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What power will allow a visible beam?

WhiteFang

WhiteFang

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For a standard 650 nm red laser, what's the general rule for power necessary to produce a visible beam? I'm not talking a lightsaber, just something that will distinguish it from a dog toy. I'm very skeptical of buying 30mW for a build and being able to see the difference.
 





Hello WhiteFang,

Everyone's eyes are different so people will pick up different laser beams differently. Some people here have noticed not being able to see 5mW's of a standard 650nm red (beam)while I could see 3mW's of 650nm(beam). As a general rule, 5mW's of 532 would produce a somewhat visible beam. Not anything amazing but something you'd be able to see in the dark. Using the following tool: Relative Laser Beam Brightness Calculator: (532nm 5mw) vs. (650nm 93.64mw) it looks like you'd need about 90mW's or so. :yh:

-Alex
 
Last edited:
Hap said:
Hello WhiteFang,

Everyone's eyes are different so people will pick up different laser beams differently. Some people here have noticed not being able to see 5mW's of a standard 650nm red (beam)while I could see 3mW's of 650nm(beam). As a general rule, 5mW's of 532 would produce a somewhat visible beam. Not anything amazing but something you'd be able to see in the dark. Using the following tool: Relative Laser Beam Brightness Calculator: (532nm 5mw) vs. (650nm 93.64mw) it looks like you'd need about 90mW's or so. :yh:

-Alex
Click to expand...

Thank you!

And I'm using this for a small build, not for a pet. Reds seem to be built much smaller than the rest, and much cheaper to acquire, so I was just wondering how much power I'd need :D
 
WhiteFang said:
Thank you!

And I'm using this for a small build, not for a pet. Reds seem to be built much smaller than the rest, and much cheaper to acquire, so I was just wondering how much power I'd need :D
Click to expand...

650nm reds are smaller and cheaper since they use a mass produced diode for the wavelength desired. Anything DPSS will be more expensive(relatively, 532nm somewhat) and wouldn't be as small as a diode since you need crystals installed to get the wavelength you want! :)

-Alex
 
Don't expect to see the beam at 30mw at that wavelength, unless you kick up some dust in the room and it is very dark.
 
You need to go down to ~635nm if you want to see the beam at low powers like that, 650nm really just doesn't have the visibility. I can see the beam from my HeNe just fine at 6mW, 632.8nm.
 
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I'd go with an LPC-826, LPC-836 or an LPC-840. These can be pushed to 400 mW and I can see the beam fine at that power or even lower. They are all less than $10.00 each and can be found everywhere on eBay.
 
It depends on how clean the air is too.

In a smokey room even a 5 mW 650 nm laser will produce a visible beam, but in cleaner air much larger power levels will be required.

In pure air, with no particles floating around etc, you can see a beam only due to scattering at a molecular level. This effect is -very- small. If you were standing in a well lit cleanroom there could be a 10 watt green beam passing a meter in front of your eyes without you noticing it at all, since there is nothing 'big' in the air to scatter that light and ambient light is so bright it will swamp out any molecular level scattering easily.
 
Benm said:
It depends on how clean the air is too.

In a smokey room even a 5 mW 650 nm laser will produce a visible beam, but in cleaner air much larger power levels will be required.

In pure air, with no particles floating around etc, you can see a beam only due to scattering at a molecular level. This effect is -very- small. If you were standing in a well lit cleanroom there could be a 10 watt green beam passing a meter in front of your eyes without you noticing it at all, since there is nothing 'big' in the air to scatter that light and ambient light is so bright it will swamp out any molecular level scattering easily.
Click to expand...

I need a cleanroom with 1064nm qswitched to 100W 532nm.
 
Also depends if observed in night or daylight, when comparing beams - here one of my recent post, when discussing this - luminosity function = how is a given wavelength perceived by human eye:

Radim said:
Here it is for example:


(click the image for source)

I think it approximates a beam as well. However blue light is diffused more in the air (that's why sky is blue and sunsets/sunrises red). Some time ago I've made some simple excel model for that used luminosity function values I found on internet to calculate estimates of various danger distances of my lasers (like flashblindess hazard distance). I might find it and put the source of the website I used if you like.
Click to expand...
 
Hap said:
Hello WhiteFang,

Everyone's eyes are different so people will pick up different laser beams differently. Some people here have noticed not being able to see 5mW's of a standard 650nm red (beam)while I could see 3mW's of 650nm(beam). As a general rule, 5mW's of 532 would produce a somewhat visible beam. Not anything amazing but something you'd be able to see in the dark. Using the following tool: Relative Laser Beam Brightness Calculator: (532nm 5mw) vs. (650nm 93.64mw) it looks like you'd need about 90mW's or so. :yh:

-Alex
Click to expand...

Alex I've been looking for this damn relative beam calculator forever! lol I used to have it saved to my old iPhone until I got a new one and forgot what to look up. Thanks :)
 
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