All of you seem to have forgotten absorption differences between wavelengths.
Example:
300mW of 808 cannot punch through a piece of white paper at all.
300mW of 445 will cause the paper to begin smouldering within seconds.
Another example:
150mW of 780 cannot light a white-tipped match
120mW of 405 can do it within seconds
And yet another:
I cannot feel a 500mW 808nm beam on my skin
A 500mW 445nm beam immediately causes a stinging sensation to be felt where it hit.
Think about it. If you get hit in the eyes, you're screwed either way.
But if you miss the eyes?
Oh, and don't forget the Blue Light Occular Hazard associated with 445nm. Such a thing doesn't exist for IR.
Taking into account albedo of a given surface, it really depends on power density, like piferal was saying.
For your example of 808nm and 780nm vs. 405nm, I would have to disagree.
I can easily feel the warmth from a 4mm x 4mm beam of 808nm at 500mW on my skin (I am fairly tan but not dark). When focused to ~1mm x 1mm, it absolutely burns. Yes, organic materials tend to reflect or pass IR more than light on the other end of the spectrum but the difference is not so great as it seems.
Regarding the "blue light hazard" issue - it is true that there is more variety of health risks associated with short wavelengths but the way I see it, it does not make blue light "more dangerous" than any other light. It is just as dangerous but in different ways.
Because using a 1W 445nm laser puts you at risk of bleaching the pigment in your photo-receptors does not make using a 1W 808nm laser in the same environment any less hazardous to your eyesight (or skin for that matter). I know first hand, as you might, that 1W of power, if concentrated, whether it be 445nm or 808nm, has no problem quickly decomposing whatever the beam falls on.
Of course, as others have pointed out, lasers do not have to be "dangerous" by necessity. It is more the "misuse" of them that makes them dangerous rather than the beam of light itself. Again, how "dangerous" something is can't be quantified. The amount of energy in a beam of light
can.
So the
subjective answer to "what color is more dangerous?" is ambiguous. However, we can
objectively determine what the risks are associated with wavelength x or wavelength y, which ultimately depends on the amount of energy your eyes or skin or clothing is exposed to and not necessarily the properties of the light.
To make this clear: Would you say that a 1mW 445nm laser is more dangerous than a 1mW 650nm laser?
If the 445nm wavelength is inherently "more dangerous" than 650nm, then you would say yes. However, that is not the case, because it is simply visible light at a non-ionizing wavelength just like 650nm. Is there a significant risk of photochemical damage with 1mW of 445nm? No. Is there a significant risk with 1000mW? Absolutely. Is there not also a significant risk of eye injury with prolonged exposure to 1000mW of 650nm laser light? There absolutely is. So what this means to me is that it is not necessarily the wavelength of the light that we should be concerned with but the power level.
If 445nm or 405nm light is more dangerous than any other light in the visible or infrared spectrum, then why don't we go outside with laser shades on or a blue light-proof jumpsuit to protect us from these wavelengths?
Because it is not the wavelength itself that harms us but the amount of the light that we are exposed to.
Why does everyone keep saying that? To me, the definition of danger to a PERSON is skin and eyes. Danger to different colors of paper, plastics, wood, etc. just sounds stupid.
And he did specify handhelds that he was wondering about, which everyone seems to neglect to see (it's on the first page, his 2nd post)
I agree with you that the albedo of paper or plastic is irrelevant unless we are speaking in terms of fire hazards. But then again, there is my point... we must first define a specific circumstance that defines "danger" and even then, it depends on the power and the power density. You can't light a fire with a 5mW laser beam, can you? How about a 405nm laser 500mW with 10mm beam diameter? Not likely.
Going back to the radiant power of the Sun... (The surface of) Earth receives more energy from the Sun in one minute than all our dinky little laser pointers output in a lifetime (and in every wavelength from ~380nm to far into the infrared). So why is it that we can walk down to the beach on a sunny day or inhabit the planet at all? Because the energy is distributed over a huge surface area.
Another example: the force that drives a bullet out of a barrel and to its target at incredible speeds. If you ignite the propellant in a large volume container, the result would be less than spectacular. However, releasing that energy in a tiny volume creates high pressure that forces the projectile to travel in one direction at high speed. So it is then not the amount of propellant itself that determines how fast the projectile will travel but also the volume that the energy occupies.
Also, whether the beam is coming out of a hand-held laser or out of a unicorn's ass, it really doesn't matter because coherent light will behave like coherent light regardless of whether you can twirl the laser like a lightsaber or not.
(Not trying to be rude - just thought it was an interesting comparison
)
