Welcome to Laser Pointer Forums - discuss green laser pointers, blue laser pointers, and all types of lasers



Laser vs. lamp. I've never heard a sensible answer to this. Help!

adam1128

New member
Joined
Jun 1, 2018
Messages
8
Points
1
Imagine I have a lamp (incoherent light - lets say it's a consumer projector), and a class 2m laser device, and both have identical divergence and identical waist width, and are kicking out the same radiant flux, all in the visible spectrum (say around 532nm).

My question: In this case, is the laser more dangerous than the projector? Why?

=====Background info=====

I often hear that the laser will be more dangerous because the light is coherent. But when I ask why, I often hear that coherence means you can focus the beam to a smaller point. But when we're already dealing with a beam that isn't focused to a point, I don't see why that would make any difference. I'm sure I'm missing something, I just don't know what!

=====Why I care=====
I care because I'm working on an invention that needs a very bright light source with a similar divergence and waist with as a consumer projector, but that needs to be a very narrow wavelength. Because of the narrow wavelength requirement, I've opted for a laser. I've done experiments with something like a laser genetics ND3, which works well, but isn't bright enough, and my concern is that if I go much brighter, it will exceed the limit for a 2m laser (which is not an option - the invention will be a consumer device). The ND3 is a 2m laser with a 40mw diode. Assuming that a 532nm diode creates ~600 lumens per watt, that equates to about 24 lumens, which isn't much. On the other hand, a laser projector (which as I understand it uses a diffuser to make the laser light incoherent) can be 10,000 lumens and still be in risk group 2, which approximately equates to class 2m for lasers (i.e. there's no risk of eye damage due to aversion responses). The ND3 has a similar size lens that the light escapes from as a projector, and a similar divergence. If you put your eye right up to the projector, or the ND3, it seems to me there wouldn't be much difference in terms of the % of the total beam entering your eye, and the divergence of that beam - only the projector is 10,000 lumens, and the ND3 is 24. Does that mean I could have a 10,000 lumen version of the ND3 and it still be class 2m?

Obviously if I opted for a more traditional light source, then I'd have to filter it down to a narrow wavelength, and throw most of the light away - but if I did this instead, would it be safer than the laser version? If so, why?

Finally, if there is some reason why laser light is inherently more dangerous than the same flux level of 'normal' light, is there some way to remove this without altering the wavelength?

Sorry about all the questions, and thanks - I'm a real beginner so any help would be amazing!
 



steve001

Well-known member
Joined
Jun 3, 2007
Messages
2,471
Points
113
Imagine I have a lamp (incoherent light - lets say it's a consumer projector), and a class 2m laser device, and both have identical divergence and identical waist width, and are kicking out the same radiant flux, all in the visible spectrum (say around 532nm).

My question: In this case, is the laser more dangerous than the projector? Why?

=====Background info=====

I often hear that the laser will be more dangerous because the light is coherent. But when I ask why, I often hear that coherence means you can focus the beam to a smaller point. But when we're already dealing with a beam that isn't focused to a point, I don't see why that would make any difference. I'm sure I'm missing something, I just don't know what!

=====Why I care=====
I care because I'm working on an invention that needs a very bright light source with a similar divergence and waist with as a consumer projector, but that needs to be a very narrow wavelength. Because of the narrow wavelength requirement, I've opted for a laser. I've done experiments with something like a laser genetics ND3, which works well, but isn't bright enough, and my concern is that if I go much brighter, it will exceed the limit for a 2m laser (which is not an option - the invention will be a consumer device). The ND3 is a 2m laser with a 40mw diode. Assuming that a 532nm diode creates ~600 lumens per watt, that equates to about 24 lumens, which isn't much. On the other hand, a laser projector (which as I understand it uses a diffuser to make the laser light incoherent) can be 10,000 lumens and still be in risk group 2, which approximately equates to class 2m for lasers (i.e. there's no risk of eye damage due to aversion responses). The ND3 has a similar size lens that the light escapes from as a projector, and a similar divergence. If you put your eye right up to the projector, or the ND3, it seems to me there wouldn't be much difference in terms of the % of the total beam entering your eye, and the divergence of that beam - only the projector is 10,000 lumens, and the ND3 is 24. Does that mean I could have a 10,000 lumen version of the ND3 and it still be class 2m?

Obviously if I opted for a more traditional light source, then I'd have to filter it down to a narrow wavelength, and throw most of the light away - but if I did this instead, would it be safer than the laser version? If so, why?

Finally, if there is some reason why laser light is inherently more dangerous than the same flux level of 'normal' light, is there some way to remove this without altering the wavelength?

Sorry about all the questions, and thanks - I'm a real beginner so any help would be amazing!
Light is light no matter the source. Any source if light can be dangerous. The thing that makes laser light dangerous is it starts from a very small area, small enough to be considered a point source dumping a lot of energy into a point on a retina when focused by the eye's lens.
 

Cyparagon

Well-known member
Joined
Sep 12, 2007
Messages
9,823
Points
113
Any source if light can be dangerous.


 

CurtisOliver

Well-known member
LPF Site Supporter
Joined
Jun 12, 2015
Messages
6,887
Points
113
Well Steve isn't exactly wrong with that statement you quoted. The only nit-pick is that he should of made clear about the power aspect.
'Any source of light can be dangerous if given enough energy'. Rather than just belittle using a gif why don't you tell us why this is a false statement to make. Give anything enough energy and it becomes dangerous. Lasers are incredibly dangerous due to the power density they can deliver and coherency just means that a large proportion of the photons are travelling in the same direction. A torch or projector light will not reach the same levels of power density nor is coherent, but I still won't see myself looking into the source of the light.
 

RedCowboy

Well-known member
Joined
Jul 10, 2015
Messages
9,690
Points
113
I have played with LED's that emit narrow enough that you can see the interference pattern, why not a LED or an array of LED's ?
What wavelength are you looking for ?

 

adam1128

New member
Joined
Jun 1, 2018
Messages
8
Points
1
So I appreciate the input, but I'm still no closer to hearing a properly argued answer to this. I entirely understand that power density is a key factor, but I'm asking, assuming the power density is the same, is a laser any more dangerous than a lamp?

The most sensible thing I have read is that coherent light is much more easily focused by the eye itself, so that if two beams of light hit the eye, both with the same power density, but one coherent and one incoherent - then the coherent beam will be focused by the eye to a much smaller spot on the retina, hence meaning that spot will have a much higher power density, and so do serious damage. Whereas the incoherent beam won't be focused to such a small spot, and so the power density won't ever get that high.

Which implies that for my invention, getting a very powerful incoherent source and then filtering it down to a super narrow bandwidth would be much safer than getting a coherent source (i.e. laser) at the same wavelength and power density.
 

jors

Member
Joined
May 9, 2014
Messages
79
Points
18
Its about size of emitting point as well, Laser diodes have a very very small emitting point. Without taking other considerations (coherent etc) this is also the reason spot will be smaller when focused than with other light sources. You can't get so small emitter with that huge amount of photons with 'current' light sources (yes, energy density), even with pumped phosphors (non-coherent) is not possible.
 

Alaskan

Well-known member
LPF Site Supporter
Joined
Jan 29, 2014
Messages
12,646
Points
113
Simple reason; High Power Density is possible from tiny emitters when focused to a tiny spot.

You didn't ask, but the reason the output from a laser diode without a lens (uncollimated) is more dangerous than incoherent light is due to the size of the emitter being so small the lens in your eye can focus the energy down to a very small high power density point and burn the back of your eye in a flash.

As far as whether the light entering the eye is coherent, or incoherent, a large enough amount of incoherent light can burn more than a smaller amount of coherent light, of course. Depends upon the amount of power, also much depends upon focus variables too, so keep that in mind.
 
Last edited:

adam1128

New member
Joined
Jun 1, 2018
Messages
8
Points
1
I have played with LED's that emit narrow enough that you can see the interference pattern, why not a LED or an array of LED's ?
What wavelength are you looking for ?


Thanks - that's a good idea. I've looked previously but never found anything that was narrow enough. Do you have any other examples? I couldn't see a spectrum for the Ebay example you gave (I might have been looking in the wrong place).
 




Top