other colors. Here's a reference: http://www.physicsclassroom.com/class/light/u12l2b.cfm

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: ehow.com/info_8059871_astronomical-laser-pointers.html Apparently, we see green light approximately 50 times brighter than red –  QEntanglement Oct 24 '12 at 23:55
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