Laser beam brightness vs wavelength: Seeking personal experiences

[Spoomples]

I've been using the relative laser brightness calculator to figure out how beams at different wavelengths compare, but I've started to have some doubts about its accuracy. It says that 100-200mw of 650-660nm red should equal 5mw of 532nm green (for me, the red is much dimmer), and that a 50mw 405nm beam should be 7-10x less visible then the same red laser as before (for me, the violet is at least as visible as the red). I've looked through the forums to try and better data, but I've had little luck in finding hard numbers. So, in light of all that, I decided to come here and directly ask members about their personal experiences, and hopefully get enough data to create slightly better model.

The question: Given the exact same viewing conditions (background lighting, air quality, viewing angle, etc), how many mw of one wavelength does it take to match (X)mw of another? This question is specifically about the beam, not the dot.

Small details about the testing conditions and the beam diameters may be useful, but they are not required.
The ideal comparison would be in a dark room with clean air against a 532nm laser with a known power output, but that is also not required. Any wavelength can be compared to any other.

 

[CurtisOliver]

The reasons why calculators like that struggle is that it doesn’t account for varied observational conditions.

Here are some points I can think of on the top of my head that will throw of its accuracy.

1. The observer: Every individual observes light slightly differently. For example, some on here say they can see 405nm clearly like you would 450nm. Others say the dot is blurry, including myself. Also, we have had discussions here in the past about our ability to see near-IR light. Some can see IR light more than others. This means that the brightness levels across the visible spectrum will differ for these individuals. Not by much, but a slight difference regardless.
2. Lighting levels: Many seem to forget that the data behind these calculators come from actual luminous efficacy research. And that the two sets of data are set out at the extremes of human vision. Scotopic vision is typically defined as being around 0.001 lx - 0.000001 lx. This is the equivalent of being in a area with no light pollution or moonlight, and your eyes are fully adjusted to darkness. A typical room in darkness may appear dark, but in comparison it isn't actually dark enough to be considered truly scotopic. Also even it if was, you must allow night vision to kick in before observing any visible wavelengths. An important thing to consider, is that observing any luminous wavelength whilst in scotopic conditions can actually bring you out of those conditions. This is why astronomers observing the faintest stars use red light to look at their star maps. This is because it is bright enough to see what you are doing, but doesn't ruin your night vision. Photopic vision follows the same guidelines but at the opposite end of the scale. I've seen data suggest that photopic conditions start as low as 10 lx, but in reality the data would of been recorded at a much higher lux level. 100000 lux is more realistic as it is equivalent to full daylight. Direct sunlight being 130000 lx. The point I'm making is that your test conditions are most likely are not anywhere near either of these data sets. There is a lesser known band called Mesopic, but you won't get any data for it. But all it is, is a middle ground. I have created data myself for another three bands, of which I've labelled for simplicity sake, Mesopic, Meso-scotopic, and Meso-photopic. See the picture at the bottom.
3. Power and beam specs: For the sake of a fair test, the power must be known for both lasers, they don't have to be identical, but it would obviously help. That factor is obvious, the one that isn't though is the lasers beam specs. A smaller spot size, tighter beam, a single mode Gaussian output etc all makes a difference in how we perceive a lasers dot and beam brightness. Rayleigh scattering is accounted for however.
4. Atmospheric conditions: You've already mentioned this, but calculators don't account for particulates etc.

If I think of any more points, i'll add them.

You will struggle to build a better calculator without making it incredibly difficult to use. These calculators are more than adequate for our basic needs. The only way to improve upon them would be if you started to ask for lux levels, beam size etc

 

[steve001]

I've been using the relative laser brightness calculator

What the other poster wrote. Sam's Laser FAQ has within its many pages of laser info shows a chart of sorts detailing the visual response humans show at various wave lengths across the visible spectrum. The response is a bell curve with 555.5 nm being the peak sensitivity.

 

[kecked]

I find for myself 575 is brighter for me than 565. Try it by eye and see what works for you. It also changes for me by the day. In daylight vs night. Moisture, dust, mood, phase of the moon....ambient b@ckground. Size of the beam. It’s not linear to your eye either.

 

[CDBEAM777]

WOW....Some GREAT information !!! Thank you ! SHOULD be made a Sticky !!!.....Hmmmmm....The Takeaway......Any of the Relative Luminosity Calculators....are basic / simplistic ! The real world and the human eye.....are a great deal more complicated !! Variations explained !!! THANX !!
CDBEAM

 

[paul1598419]

Unless you own a laser power meter you probably won't know the actual power of your lasers. That is also an issue when comparing wavelengths for visibility.

 

[Alaskan]

I suppose it depends on some variables, are you talking about the spot, or the beam. If a spot is it reflecting off of a material which reflects some wavelengths, i.e., lower or higher, better than others? Also, some individuals have eye sensitivity biased more sensitive for some wavelengths than others. I just use that brightness calculator as an approximation. As Curtis already remarked, much can be about the observational variables, the power density, the beam or spot diameter etc. also factor in.

 

[Spoomples]

All the counterpoints are fair, I suppose this problem would have been solved a while ago if it was simple. I would still still appreciate personal anecdotes though, as I won't have the required measurement tools or a full range of wavelengths and powers for quite some time. Good LPMs cost a pretty penny.

 

[CurtisOliver]

Here’s the thing, you can’t improve upon the accuracy of a calculator using stories/anecdotes instead of scientific measurements. Our eyes are not great at accurately comparing visual intensity. Humans are incredibly perspective based. The level of inaccuracy can never improved by collective observations. One person can say a laser is brighter than another. The other person can have the same model lasers and disagree. And even if they did agree, how do you define by how much?

 

[paul1598419]

I got my first LPM from a member here for $100. It was a Laserbee 3.2 watt one. Shortly after that purchased an X4 Radiant 3.7 watt LPM new for $110 and it is still working just fine. I have several working LPMs now.

 

[hakzaw1]

Lots to study at Sam's Laser.
Skimming will not do much good.

No two 'nm' comparisons will be the same. yet all are valid.


it is a trade-off---..
I can lend you a meter BUT NOT if I do not know more about you.

 

[Spoomples]

I thought I did make an intro post? And I'm not too interested in borrowing equipment. It seems like it would be less of a hassle to just save up for a while and buy one outright.

And on the original topic, I made this to try and get more accurate values.


key:
r = relative beam brightness of wavelength 1 vs wavelength 2,
V' = scotopic weighting function, V = photopic weighting function, x = luminance-based weighting factor

The equation was made using these sources:
https://en.wikipedia.org/wiki/Mesopic_vision https://en.wikipedia.org/wiki/Rayleigh_scattering

Assuming the luminance of the area is 0.1 cd/m2 (A bit darker then the minimum residential streetlights need to provide) and an x value of .3, a 532nm beam would be 104x brighter then a 660nm beam, and 24.9x brighter then a 405nm beam.
In other words, these lasers would have a similar beam brightness:
5mw 532nm, 521mw 660nm, 124mw 405nm

Those values seems closer to my personal observations then the calculator's answer.

note: I was aware of luminosity functions and Rayleigh scattering before asking asking the original question, but asking for personal experiences seemed like the more direct route.

 

[Alaskan]

For the same amount of power and all things being equal (which for lasers at such different wavelengths, likely will not be equal) I consider 450 nm blue to be 10% as bright to the eye as 532 nm green, and 650 nm red the same, about 10% as bright too. Mind you, this is a rough approximation because we can't really tell the difference by eye to anywhere close to exact percentages, not even within a margin of error of 20% by eye, some say they can only markedly tell the difference if the power is halved, or doubled.

At the extreme ends shorter than blue into violet before UV, and beyond 650 nm red approaching IR, the sensitivity of our eyes drop off very rapidly. For example, I consider short wavelength 405 nm violet to be about 1 percent as bright as 532 nm green at the same power level. For long wavelength 670-680 nm deep red the same thing, very dim.

So, there is my rough approximation.

 

[paul1598419]

If you could measure the power of lasers more indirectly it would have been done long before now. You aren't going to reinvent the wheel.

 

[Bolt Thrower]

Here’s the thing, you can’t improve upon the accuracy of a calculator using stories/anecdotes instead of scientific measurements. Our eyes are not great at accurately comparing visual intensity. Humans are incredibly perspective based. The level of inaccuracy can never improved by collective observations. One person can say a laser is brighter than another. The other person can have the same model lasers and disagree. And even if they did agree, how do you define by how much?

Hay sparkies , I'm new on board . I'm really getting some good input here cheers.. Good logic of comparison there , as to how someone with seeing eye glasses would absorb the laser spectrum as apposed to someone without .. similar individual personal visual theory's I guess . Would it differ between the two

 

[steve001]

I thought I did make an intro post? And I'm not too interested in borrowing equipment. It seems like it would be less of a hassle to just save up for a while and buy one outright.

And on the original topic, I made this to try and get more accurate values.

View attachment 64965
key:
r = relative beam brightness of wavelength 1 vs wavelength 2,
V' = scotopic weighting function, V = photopic weighting function, x = luminance-based weighting factor

The equation was made using these sources:
https://en.wikipedia.org/wiki/Mesopic_vision https://en.wikipedia.org/wiki/Rayleigh_scattering

Assuming the luminance of the area is 0.1 cd/m2 (A bit darker then the minimum residential streetlights need to provide) and an x value of .3, a 532nm beam would be 104x brighter then a 660nm beam, and 24.9x brighter then a 405nm beam.
In other words, these lasers would have a similar beam brightness:
5mw 532nm, 521mw 660nm, 124mw 405nm

Those values seems closer to my personal observations then the calculator's answer.

note: I was aware of luminosity functions and Rayleigh scattering before asking asking the original question, but asking for personal experiences seemed like the more direct route.

There's no need to reinvent the wheel. Check Sam's Laser FAQ for the perceived sensitivity by wavelength chart.