Two 30w Lights - Same Intensity As One 60w?

Having a brain fade at the moment.

If you had two 30w lights lit next to each other, would the overall light intensity given off by them and measured at a set distance be the same as one 60w bulb?

I.e. if you lit a room with two 30w bulbs in a lamp would you notice any difference if they were swapped for one 60w ?

Similarily, if a point in a room was lit by a 30w light and you then added another 30w somewhere in the room, then another, and another. Would that point get progressively brighter and brighter?

Hi!
Sure, two light bulbs or more add their powers if they are next to another.
[Just for QM fanatics: they add power and not wave amplitude because their light isn't correlated. Sorry for the interruption.]

But what is better, you can put your light bulbs wider apart, avoiding the disturbing shadows that a single one would create. The benefit is similar to indirect lighting, and you don't waste 2/3 of the power heating the ceiling.

Light output is measured in lumens with the lumens adding by adding more bulbs. The only difference is how the light will be distrubuted if it is separated into two sources. If the two bulbs are close it would look similar. If the two bulbs were separated into opposite sides of the room, you would get a different look in the room. Each source would look less bright close up, but the opposite side of the room would become more illuminated. The middle point in room-space would have the same light intensity in both cases. Solid objects in the middle would look dimmer on one side, but would look brighter on the opposite side where a shadow one was.

Thanks for that.

Is the same also true for sound and other waves and forms of radiation?

To clarify: visible light output is measured in lumens, but a 30 watt bulb won't necessarily put out half the lumens of a 60 watt bulb. Watts are a measure of power consumption, more efficient bulbs will put out more lumens per watt.

Other forms of radiation do in general add, though again, actual power output isn't the power consumed. A 100 watt speaker system won't put out 100 watts of sound, it'll put out 100 watts of sound + waste heat + vibration dissipated into solid structure rather than the air + stray electromagnetic radiation + whatever else might contribute to the losses. Also, depending on the situation, you won't necessarily get smooth mixing...you can get an interference pattern with high peaks where the sources reinforce and dead areas where the sources cancel out. Overall, the sources add together, though.

Also, perception can do funny things, especially with sound and light. Two light sources will give softer, lighter shadows, due to each filling in the shadows of the other. The greater effectiveness in getting light into shadowed areas may make them appear brighter, or the loss in contrast may make them appear dimmer. And then there's the way the eye and ear can adapt to different light/sound levels...

Yes, subjective impression can be very different from a measurement.

Sound and other waves:
- As long as your sources are uncorrelated, the powers add up
- But if they are correlated, they will more than add at some places and less at others.

Put in other words: you may want to add electric fields or sound pressure, and this does more than add the powers, like in (1+1)^2 = 4 instead of 1^2 + 1^2 = 2. But this holds only when both sources are in phase. If both sources are uncorrelated, the sound pressure will sometime add and sometime subtract depending on the relative phases, the mean result being to add the powers.

This idea of correlation is very interesting and has many consequences, in quantum mechanics as well (probabilities are proportional to squares of amplitudes).

Photodetectors convert a light power (#photons) into an electric current (#electrons), not into an electric power, leading to mistakes.

yeah, like cjameshuff said, it's a question of efficiency, eh?

like, a thirty watt tube amp puts out way more heat than a FET amp that puts out 1000watts.

so, it depends on how much is lost in heat, as to whether the two thirties are as bright as one sixty.

also, from NASA:

http://www.nasa.gov/audience/foreducators/...terference.html

so, two thirties can be brighter than one sixty, eh?

Fantastic, this topic lasted a page before going backwards.

did it?

i mean, theoretically, the waves from the two sources can interfere with each other constructively OR destructively, no?
so, depending on where they are placed, they might sum a dimmer or brighter total brightness, no?
speakers/soundwaves work that way, why not lights/lightwaves?

and, energy lost to heat(and vibration, which is pretty neglible in a light bulb) can make a huge difference in the actual brightness of the bulb. not all sixty watt bulbs are created equal.
that's why fluorescents are so popular, now. a 15 watt bulb can output as much light as a 60 watt incandescent, so obviously two thirty watt flourescents could output more than a sixty watt incandescent, no?

and, two bulbs have more surface area to dissipate heat, so two thirties are PROBABLY more efficient than one sixty, no?
but then, the increased heat in a sixty might cause the filiment to burn hotter, no?

is it really that simple a question? i don't know.

oh, yeah...


p.s. .....eh?

oh yeah, and two bulbs would also reflect off more surface area on the walls, so given equal efficiency, two WOULD be better than one.

You won't get stable - thus usable - interferences from light bulbs because their light isn't correlated, and because wavelengths of 0.5µm give to small interference patterns.