Light Questions

[T-Nemesis]

I'm sorry if this is the wrong place for this thread, I couldn't figure out where it was best suited

 

I have two questions about light.

 

My first question is, is light measured in anything? Sound is measured in decibels, heat in celsius/farenheit, but I've never known a measurement for light.

 

My second question is, theoretically is there a limit to how bright a light can be?

 

Thanks

[Kyrisch]

Heat is not measured in Celsius/Fahrenheit; it is measured in calories. Temperature, something entirely separate but related, is measured in Celsius/Fahrenheit. Adding a half calorie of heat energy to a gram of water will not cause the temperature of that volume to change at all, due to water's high specific heat.

 

The wavelengths and amplitudes of light waves are measured with distance measurements. And I think the brightness of light depends on the amplitude of the wave, in which case, theoretically, there is no limit.

[Mobius]

Hmmm I prefer to measure heat in Joules.

 

Light is measured by wavelengths and amplitudes as Kyrisch said. The wavelength is related to the frequency as wavelength * frequency = speed.

Red and yellow are the low frequencies of (visible) light while blue and violet are the high frequencies of (visible) light.

[T-Nemesis]

Okay, I see. Thanks for clearing that up

[Mart]

Adding a half calorie of heat energy to a gram of water will not cause the temperature of that volume to change at all, due to water's high specific heat.

So what's the minimum number of calories that will do the trick?

[j_p]

The measurement analogous to decibels would be lumens, wouldn't it?

 

T-Nemesis is looking for a unit of measurement for 'how bright' the light is; that is, its intensity, not its color.

 

Sorry, I was wrong; the unit for intesity of light is candela; lumen is flux and lux is illuminance.

 

http://www.unc.edu/~rowlett/units/sipm.html

 

http://physics.nist.gov/cuu/Units/

[Kyrisch]

1 calorie, in response to Mart.

[MattC]

1 calorie will raise the temp of 1 gram of water by 1 degree c. That's how a calorie is defined.

 

It is not true that .5 calories will do nothing. It most certainly will! That energy does not just sit in some limbo state, non-existant until another half calorie comes along - it increases the energy with which the molecules of water bump into each other and vibrate, and the result is, in the case of an addition of .5 calories added to 1 gram of water, an increase in temperature by half a degree celcius.

[Kyrisch]

er yeah, sorry, I mixed up my examples...

 

A better, and more correct, example is how ice water will stay at a semi-constant temperature even if one keeps adding heat energy to it; the temperature will continue to stay semi-constant until all the ice has melted.

[CuriousMan]

Light is a electromagnetic wave that has its frequency and length,it is clear. If it is so can a man create artificial sunlight? I do not mean the electric bulbs that when are heated emmit el-mag waves. I mean a sunlight generator that would generate electromagnetic wave of the same length and frequency the sunlight has. And about the intensity of light. On what the intensity of light depends,on the amplitude of the wave or something else ? Anyone here knows what the amplitude of sunlight is in a sunny clear day?

[BhavinB]

Light Intensity has many units, such as Lumens. However, in research the widely used units are W/m^2 (power density).

 

The intensity of lighting at the earths surface is 1000W/m^2.

Though we may be able to reproduce the spectrum of light the sun emits, there is no way we can to some practical degree reproduce that intensity (yet).

[EvoN1020v]

Light is an electromagnetic wave where the maximum speed is rounded to approximately 3.0 x 10^9 metres per second. Also in real life, amplitudes in light wave don't remain constant over long distance with no objects intruding. The waves would be called "damped harmonic oscillator" where the amplitude decrease over a period of time. You would use sin or cos functions to define the wave of light. Use this equation: A=Aoe^-kt. The e is the natural exponential so the value is 2.7182818...

 

Hope this helps.

[timo]

Seeing the chaos that broke out in this thread, I think it´s a good idea to emphazise the answer which came closest to the intend of the original question:

[...]the unit for intesity of light is candela; lumen is flux and lux is illuminance.

 

http://www.unc.edu/~rowlett/units/sipm.html

 

http://physics.nist.gov/cuu/Units/

 

 

@others who want to measure temp in celsius or fahrenheit and heat in calories: That´s possible of course. You can as well measure energy in snickers and mass in pizzas. But neither of them are conform with the international standard units (see links in quote above or http://en.wikipedia.org/wiki/SI_base_units).