Probably a Simple Physics Question - Settle Our Argument

So to confirm:

I understand that physically there is twice as much light... but would it be twice as bright?

The answer is: Yes, although to the human eye it wouldn't be so extreme.

Correct?
 
Brightness would be a factor of the light being reflected from the surface. So if everything was ideal (i.e. perfect reflector) then yes, it would be twice and bright.

Also you then need to think about where you stand and light scattering.
 
Simplest way to think of it:

Light intensity is measured by the number of photons per area. So two lights are definitely twice as bright as one! The reason it won't appear twice as bright is mostly to do with your eyes. Your pupils control how many photons enter your eye depending on how bright whatever you are looking at is. So twice as many photons bouncing off the object you look at will not translate to twice as many photons hitting your retina.
 
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taximike said:
Simplest way to think of it:

Light intensity is measured by the number of photons per area. So two lights are definitely twice as bright as one! The reason it won't appear twice as bright is mostly to do with your eyes. Your pupils control how many photons enter your eye depending on how bright whatever you are looking at is. So twice as many photons bouncing off the object you look at will not translate to twice as many photons hitting your retina.
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The iris does immediate adjustment of the amount of light entering the eye, but most of the adjustment is slower and is due to a series of proteins in you retina adjusting the sensitivity of the light-sensing cells (rods and cones) in your retina to adjust the dynamic range of your vision. Otherwise your eyes would need to be able to accurately discriminate light intensity over many orders of magnitude. This is also why everything is so bright and overexposed after walking into sunlight after being inside in a dark room, and your vision then normalises.Wiki
 
eLbot said:
Entertaining the idea of light as a wave (that'll upset physicists but its useful to explain here) and that there is phase coherence wave interference can occur. If the second light were to superpose with the first light source it can disrupt the propagation of the first reducing the amplitude. The first can also do the same to the second, reducing the amplitude of the second. This results in the final result of an overall increase in intensity at the point of observation but not a doubling effect.
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But then entertaining the idea of light as a particle, double the number of lights and you double the number of photons landing on the surface :p

I don't think there is a simple answer :p

However, the diffraction grating relies on the light being a steady wavelength I think I remember. It's not white light which is a spread of all wavelengths. In the case of white light there will be construction, destruction and interference. My brain hurts.

I bet it's a root mean square law :D

2 lights = 1.4 times the intensity approx :)
 
JCBeastie said:
Coming from a guy that seems to believe additional light sources somehow cancel each other out, contrary to observable and theoretical results.
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This is not what I previously thought.

I'm surprised you react to sarcasm, though. Seems mildly hypocritical.

Thanks to everyone else though, who have understood that when I opened the thread with "I dont understand", that I was in fact implying that very thing, and thus haven't resorted to the "lol ur idiot" approach.
 
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DampCat said:
This is not what I previously thought.

I'm surprised you react to sarcasm, though. Seems mildly hypocritical.

Thanks to everyone else though, who have understood that when I opened the thread with "I dont understand", that I was in fact implying that very thing, and thus haven't resorted to the "lol ur idiot" approach.
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Actually you started a thread debunking the concept, and went on to accuse your colleague of "using vague and confusing examples" when you failed to provide anything more concrete yourself; I found the situation to be ironic.

You went on to use an example using sound, to convey your limited understanding of how light functions; a muddled and unfair comparison.

While you are probable correct in saying it doesn't 'double' but you can certainly increase the intensity, you also brought in the concept of 'spread' when also assuming that the area was completely and presumably evenly lit.

I certainly wasn't calling you an 'idiot' but I felt you were being hipocritical, that is all.
 
Meridian said:
when you add the second speaker you do double the sound energy, but since the human ear hears on a logarithmic scale it only sounds a little louder. Much the same happens with light as the human eye is so good at adjusting fro brightness: the light level will be twice as high, but you won't think of it as such.
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... The correct answer.

But since human perception is subjective, doubling of the light energy (or equivalently, doubling of the photon count, since each torch gives off light with the same intensity distribution) is the only truly valid universal measure. The "brightness" doubles.
 
Nice twice as bright, it would be percieved by our eyes as a bit brighter.

Both human eyes and ears are logarithmic...

EDIT: Meridian worded it much better than me. :)
 
DampCat said:
Surely an identical beam of light will just merge with the first with no observable result? :(

If I was doubling the power output of the first light, it'd be twice as bright, but a separate identical light isn't producing twice the power, its producing the same power... isnt it?
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It is producing the same power indeed, but this power is being projected onto some surface (in this example, a wall). The wall now has two identical beams focused on it. Energy doesn't disappear :)
 
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