is a 10mW greean laser twice as bright as a 5mW?

Shredhead

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is a 10mW greean laser twice as bright as a 5mW? then would a 25mW be 5 times brighter than a 5mW...just a little confused /ubbthreads/images/graemlins/whoopin.gif
 

BB

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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
 

Shredhead

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Re: is a 10mW greean laser twice as bright as a 5m

ok...what about comparing a 5mW to 25mW? is there a noticable difference there? /ubbthreads/images/graemlins/wink2.gif
 

BB

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Re: is a 10mW greean laser twice as bright as a 5m

Yes, 5x falls in-between the 2x (noticeable) and the 10x (blown away) examples of above.

But, as always, remember there is a reason for the 5mW limit--it is to help prevent loss of vision of a laser pointed into the eyes or off a reflective surface. A good solid 5mW green laser is still much much brighter appearing that the standard 1-5mW red lasers you see around everywhere.

I guess the real question is what is your use. I am sure that there are plenty of folks here that can recommend a power level for your needs. Having one that is too bright for the application (or the user) is just plain risky and not recommended (an is, in fact, illegal and can open the owner to liability if somebody is injured).

-Bill
 

Shredhead

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Re: is a 10mW greean laser twice as bright as a 5m

"Yes, 5x falls in-between the 2x (noticeable) and the 10x (blown away) examples of above."
uh..what in heck does that mean??? /ubbthreads/images/graemlins/party.gif
 

BB

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Re: is a 10mW greean laser twice as bright as a 5m

I was just saying, that 25mW/5mW = 5x more power. 2x is something that you may notice (i.e., my ARC AAA flashlight may need new batteries) and 10x (my ARC AAA beam is swallowed up by an Surefire E1 or something).

Sorry, I guess I am not explaining things too well. Our eyes (and ears) are non-linear. We really see and hear in a logarithmic scale--or more to the point, we see things as fractions (ratios) instead of linear addition. I.e., 25mW/5mW=5x more power. Instead of 25mW-5mW=20x "bigger or brighter".

And in the big scheme of things, a fractional difference of the sq rt of 2 (1.414) is only noticeable in an A/B comparison--two side by side at the same time (a 1mW vs a 1.4mW). Something that you can tell the difference of one day to the next is a fractional difference of 2 (i.e. 1mW vs 2mW or 25mW vs 50mW). And something that is 10x bigger is a big difference (1mW vs 10 mW, 25mW vs 250mW, etc.).

We can hear and see in something like a 130-145 db range--that is the equivalent of a tape measure marked in 1/16" units that can extend out to almost 312 million miles (i.e., accurately measure from 1/16" to 312,000,000 miles).

Here is a guy that tried to quantify these big differences with respect to light levels in engineering terms:

What's all this optical stuff, anyhow?

In any case, I recommend that you give the application that you need the laser and ask what power is sufficient (i.e., indoor presentation, outdoor in bright shade, at night pointing out stars, etc. A 25mW or 50mW laser is dangerous--it can permanently blind somebody. That is why there are laws and regulations regarding their use (but not their possession).

-Bill
 
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