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# looking to buy brightest diode laser.

#### Encap

##### Well-known member
I definitely believe it. The beams on my 85mw 520 and my 740mw 445 look almost the same, brightness wise. The dot on the 520 is probably actually brighter.
That you need 4 times the power to perceive ~ double the brightness applies only to same wavelength.

That makes sense. Blue wavelengths scatter more easily than green, hence why the sky is blue. That explains why the beams appear the same brightness and the dots don't.
Human visual perception is a complicated thing/topic. Here is a tip of the iceberg chart of topics: http://hyperphysics.phy-astr.gsu.edu/hbase/vision/visioncon.html#c1

Scattering is one part of it, but it also has to do with how your eyes perceive the brightness of certain colors. Take a look at this table to understand how your eyes will perceive the brightness of a light source as a function of wavelength. here: Luminous Efficacy

You can compare different wavelengths of same or different output power with this tool programed by an LPF member rhd in 2011. t uses CIE table values. Raleigh Scattering is factored in if you choose "beam". here: Relative Laser Beam Brightness Calculator: (532nm 1000mw) vs. (445nm 1000mw)

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#### green lasers rock

##### Active member
That you need 4 times the power to perceive ~ double the brightness applies only to same wavelength.

Human visual perception is a complicated thing
Scattering is one part of it, but it also has to do with how your eyes perceive the brightness of certain colors. Take a look at this table to understand how your eyes will perceive the brightness of a light source as a function of wavelength. Luminous Efficacy

You can compare different wavelengths of same or different output power--It uses CIE table values. Raleigh Scattering is factored in if you choose "beam". here: Relative Laser Beam Brightness Calculator: (532nm 1000mw) vs. (445nm 1000mw)
I commonly sight that calculator for brightness comparisons, but I have started to loose faith in it. According to it, a 100mw 450nm and 200mw 650nm should have the same beam brightness, and the red should have a much brighter dot, but when i tried my 100mw 450 and 200mw 650, I discovered this was absolutely not true. The blue beam is way brighter, and the blue dot is also brighter than the red. I think the brightness of blue lasers is underestimated.

#### Atomicrox

##### Well-known member
For starters it's likely your 650nm is actually 660nm, that does quite a bit of difference. The CIE table it uses is known to underestimate low wavelength brightness (not that much for blue but a LOT for violet). It's still the best scientifically acquired data available, AFAIK, and it does a decent job for most common visible lasers except for 405nm.

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#### Pman

##### Well-known member
I think the issue is that divergence isn't taken into account. The calculator may be correct but when you try and compare 2 different wavelengths yourself for brightness it's not so easy as there's very little chance that their divergence will be the same. I would try both focusing them at infinity and then try it again with the lenses removed.

#### green lasers rock

##### Active member
Doesnet peak visibility shift to around 500nm in darkness? That would explain why the blue looks so much brighter than the red.

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#### diachi

##### Well-known member
Doesnet peak visibility shift to around 500mw in darkness? That would explain why the blue looks so much brighter than the red.
nm* - and yes it does.

#### CaliKirk

##### New member
GLR- I just got my 1.2w 532 from XPL and damn is it bright! The only thing that sucks is that the driver on myne moves so much causing the push button to stick and I have to immediately send it back to Hong Kong for repairs. At this point with the extra shipping costs I would have been better off going the 1w+ 520 route..

#### Rivem

##### Well-known member
nm* - and yes it does.

Whether or not that means something for lasers is highly questionable though.

Scoptic vision (the shift for night vision) fundamentally means you'd have little to no color perception.

Considering you can see the color of laser beams fairly easily, you're very likely to be using photoptic vision which trumps any scoptic vision you might have.

405nm definitely seems to get WAY brighter when dark adapted though.

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#### Encap

##### Well-known member
For starters it's likely your 650nm is actually 660nm, that does quite a bit of difference. The CIE table it uses is known to underestimate low wavelength brightness (not that much for blue but a LOT for violet). It's still the best scientifically acquired data available, AFAIK, and it does a decent job for most common visible lasers except for 405nm.
Excellent point--the relative brightness tool shows 450nm 100mW being brighter than 200mW at 652nm through 660nm plus the actual output of those lasers in both mW and nm are unknowns --as are the diameter and divergence/power density of each unknown --as are the particles in the atmosphere when the comparison was made.
As one member put it:
"Basically, I think it's almost impossible to accurately determine the brightness of the BEAM
without considering the size of the particles on the air.
Which will never be the same twice. So all you can hope for is a good aproximation.are the size of particles in the atmosphere and so on."

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#### diachi

##### Well-known member
Whether or not that means something for lasers is highly questionable though.

Scoptic vision (the shift for night vision) fundamentally means you'd have little to no color perception.

Considering you can see the color of laser beams fairly easily, you're very likely to be using photoptic vision which trumps any scoptic vision you might have.

405nm definitely seems to get WAY brighter when far adapted though.
Of course - may not work at all that way with lasers. Certainly in low light conditions it'd make sense (light moon light or some such) that your sensitivity shifts to the blue, but I don't imagine it'd make much of a difference for intense light such as laser beams as you say. Was really just answering the question "does the peak sensitivity of your eye shift at night?" (paraphrased...).

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#### Rivem

##### Well-known member
Of course - may not work at all that way with lasers. Certainly in low light conditions it'd make sense (light moon light or some such) that your sensitivity shifts to the blue, but I don't imagine it'd make much of a difference for intense light such as laser beams as you say. Was really just answering the question "does the peak sensitivity of your eye shift at night?" (paraphrased...).
Not disagreeing with you pal. Just adding the "YMMV/with a grain of salt" statement.

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#### diachi

##### Well-known member
Not disagreeing with you pal. Just adding the "YMMV/with a grain of salt" statement.
I know, wasn't trying to argue! Sorry if it came off that way :beer::beer:

#### Encap

##### Well-known member
Of course - may not work at all that way with lasers. Certainly in low light conditions it'd make sense (light moon light or some such) that your sensitivity shifts to the blue, but I don't imagine it'd make much of a difference for intense light such as laser beams as you say. Was really just answering the question "does the peak sensitivity of your eye shift at night?" (paraphrased...).
"There is one glitch with the scotopic curve where lasers are concerned, however - it is rather unlikely for a person to view a typical laser beam using scotopic vision!

In fact, I can't remember EVER viewing a laser beam with scotopic vision!

Here's a big hint...if you can even vaguely tell what color the laser beam is, then you are not seeing it with scotopic vision!

What you are using when you view a laser beam under subdued or nighttime conditions (but can still tell what color it is), is mixed-mode vision (both rods & cones active).
In this case, the response curve is the combination of both the photopic and scotopic curves! The relative ratio of each will depend on how active each visual system is - the darker it is, the more it will shift away from photopic and towards scotopic.
Also, due to the much greater sensitivity of the rods vs the cones, once it gets dark enough for the rods to start kicking-in, you will see a definite shift in the peak response towards blue, due to the rod sensitivity peaking at ~505nm."
From this excellent thread post #29 here: http://laserpointerforums.com/f44/new-tool-calculate-relative-brightness-wavelengths-nm-61238-2.html

In post #30 rhd who created the relative brightness too says: " The reality is that S vs P vision isn't about day or night, it's largely about light intensity. A visible laser beam is going to be high intensity light, even in dark environments."

rhd also points out: Anyway, it is what it is. This tool is basically ONLY a tool for easily applying relative sensitivity curves, with optional Raleigh scattering. Nothing more." in post# 53

#### green lasers rock

##### Active member
yes that makes sense. If you can see the beam color, you are not seeing with only rods. And when I say i'm looking for the brightest beam, I mean the brightest beam in a set atmospheric condition. For example using a 7 watt 445 and a 1 watt 520 outside at the same time on the same night and seeing which one is brighter. Is it possible for the green laser to overtake the blue one night, but the reverse happen on another even when the lasers are being used at the same time. Do certain conditions bring out certain wavelengths more than others?

#### Encap

##### Well-known member
yes that makes sense. If you can see the beam color, you are not seeing with only rods. And when I say i'm looking for the brightest beam, I mean the brightest beam in a set atmospheric condition. For example using a 7 watt 445 and a 1 watt 520 outside at the same time on the same night and seeing which one is brighter. Is it possible for the green laser to overtake the blue one night, but the reverse happen on another even when the lasers are being used at the same time. Do certain conditions bring out certain wavelengths more than others?
The imaginary lasers in your question don't exist in the real world--even if they did they are just outputting 1W of green and 7 W of blue both of which produce exactly the same brightness beam in a vacuum----no beam at all/zero brightness.
Start from there and attempt to understand and explain what is going on in any case other than that one---all the many parameters that actually matter defined and specified/nailed down

When you start talking about "subjective" brightness values (i.e. - looks brighter), you also need to take eye's brightness response curve into account--human eye has a logarithmic rather than linear response to light-is the point--It is your eyes response and brain that perceive a beam based upon brightness of different wavelengths/different energies reflected back to your eyes by particles in the atmosphere which reflect or scatter different wavelengths and energies at different rates depending upon sizes and number of particles or molecules present.

I know you are only 14 but the only answer can be---why beat a dead horse any more than you have already --just go do it and see in the real world what is what. Everything else is just daydreams as playtime entertainment of little "real" value at all at best .

#### green lasers rock

##### Active member
The imaginary lasers in your question don't exist in the real world--even if they did they are just outputting 1W of green and 7 W of blue both of which produce exactly the same brightness beam in a vacuum----no beam at all/zero brightness.
Start from there and attempt to understand and explain what is going on in any case other than that one---all the many parameters that actually matter defined and specified/nailed down

When you start talking about "subjective" brightness values (i.e. - looks brighter), you also need to take eye's brightness response curve into account--human eye has a logarithmic rather than linear response to light-is the point--It is your eyes response and brain that perceive a beam based upon brightness of different wavelengths/different energies reflected back to your eyes by particles in the atmosphere which reflect or scatter different wavelengths and energies at different rates depending upon sizes and number of particles or molecules present.

I know you are only 14 but the only answer can be---why beat a dead horse any more than you have already --just go do it and see in the real world what is what. Everything else is just daydreams as playtime entertainment of little "real" value at all at best .
I am talking about comparative beam visibility in conditions where particles exist to scatter light, I know there is no beam from even the strongest of lasers in a matter free environment as with no matter to scatter light, a visible beam can not exist. I also mean the comparison of two lasers in exactly the same atmospheric conditions at the same time, not at different times. If the conditions are the same, the brightness can be compared. I know there are many facts that could create differing results, but i'm not looking for an exact answer, what I want to know is generally speaking what handheld diod elaser will have a beam brighter than all others when particles in the atmosphere exist to scatter light. So not lasers being seen in different conditions, imagine comparing all handheld lasers at the same time outside during the same night where the conditions the lasers are in are identical. With identical scattering conditions, the brighter beam would be obvious. This is what i am looking for. Of course, the ultimate solution would be for me to test out many lasers and see for myself, but unlike the vets I dont have the resources to perform such experiments. Someday