Re: is a 10mW greean laser twice as bright as a 5m
Well, short answer, I would assume that if you had a 10 and a 5 milliwatt laser side by side, you will notice the differeenc, but not be impressed by the difference. I have seen this with other lights, but not lasers.
-Bill
Long boring answer alert! Please feel free to skip when your eyes start to glaze over /ubbthreads/images/graemlins/wink.gif
Technically, humans perceive light and sound in a logarithmic nature, not linear.
Power is equal to P=V^2/R or = I^2*R or = I*V
Power can be represented in decibels and is equal to 10*log(base 10) of P (of above). There are other things that play into the equation and different reference limits (i.e., referenced at a milliwatt) so that you don't have to deal with negative numbers. Use 20*log of direct voltage or current measurements (notice that power is proportional to the square of the voltage or current or amplitude--hence bring of the factor of two to the front of the equations). All of this is from years ago--so please feel free to correct if I messed something up.
So, if you double the voltage (or current) to an emitter (and all other things being equal, and you have a "linear" emitter) then you get 4x the power.
If you add a speaker in parallel (or even in series) with another speaker to the same amplifier tap, it really depends on the output characteristics of the system (does the amplifier distort because of a miss-matched load, increase output current, the dynamics of the speakers, etc.). (I am not an audio engineer--just a technical observation).
If you add a second amplifier and speaker, same power and in phase, you will only double the power (i.e., 10 watts plus 10 watts = 20 watts).
From my casual experimentation with sound, I typically found that a doubling of power (3 db or sq root of 2 -- or 1.414 times voltage (or current) increase) is barely noticeable and you would typically need an A/B comparison to confirm the difference.
If I double the power (6 db or 2x the voltage) the effect is very noticeable and is probably something that you would notice without an A/B comparison.
An increase of 10x power and (10 db or ~3.16x the voltage) and the higher output completely swamps the effect of the lower output.
Anyway, you can experiment yourself with a stereo and a voltmeter or an LED and a ammeter (or a light meter). I suggest the LED because its output seems to be much more proportional to input power. An incandescent light is not linear at all.
As another example, if I recall correctly, the ARC4 adjustible output light uses db steps, not linear steps, to create the visual effect of even steps between minium and maximum output levels.
As always, your mileage may vary...
-Bill