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# Laser burning power cleared up.

#### Kenom

##### Well-known member
Ok, I donno how many times I've fielded the question "which burns better Green, bluray, or red?" As such, I'd like to take some time to clear up this issue once and for all (if this becomes a sticky)

First off there are a few factors to consider. I don't have a degree in Physics so can't go in-depth explaining the whole reasons behind what's what. I do however know what does affect burning power and can go into the general different factors determining burning power of a laser and what your burning.

First off lets clear up the mW issue. Like comparing quarters to dimes, you go with the basic break down of the individual group you are utilizing. I.E. Pennies. You describe to someone who has no concept of a quarter or dime and you have to first explain what a penny is. The penny is the lowest form of currency in the United States. As such, you use it for determining value of all other monitary denomonations. A quarter is the same thing as 25 pennies. A Dime is the same as 10 Pennies. Same with mW. miliWatts = 1/1000 Watt. Now there are lower denominations of laser power but in a hobbyists book it is the baseline. So, given that a mW is the same as a penny, you can see that comparing one penny to another penny is a waste of time. They are the same thing. A mW when compared to a mW is the same thing regardless of wavelength of the laser. This is only a expression of energy. The energy of a 1mW green laser is the same as the energy of a 1mW red laser.

Second thing to consider. What are you burning? This is important primarily because different materials and different colors react differentlly when exposed to different wavelengths. This is where my specific lack of knowledge in physics has to be filled in by somone else more knowledgable than I, but I do know that something like a flourescent rock, cannot be burned by a 405nm laser because of the flourescent reaction in the rock unless there is a massive amount of energy. This mostly has to do with dispersion of energy from my understanding. The energy is being changed to something else so does not have the effect your looking for. On the other hand, black electrical tape, which absorbs a lot of different wavelengths, can be easily burned by many numerous lasers. I'm really going to rely on others here to explain a bit more in-depth as the the hows and whys of this. Basically it comes down to one thing. Beam absorption. If the beam gets absorbed, it can be burned. However, if the beam DOES NOT get absorbed, then your going to need a vast amount of energy in order to burn it. White reflects green very well. In order to burn white, you have to have a lot of energy. Now this is not only color dependant. There are many different things to take into account for it, but essentially it boils down to what you want to burn.

Bluray burns white paper very well. However not all white paper will burn when exposed to bluray. It truly depends on the material.

Green hates red. I read somewhere they have a tendency to cancel each other out. Shine a green light on a red apple and that apple appears black. I know there's more to it than just a red apple only reflects red so when green is shone on it there's no light. but am lackin in the particulars when it comes to lasers.

So, while the effect was to try to illuminate the whole subject and settle it once and for all, I'm sure I've just confused everyone and will allow the knowledgable folks out there with the physics degrees to pop in and give the technical explanations need to educate even me.

#### Cyparagon

##### Well-known member
Kenom said:
Basically it comes down to one thing. Beam absorption.
Beam diameter also plays a large role. 405 has a smaller focal point than 660, and 660 has a smaller focal point than 532.

#### MarioMaster

##### Well-known member
Cyparagon said:
[quote author=Kenom link=1238729215/0#0 date=1238729215]Basically it comes down to one thing.  Beam absorption.
Beam diameter also plays a large role. 405 has a smaller focal point than 660, and 660 has a smaller focal point than 532.[/quote]

don't you mean 532 has a smaller focal point than 660?

#### Cyparagon

##### Well-known member
You'd think so, but 532 has a smaller initial beam diameter generally 1mm where 660 generally has 4-5mm. You'd need to expand the beam of a green, then focus it to achieve a smaller focal point. Someone generally doesn't go to all that trouble to light a match

#### bobobob121

##### New member
ooo lucky me = D i did my science fair project on this and its decided that blu-ray burns better than red because its closer to the UV light on the color spectrum like that coming in the suns rays which can give you a sun burn

of course i did numerous test from different distances with very similar mW and beam diameter lasers.

#### Kenom

##### Well-known member
Well this topic needs to be stickied so that everyone who asks that question can be referred back to this thread.

#### Cyparagon

##### Well-known member
Yes, we certainly need more stickies! 46 more at LEAST

#### styropyro

##### Well-known member
Cyparagon said:
Yes, we certainly need more stickies! 46 more at LEAST
There are a lot of stickies in this section, but as discussed in this thread we are trying to clean up the wall of stickies with "Threads of Interest" topics to save a bunch of space. This would be a good thread to add to that list.

#### 691175002

##### New member
bobobob121 said:
ooo lucky me = D i did my science fair project on this and its decided that blu-ray burns better than red because its closer to the UV light on the color spectrum like that coming in the suns rays which can give you a sun burn

of course i did numerous test from different distances with very similar mW and beam diameter lasers.
That is incorrect, by your logic the shorter the wavelength the better it burns which is absolutely untrue, CO2 lasers which are used for cutting metal etc fall very far into the infrared spectrum.  As a matter of fact, anything in the visible spectrum would be useless for cutting metal since it would act like a mirror and reflect instead of getting absorbed and heating.

The reason why UV light gives sunburns is because each individual photon has enough energy to destroy DNA which causes cancer etc. If you wanted to burn a hole through someone UV would not be significantly any better than any other wavelength (Aside from perhaps red).

There is nothing hard about laser burning power, the more of the laser that is absorbed the more of the laser gets turned into heat to burn.

Basically this means that any light you can see is light that is not heating the material. (And is instead being reflected into your eyes)  A laser will appear brighter on a white sheet of paper than a black sheet of paper which is why black burns more easilly.  A red laser will burn all colors of paper that do not reflect red (Get a color wheel or look up subtractive color theory).  Ditto for every other color.

I would make a list of what colors absorb what wavelengths, but this is really basic stuff.

And don't even start about certain wavelengths focusing better than others.  I'd like to see someone try to focus a laser by eye to the diffraction limit.

#### meatballofall

##### New member
I agree with this dude above this post. Material, color, energy absorbed, etc. But in reference to kenoms first post, a mW is a unit of power, yes? The ability to do work? If that's the case, then out of two differing wavelength lasers being run at say, 5mW, would it not be the laser with the smaller (higher energy) wavelength that has the ability to do more "work".? Isn't it kind of like trying to compare radio waves to x-rays? You need dozens of watts to drive an FM station, but only a few watts of x rays to ionize and destroy cell tissue?

#### Kenom

##### Well-known member
it's not based on work because work is relative. your changing it from energy to "work" it's not the same correlation.

#### chipdouglas

##### Well-known member
In my opinion people who need this thread probably only care about the stuff they can burn with their lower powered diy's or whatever. So that said, I'm sure people on here won't mind sharing their burning experiences, Ex. what they burned with what laser and set to what power..

thanks
michael.

#### alf638

##### New member
Also the shorter the wavelength of the laser the better it will burn as shorter wavelengths are able to interact with smaller molecules/atoms. It also means it will be able to burn a wider range of things.

#### ped

##### Well-known member
Alf638

Can you please stop posting in 18 month old threads, its frowend upon and you WILL be banned.

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