Old 09-13-2008, 01:12 PM #1
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Default The eye's sensitivity to brightness *Read*

Okay, I have seen alot of posts around here with people going "I got a new laser, but it looks like the same brightness as my lower power one, whats wrong?"

Well, the answer is this. Putting aside your laser MAY be underpowered, lets just assume they are correct in thier ratings for now.

Our eye's sensitivity to brightness IS NOT linear! Meaning, after you get to a certain power, it takes ALOT more power to achieve a brighter laser!

For example, My scanner originally used a 40mw green. Now I thought this was getting kinda dull, so I went out and bought a 100mw CNI module, doing about 141mw. Its 3 times the power, so 3 times the brightness? WRONG!

Actually, there was only a tiny difference in brightness between the 2 lasers! After the CNI had a warm up, you culd slightly see a difference, but deffinately not what I was expecting. This is due to your eye's brightness sensitivity not being linear!

Some people try pot mod thier lasers, and yes you may get about more power out, but unless you pot mod it to the max, the brightness isnt gonna be as good as you expect, up to a point. Sure, if you pot mod a 5mw, then you will see a difference, but do it to a 100mw, and it will take ALOT of modding to acheive anything brighter.

Think of this as a rule of thumb: To get 2X the brightness, you need about 4X the power!

As I said, this is up to a point. Below 30mw, you should be able to notice the difference, but go too high above that, and it takes ALOT more power. Hope this helped anyone wondering ! *


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Old 09-14-2008, 02:17 PM #2
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Default Re: The eye's sensitivity to brightness *Read*

Hmm...I have known about this, however I can't help but to think about something: If you have two 50mW lasers that you combine , you'll have 100mW.Will it not be twice as bright?

I'm just trying to imagine 2 exact same brightness dots on the wall joining and forming a less than twice bright dot which would look weird. :P
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Old 09-15-2008, 09:27 AM #3
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Default Re: The eye's sensitivity to brightness *Read*

Well, it WILL appear brighter, but it wont be twice as bright. The beam, actually gets brighter.
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Old 09-15-2008, 10:10 AM #4
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Default Re: The eye's sensitivity to brightness *Read*

The eye works somewhat logarithmic actually, and it has an AGC (Automatic Gain control), in the form of an iris, to make things of greatly differing brightness to about the same brightness.
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Old 09-15-2008, 04:34 PM #5
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Default Re: The eye's sensitivity to brightness *Read*

It's' kinda similar to horsepower in a car. You will detect a huge power difference from 100hp to 200hp, but not so much between, lets say, 600hp and 700hp. The difference between 100hp and 200hp is approx 2.5 sec. in the 1/4 mile for the 100-200hp, and approx 0.5 sec for the 600-700hp. Now I know allot of other physics exist in this scenario that don't apply with light, but the concept is somewhat similar. I don't believe it is even our eyes that fail to detect the amplification difference, but simply physics. 5mw green vs 10 mw green looks like 10mW (green looks more powerful then it is) vs 11mW (slight noticable difference) and 100mW vs 200 mW LOOKS like 100mW vs "what should be”(to our eye) 125mW.
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Old 09-16-2008, 05:32 PM #6
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Default Re: The eye's sensitivity to brightness *Read*

I noticed something very strange.
I've finished my 166mW violet, and the spot looks like it's around 10 times brighter than my 54mW. My first thought was, Li-ions in the 54mW must be empty, so I aimed it at the meter and it still produced 48mW. That's a brightness difference of 3.46, not nearly the difference it looks like.

[edit] Only when looking through safety goggles it does look like a correct difference.
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Old 09-16-2008, 07:17 PM #7
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Default Re: The eye's sensitivity to brightness *Read*

You probably got a slight difference in wavelengths, so the stronger one does look even stronger...

You posted at 5:32. Donīt know why, but I had to smile...

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Old 09-16-2008, 07:19 PM #8
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Default Re: The eye's sensitivity to brightness *Read*

Quote:
Originally Posted by Zom-B
I noticed something very strange.
I've finished my 166mW violet, and the spot looks like it's around 10 times brighter than my 54mW. My first thought was, Li-ions in the 54mW must be empty, so I aimed it at the meter and it still produced 48mW. That's a brightness difference of 3.46, not nearly the difference it looks like.

[edit] Only when looking through safety goggles it does look like a correct difference.

Differences in wavelength will do that. Several people are beginning to look at the phenomenon of brighter "405nm" beams. The idea at the present time is that you are seeing normal range of wavelengths but one is at the bottom (400nm) and the other is at the top (410nm). The closer to UV, the harder the beam and spot are to "see."

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Old 10-24-2008, 11:34 AM #9
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Default Re: The eye's sensitivity to brightness *Read*

you should make a graph, interesting... 8-) and ofcourse useful.
but, my ~95mW blu-ray 8-) has a realy fat beam which makes it about the same brightness as a skiny 10mW 532nm. but.... when i get my camera out, bam!. all you can see is the 405nm with a tad of red or green in the background there.
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Old 10-24-2008, 02:57 PM #10
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Default Re: The eye's sensitivity to brightness *Read*

Also keep in mind that very few things in biology are linear. Twice the output could appear four times as bright, etc.
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Old 11-05-2008, 06:16 AM #11
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Default Re: The eye's sensitivity to brightness *Read*

Quote:
Originally Posted by Things
Think of this as a rule of thumb: To get 2X the brightness, you need about 4X the power!
thats a linear graph!!!! But i know that is just a generalization
also wouldn't the actual light be twice as bright but appear to our eyes as being a little bit brighter?
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Old 11-05-2008, 01:14 PM #12
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Default Re: The eye's sensitivity to brightness *Read*

Quote:
Originally Posted by carulli
[quote author=Things link=1221307975/0#0 date=1221307975]Think of this as a rule of thumb: To get 2X the brightness, you need about 4X the power!
thats a linear graph!!!! But i know that is just a generalization
also wouldn't the actual light be twice as bright but appear to our eyes as being a little bit brighter?[/quote]
No because brightness is defined as an attribute of our perception, so in other words: it's always as bright as you see it.It's relative to each of us and the way each of us perceive it, there is no "real" or "absolute" brighness that is constant and directly proportional to power. :P

This thread should really be called "The eye's sensitivity to power" *:P
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Old 11-05-2008, 01:43 PM #13
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Default Re: The eye's sensitivity to brightness *Read*

Sams Laser FAQ has a graph of sorts.
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Old 11-11-2008, 10:57 PM #14
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Default Re: The eye's sensitivity to brightness *Read*

Interesting, In my astronomy class I learned that the luminosity of a star is doubled with an increase of 4....so its most likely the same for a laser.
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Old 08-25-2009, 01:43 PM #15
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Default Re: The eye's sensitivity to brightness *Read*

My favorite way of intuitively understanding this sort of thing is looking at sound intensity.
A sound of 200dB will be incredibly unhealthy, probably fatal.
A sound of 50dB is roughly equal to moderate ambient noise, nothing loud, or even disturbing.

So, if you have four speakers, each playing soft music at 50dB, does that mean that your ears will bleed and you'll die? Of course not!

It's not really the same thing as the brightness of a laser, but I find it a useful guide for an intuitive understanding of the concept of a 'sort of logarithmic' function. =D

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EDIT: It was then that I realised that I'd posted in a thread I was reading out of interest. >_>
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Old 08-25-2009, 03:02 PM #16
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Default Re: The eye's sensitivity to brightness *Read*

I think my O-like 130-150 greenie is a lot brighter than my Ledshoppe 50.
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