mW = milliwatts. Which measures the power outputted from your laser, just like a light bulb in your house, however a light outputs INCOHERENT light (irradiating in all angles, so the light fills up your whole room.) While, on the other hand, a laser emits coherent light, where all the photons are emitted in a straight, beautiful, laser beam! I guess you would call this strength.
Now, NM (nanometers) is the measure of the wavelength of the light emitted. A light bulb in your house releases white light, which as you know is a combination of all other visible wavelengths. The typical green laser emits light at ~532nm, which your eye interprets as green. Your eye can sense light roughly between 380 and 750nm, however green is in the middle and seems brighter because your eyes are most sensitive to it.
Now because your eye is most sensitive to 532nm light, a 5mW green laser will "seem" much more brighter than a 5mW red or purple laser. Both lasers are equally "strong" as they are outputting the same amount of energy, however the green is "brighter" to your eye.
It is said that the human eye "brightness peak" is actually at 555nm.532nm is as close as a hobbyist can get to it, so the brightest laser you can get is 532nm.
And it is true that brightness depends on your eyes and is not proportional to power.It's a (non-linear) function of power and wavelength.
Also be aware of the correct SI prefixes and units: uppercase A, V, W for amps, volts and watts ; lowercase m for meters and also for the "mili" prefix ; uppercase M prefix is for "mega", and uppercase N is for newtons. :
mW determines it's brightness and how much light it's putting out.
nm determines it's color......[/quote]
I think it might be good to know that outside the visible spectrum...mw also means cutting power...not sure if nm has anything do with it. cutting lasers has always been a mystery to me. I've see it cut sheet metal, but very little has been told me about it