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# mW or nm  - Which factor counts most for burn

#### RWTroll

##### New member
As most of you know, I am still new to these light sabers, lol

I have a newbie question, it seems mW is noted mostly in power, but what are the factors of nm, I guess this is the wavelength or spectrum of the light ?

What would be more powerful for burning, a do it yourself red at 150mW, 539 nm
or a 400mW > 808nm

I know this question is rather strange, but I am in the process of purchasing a 400+ mw 808nm, but was told the actual power output of them is really like most 150 mw lasers with a lower nm - because 808nm is almost all IR wavelength and thus less power for burning. I mean I have watched pseudos videos of the 400 mw burn and Kenoms reds with a lot less mw seem to be burning as good ! Can someome explain.........

#### RobTheVIP

##### New member
Re: mW or nm  - Which factor counts most for

1 mW = 1 mW

The wavelength does not change the power, it only changes the visibility.

#### RWTroll

##### New member
Re: mW or nm  - Which factor counts most for

Wow! It can't be any simpler than that..... lol thanks 'RobTheVIP'

#### nes_ds

##### New member
Re: mW or nm  - Which factor counts most for

RobTheVIP said:
1 mW = 1 mW

The wavelength does not change the power, it only changes the visibility.
To add to ROB's post, there is one thing else that wavelength differs, and that's how small the dot can be focused, it doesn't matter much for visible lasers. It's pretty simple to understand, 532nm can be focused to a 522nm(nano-meter), once it reaches a beam diameter of 532nm, if begins to spread out again, or diverge. This is why Blu-ray(405nm) disk can hold much more then DVD's(650nm).

#### pseudonomen137

##### New member
Re: mW or nm  - Which factor counts most for burn

THe other factor is that different things absorb power differently. mW is absolute - it tells you how much power there is in the beam regardless of the nm. However, most black rubber is very good at absorbing 808nm, whereas red items are likely to absorb little 808nm, meaning they will not burn well. Just like its easier to pop a red or black balloon with a green laser than a green balloon.

For some reason though, the misconception that mWs of 808nm are less powerful than mWs of 532nm is rampant on places like YouTube. Since its a widespread belief on youtube, we know its wrong.

#### ixfd64

##### New member
Re: mW or nm  - Which factor counts most for burn

When I was young, I used to think that lasers with smaller wavelengths burned better.

#### benthegeek

##### New member
Re: mW or nm  - Which factor counts most for

Shorter wavelengths have more photon energy, so a certain number of blue photons will be more powerfull than the same number of red photons. In reality though, this difference is quite small when you tap it on the end of a bazillion photons that are emitted from any laser each second. Power becomes the ultimate factor.

You can do the math.

Photon Energy (Jouls)= Plancks Constant (Joul Seconds) x Frequency (Hertz)

Frequency (Hertz) = Speed of Light (Meters per Second) / Wavelength (Meters)

Power (Watts) = Total Energy (Jouls) / Time (Seconds)

Now, put Photon Energy into Total Energy, knowing that:

Total Energy = Number * Photon Energy

Where Number is the number of photons that are emitted in the Time so

Power (Watts) = [Number x Plancks Constant (Joul Seconds) x Frequency (Hertz)] / Time (Seconds)

Putting in the second equation,

Power (Watts) = [Number x Plancks Constant (Joul Seconds) x Speed of Light (Meters per Second)] / [Time (Seconds) x Wavelength(Meters)]

For the same power, you need less photons (Number) to make up for the decrease in Wavelength

I'de elaborate more, with a graph, but I have to attend a advanced screening of Kingdom. Movies trump math