Old 08-07-2007, 11:23 PM #1
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Default How many times is Green brighter than Red?

I forgot the exact numbers
its like 1mW Green = 8mW Red?
In terms of visibility.
anybody remember?

and for green pointers 4x the power = 2x the visibility of the beam right?

just been bothering me all day cuz I can't remember lol


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Old 08-08-2007, 02:50 AM #2
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Default Re: How many times is Green brighter than Red?

1mw of green is just as bright as 1mw of red... now what the eye sees is diffrent.

so let's say blue has a value of 1w

red will appear as bright as the blue with a value of 600mw

green will appear as bright with a value of 400mw


what is strange is that the eye has the most red cones, almost 70% are sensitive to red, while only 40% are sensitive to green, and only about 2% are sensitive to blue. ( yes the math doesn't = 100% because some are multicolor sensitive. ) this doesn't even count the rods which are your night vision and are slightly color responsive but mostly it's on or off for them.

What's interesting is that the blue cones are the most sensitive. a slight amount of blue triggers them and they are about 15% of your vision while only being about 2% of your retina. it's why blue leds are so damn annoying at night. Red is the most vision friendly, it's why you can look at red flares without much afterimage and red lighting doesn't bother your night vision, but if you do get a blast of green it is the most likely to disrupt your vision. it's the next most sensitive, almost 60% of what you see is green. the rest is left for red, about 25%

keep in mind the eye sees color strangely. yellow can be made out of many combinations of red and green, and all will appear the same shade as yellow. All the colors together make white.

now for lasers, it's basically about 4 times the power to double the apparent brightness. it's actually something like 3.7XX 4 is good enough for me, same with most of the crap above, I just ballparked it all to make it easier to digest.
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Old 08-08-2007, 04:23 AM #3
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Default Re: How many times is Green brighter than Red?

I have heard amounts between 6-8x brighter... But I don't really know myself. I do know it varies per person... Little OT, but speaking of rods and cones, One of many quirks about me is that my right eye never shows red colors properly. They almost always appear as brown or orange-- Not with a laser, mind you, its just way dimmer than normal... But it makes it hard to use binoculars because I only end up looking through my left eye, then get a headache! ;D

But yeah, my eye doctor said thats perfectly normal-- In fact, he said most people have the same thing happen with any given color, but so slightly they don't realize it. I am like, off the charts... :P

Another cool quirk-- I can spray liquids out of my eye by inhaling them through my nose... This also means when I eat a ton of chocolate, cause of an allergy, I get a nosebleed... And then I can squirt blood out of my eyes!! 8-) 8-) 8-) 1 in 20 people have a malformed tear duct that enables them to do that... Might want to try it yourself! Your dentist should also be able to tell you if you have one, as long as they have old X-rays...
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Old 08-08-2007, 04:30 AM #4
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Default Re: How many times is Green brighter than Red?

im prettty sure it was 8x
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Old 08-08-2007, 01:32 PM #5
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Default Re: How many times is Green brighter than Red?

Depends on the frequency of the red. Near 635nm the sensitivity of the eye is rapidly increasing.

This graph shows peak color sensitivity in the green, rapidly fading off either end (blue, red). This is why green appears so much brighter.. just a bias of our eyes.



You can also see Sam's FAQ for some numbers:
http://www.repairfaq.org/sam/laserioi.htm#ioicav2

532 nm is about 88% of peak (which is ~555 nm)
635 nm is 22%
655 nm is 8%
660 nm is 6%

So, roughly, you need about 4x as much 635nm to match 532nm, and about 10x (or more) for the more common 655-660nm. There's a tendency for high power diodes to shift to longer wavelengths, so I'm guessing most DVD burner diodes are closer to 660nm than 650nm.

Anyway, these numbers are approximate. Each person is a little different.

Edit -- Zeno, my eyes color balance (whatever) is slightly different. But it's subtle and I can only notice in good light if I compare the view between the two.
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Old 08-08-2007, 02:34 PM #6
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Default Re: How many times is Green brighter than Red?

ah thx flogged
that helped a lot
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Old 08-08-2007, 07:10 PM #7
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Default Re: How many times is Green brighter than Red?

Yeah, it really depends a lot on the wavelength of the red. In laser projectors you sometimes see a 635nm red component that's even weaker than the green, whereas when you use 671nm, you need much more red than green. Also, it depends on the conditions. The graph posted above refers to photopic vision - when there is plently of light around. However in scotopic/dark vision, the peak is actually in the blue range - not green.

Also, you have to take things like beam diameter into account if you're comparing lasers. A 130mW 660nm pulsar looks almost as bright as a 4mW 532nm leadlight at night. That's a >30x difference, but the pulsar also has a larger beam diameter.

Overall, its just my opinion that there are too many variables involved with perception to state definite numbers and formulas, but if you're looking to compare colors mathematically, the 1988 CIE photopic luminousity function is your friend: http://members.misty.com/don/photopic.html
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