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Old 03-05-2009, 02:20 AM #1
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Default Danger from IR leakage from lasers vs IR heaters

I am not an expert on lasers,so I can't help but wonder why IR leakage from a laser is dangerous but IR radiation of 1600 watts or even 3000 watts from common IR heaters that we use in our homes is no danger to our eyes at all ? What is the scientific explanation for this ? Not that I am denying the danger to the eye from lasers without IR filters or anything...


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Old 03-05-2009, 03:07 AM #2
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Default Re: Danger from IR leakage from lasers vs IR heate

IR from heaters is not focused laser light and at a broad band spectrum.

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Old 03-05-2009, 08:07 AM #3
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Default Re: Danger from IR leakage from lasers vs IR heate

If "focus" is the criteria, then the visible beam (red, green or whatever) emitted by the laser is already quite dangerous isn't it? Why is there an emphasis on an IR filter ?
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Old 03-05-2009, 09:09 AM #4
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Default Re: Danger from IR leakage from lasers vs IR heate

GOOD QUESTION!!

The argument goes: you can't see IR and therefore IF something were to separate the IR from the green, there's a SLIGHT chance you could be exposed to a LOW power density IR beam without knowing it.
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Old 03-05-2009, 01:58 PM #5
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Default Re: Danger from IR leakage from lasers vs IR heate

The primary issue with IR leakage and IR laser exposure in general is that your blink reflex is useless. You eyes don't know to close and your head to turn away during a potential dangerous exposure. This allows your eyes to generally be exposed much longer than to an equivalent exposure of visible laser light.

Exposure to a heating coil (IR radiator) versus an IR laser are two different beasts. A heating coil radiates at a wide range of wavelengths from visible (if hot enough) out to far IR in a non-coherent fashion. Read up on black body radiators for a good background in radiators and color temperatures. An IR laser on the other hand is not only monochromatic but also coherent. Every photon is in perfect phase with every other photon. All the wave functions are peaking together providing a much more intense exposure mW for mW when compared to any other natural light. Read up on bosons for a good understanding of how every photon can occupy the same quantum state as well as an understanding of how stimulated emission occurs.
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Old 03-05-2009, 02:20 PM #6
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Default Re: Danger from IR leakage from lasers vs IR heate

Thanks for the infornation. It's hard to imagine that a laser of say 100mW can be more dangerous than an IR radiator of 1000 Watts.....the difference is in the order of 1E6 x 1E3 x 1E-2= 1E7.....10 millions times more power.....yet it's the smaller one that's dangerous....

Maybe another scientific explanation would be as follows : Energy delivered in seconds (watts) per AREA (m2 or inch2 for those of you in the US) of a laser beam could turn out to be significantly larger than that for an IR radiator because beam from an IR radiator is not focused i.e. 1000 watt is delivered to a wider range of area and the portion of that beam that hits the eye is smaller compared to a direct hit from a laser.
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Old 03-05-2009, 06:14 PM #7
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Default Re: Danger from IR leakage from lasers vs IR heate

Hi,

I tried to visualize a bit whats the difference between a ligh bulb and a laser. No photons involved, just geometry .
Its the fact that a laser emits all its radiation in one direction that makes it so dangerous.
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Old 03-05-2009, 08:07 PM #8
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Default Re: Danger from IR leakage from lasers vs IR heate

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Originally Posted by andythemechanic
Hi,

I tried to visualize a bit whats the difference between a ligh bulb and a laser. No photons involved, just geometry * .
Its the fact that a laser emits all its radiation in one direction that makes it so dangerous.
That's a really good way of illustrating it... Another thing to note is that heat is something like 10,000nm and the cornea is opaque to such low wavelengths.
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Old 03-05-2009, 08:24 PM #9
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Default Re: Danger from IR leakage from lasers vs IR heate

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Originally Posted by pseudolobster
[quote author=andythemechanic link=1236223215/0#6 date=1236280469]Hi,

That's a really good way of illustrating it... Another thing to note is that heat is something like 10,000nm and the cornea is opaque to such low wavelengths.
Depends on Temperature. The physics here is Wien's displacement law, see http://en.wikipedia.org/wiki/Wien%27s_displacement_law
10,000 nm is, when I remember correctly, roughly equal to 30C. A hot barbecue fire has its maximum emmission already at 2000nm .
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Old 03-05-2009, 09:45 PM #10
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Default Re: Danger from IR leakage from lasers vs IR heate

Good image. However, the bulb appears to be focused to a point which isn't the case. If you try focussing the light of a bulb, all you get is a smaller image of the bulb.

The beam of a laser on the other hand represents to the eye something that is very far away - the light beams emitted from an object far away are virtually parallel like that of a laser. Objects that are very far away appear small because the light is focused to a small area on the retina.
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Old 03-06-2009, 03:48 PM #11
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Default Re: Danger from IR leakage from lasers vs IR heate

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Originally Posted by Cyparagon
Good image. However, the bulb appears to be focused to a point which isn't the case. If you try focussing the light of a bulb, all you get is a smaller image of the bulb.

The beam of a laser on the other hand represents to the eye something that is very far away - the light beams emitted from an object far away are virtually parallel like that of a laser. Objects that are very far away appear small because the light is focused to a small area on the retina.
You're right it's a bit simplified. It takes not into account spatial coherence of the different sources but only is a geometrical model, assuming a point-like light bulb. It catches only the fact that from the laser more Energy hits the eye and tells nothing about, how good this light can be focused onto the retina. When you take this into account the image of the light bulb will appear on the retina spreading the energy over some space while the laser will focus to a tiny spot making energy density on the retina very high.
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Old 03-08-2009, 07:07 AM #12
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Default Re: Danger from IR leakage from lasers vs IR heate

Ir leakage from a green pointer isn't dangerous at all compared to the green that is coming out. Worry about the green.

an IR LASER on the other hand, is very dangerous. All that infrared will be focused in a beam coming out and you will have no blink reflex.

Also, most DPSS lasers (yag, 808nm diode, etc) emit near IR. This is light that is invisible to the eye, yet still passes all the 'mechanics' of the eye and makes it to the retina, where it can cause damage. IR from one of those heaters is mostly mid and far IR. When the wavelength becomes long enough, IR light ceases to pass the cornea. This is why you will feel the heat on your eyes, because even though they are 'clear' to visisble light, they might as well be black to this far IR light.

It's the same reason a CO2 laser (10,600nm or 10.6um) will never damage your retina, but it will toast the surface of your eyes.

Also there is the whole coherent vs. non-coherent thing that has already been explained in this post.
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