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Visibility of 1W vs 2W or 3W

BodhiSci

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I see lot's of posts comparing different colored and powered lasers, but not much on those of the same color.

I don't think that doubling power doubles subjective brightness. The human eye doesn't seem to work like that, a 1W laser is prob not twuice as bright as a 500mW.

I wish someone had made a visibility curve. Perhaps I will someday when my collection is bigger.
 

Teej

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I see lot's of posts comparing different colored and powered lasers, but not much on those of the same color.

I don't think that doubling power doubles subjective brightness. The human eye doesn't seem to work like that, a 1W laser is prob not twuice as bright as a 500mW.

I wish someone had made a visibility curve. Perhaps I will someday when my collection is bigger.
Wattage is not the only variable when looking at same wavelength dots. The size of the dot at a given distance will also make a large difference for example.


SUBJECTIVE brightness (by eye) is frustratingly poor, as the human eye is a lousy light meter.


The intensity (brightness) of the dot is measured in lux. Generally, for say a flashlight's spot, you might be able to discern as little as a 5% change in lux when the intensity is lower, but, as the intensity starts to stop down the eye and glare is perceived, if the dot is the same size, sometimes no amount of additional intensity is observed.

IE: Once you've "pegged the needle of your eye's light meter", that's it...it all looks the same.

If the brighter dot also looks larger, THEN the eye perceives the additional brightness.

As most surfaces the dot is likely to be on, in common use, will reflect some of the light, there will be a tendency for the perceived dot size, when glare has been achieved, to grow...due to perception of the surrounding reflected light to the sides of the dot, etc.


The other question is whether the wattage and the output are in a 1:1 ratio.

For example, a driver for one range might have a different efficiency...so, 2 watts into one , and 4 watts into the other, may not have the same ratio in output.

And so forth.
 

BodhiSci

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Ok, thanks but I'm really not any closer to having an idea of how much a 500mW, 1W, 2W, or 3W might compare to each other. It is good info though, glad to know it and it is for sure related.

Let's just say pointing into the sky at night time. What about then, does a 1W seem alot brighter than a 500mW, same for 2W and 1W. I'm talking output, not input into the laser.

I don't expect people have those 3 lasers in the same color, but they might have something that would be comparable.

I
 
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With my two 445nm lasers one is approximately double the strength of the other and when viewing the beam only and not the dot there is a huge difference in brightness. Of course the brightness of the beam itself is dependent on the amount of particulate matter in the air as well as the size or power density of the beam.

Alan
 

rusirius

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With my two 445nm lasers one is approximately double the strength of the other and when viewing the beam only and not the dot there is a huge difference in brightness. Of course the brightness of the beam itself is dependent on the amount of particulate matter in the air as well as the size or power density of the beam.

Alan
Agreed. You can definitely notice a difference in the dot, but one of the big places I notice is the beam itself. If I run an M140 at say 500mW, you can just barely see the beam in a lit room. If I run it at 2W the beam is pretty much a solid very bright beam, even in normal lighting.
 

DTR

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With 445nm I have always figured about 4X the output power to be 2X as visually bright. May not be exact or even how every eye sees it but seems to be pretty close to how my eyes see it.:beer:
 

BodhiSci

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Very good stuff! Exactly what I needed to know plus some :wave: Thank you much.

I went on a walk today and the dot does have an effect on perceived brightness. Beam is what I'm all about though!

I'm sure future lzrpeeps will appreciate it too.
 
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Teej

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With 445nm I have always figured about 4X the output power to be 2X as visually bright. May not be exact or even how every eye sees it but seems to be pretty close to how my eyes see it.:beer:
This is probably correlating with the inverse square law.

If we are only talking about the beam, instead of the dot, the beam brightness can be dim enough to not glare, and allow the eye to at least do a rough metering of the brightness.
 
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The dot will stop appearing brighter
because the eye has reached a type of
saturation and 1-3W will all look
prettymuch the same.

Where you will notice a difference is on
nearby objects. A 1W 450nm dot on a white
surface will dimly light a room. A 4.5W
450nm dot will light up the whole room and
dimly light adjacent rooms.

Now the beam is where you will really
notice the difference because it falls in a
range where eyes are fairly sensitive.
Again, using 450nm as an example, 1W is
visible, 2W is very visible, and 3W+ is
unmistakable.
 

Atomicrox

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That differs from my experience. My 3W (beam) looks brighter than the 1.2W, but not by that much. Makes more difference sideways, though. To me it seems increasing power at lower powers makes far more difference than at higher powers.
 

BodhiSci

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That differs from my experience. My 3W (beam) looks brighter than the 1.2W, but not by that much. Makes more difference sideways, though. To me it seems increasing power at lower powers makes far more difference than at higher powers.
Are they the same size? The power density that Pi R Squared mentioned might be a factor. I imagine diff wavelengths might be vary in how they follow these trends. A 650 might be diff than a 450 nm.

Will have to play with variable power outside in the future.
 

Teej

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That differs from my experience. My 3W (beam) looks brighter than the 1.2W, but not by that much. Makes more difference sideways, though. To me it seems increasing power at lower powers makes far more difference than at higher powers.



It can also be due to the a fore mentioned stop down, as, once the eye measures a certain level of brightness, additional brightness is all after your eye's light meter has already been pegged.

IE: The lower the intensity, the more range is left before the needle is pegged, etc.

Looking at the beam from the side is going to avoid as much of the bounce back that increases glare, such as when looking at the dot, etc....similarly leaving some meter range for the eyes.

Eyes are lousy at subjectively judging brightness in general. According to my tests at least, they seem to be least challenged when the sources are not TOO bright, and, they can do side by side comparisons.

If I show a light to a subject, ask them to rate its brightness, and then show them the same light the next day...asking the same question, the answers are all over the place...especially if they are conditioned differently before hand (night adaptation level, etc).

If I simply make the same light brighter/dimmer while they see its intensity change, as little as a 5% change is observable....but if one intensity is on, there's a pause, and then a different intensity, even if the time gap is mere seconds...the percent change will widen by a LOT, closer to 25% being needed to be sure it went brighter or dimmer for example.

If the time gap widens, so does the range of perception, so that even orders of magnitude can be misjudged.
 
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Atomicrox

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Are they the same size? The power density that Pi R Squared mentioned might be a factor. I imagine diff wavelengths might be vary in how they follow these trends. A 650 might be diff than a 450 nm.

Will have to play with variable power outside in the future.
The diodes have similar divergences but the 3W is a bit worse because of the G lens.

That said I don't think power density makes as much difference as many here say. Brightness doesn't change much if I defocus the laser just a little.

It can also be due to the a fore mentioned stop down, as, once the eye measures a certain level of brightness, additional brightness is all after your eye's light meter has already been pegged.

IE: The lower the intensity, the more range is left before the needle is pegged, etc.

Looking at the beam from the side is going to avoid as much of the bounce back that increases glare, such as when looking at the dot, etc....similarly leaving some meter range for the eyes.

Eyes are lousy at subjectively judging brightness in general. According to my tests at least, they seem to be least challenged when the sources are not TOO bright, and, they can do side by side comparisons.

If I show a light to a subject, ask them to rate its brightness, and then show them the same light the next day...asking the same question, the answers are all over the place...especially if they are conditioned differently before hand (night adaptation level, etc).

If I simply make the same light brighter/dimmer while they see its intensity change, as little as a 5% change is observable....but if one intensity is on, there's a pause, and then a different intensity, even if the time gap is mere seconds...the percent change will widen by a LOT, closer to 25% being needed to be sure it went brighter or dimmer for example.

If the time gap widens, so does the range of perception, so that even orders of magnitude can be misjudged.
I think this is more like it. Our eyes adapt to make a wide range of brightness levels "meaningful" and that throws off any attempts to "eyeball" brightness.
 




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