perceived brightness for given wavelength?

I remember seeing a chart somewhere, though I may be mistaking it for something else.

I know beam diameter and divergence affects this a lot too.

Anyway, same power blue laser (445nm) appears less bright to the human eye than red and green wavelengths.
Is there anyway to find out how bright each wavelength appears to the human eye, or how their brightness compares?

Say you want to compare 445nm, 638nm and 520nm.

You were probably thinking of this:

http://http://users16.jabry.com/lsrtools/RelativeBrightness/

Although, it's not up and running right now.

Edit: Teej, and Pi have a working version posted!

iroquois said:

I remember seeing a chart somewhere, though I may be mistaking it for something else.

I know beam diameter and divergence affects this a lot too.

Anyway, same power blue laser (445nm) appears less bright to the human eye than red and green wavelengths.
Is there anyway to find out how bright each wavelength appears to the human eye, or how their brightness compares?

Say you want to compare 445nm, 638nm and 520nm.

Click to expand...

Yes there is such a chart somewhere, at least 2 different ones, can't remember where just now. Someone should come along and post that info here shortly.

No blue isn't less bright than red for the same power level. They are about the same. The peak brightness is somewhere about 550nm, I don't remember exactly, green lasers are the brightest.

So if you compare 445nm and 638nm they are very close in brightness, but a 520nm is very much brighter. Even my 82mw 520nm has a visible beam.

Alan

Edit: found them.

This one is good.
http://lsrtools.1apps.com/relativebrightness/

And here is something but not so detailed.

Try this:

Beam: (580nm 1mw) vs. (595nm 1mw)




You just plug in the wavelength and power, etc....and you get a comparison.

Teej, Pi, thanks, it's nice to see a version of that calculator tool that is working. The one I had been using hasn't been up for a while.
I find it pretty handy to have around for general comparisons, although some have said it's not always accurate.

Thanks guys.
The only problem I see with the online tools it seems to work fine comparing different wavelengths of same power, but comparing different power of the same wavelength doesn't seem right. 10mW compared to 100mW or 100mW compared to 1000mW of anything says 10x more bright.
I remember someone saying brightness doesn't increase linearly or the same amount as the power increases, more like something like twice as bright if 3 times more power, or something.
Although I might not be remembering it right and these values are about how far the visible beam will travel before fading.

iroquois said:

I remember someone saying brightness doesn't increase linearly or the same amount as the power increases, more like something like twice as bright if 3 times more power, or something.

Click to expand...

Yes, I've heard similar values also; many times, I've heard that 4 times power is needed for twice the perceived brightness.

Its along the lines of the inverse square law...but, for watts, if you think about it along the lines of lux vs lumens for example, for a given source with all else being equal, twice the lumens will give twice the lux.

Lux is how bright it looks, and lumens would be the total output.

Does that help?


The 4x as bright to look 2x as bright is more along the lines of distance relationships, and is according to the inverse square law.


Example:

I have a flashlight that puts out 1,000 lumens at 100,000 cd (Lux at 1 meter equivalent).

That means at 100 meters, it will put 10 lux on my target.

If I made that 2,000 lumens with the same beam pattern, I would now have twice that, at 20 lux (Double the lumens per square meter).

If I kept the 1,000 lumens and 100,000 cd, but moved the target to 200 meters, I would drop to only 2.5 lux.

So at double the DISTANCE, the same light is going to make the target appear 1/4 as bright.


And, conversely, the light would need to be 4x brighter to make the target look the same brightness, at double the distance.