Physics Question ???

Heliospherez · 3 Apr 2006 at 17:30

Is there a measurement for darkness ? Have been discussing this at work (with a number of doctors/professors) - so give me some mature suggestions if you have any......

And before anyone goes into one about light, lux, lumens, candela, electromagnetic spectrum, radiance, watts, human visible wavelengths, polarization, refraction, talbots or anything to do with the absence of photons (or brightness) - Yes, I know we can measure light, and I know darkness is the absence of light - but do we have a measurement for darkness (as in an SI unit or similar)

I have trawled the net (and wikipedia mostly) for all the references to darkness and blackness - so any ideas ?

clv101 · 3 Apr 2006 at 17:34

I'm not sure I understand... lightness and darkness are the same thing, on the same scale. Why would there be two ways of measuring the same thing? Do we have a hotness and coldness scale? No, just a single temperature scale.

philio16 · 3 Apr 2006 at 17:36

clv101 said:
I'm not sure I understand... lightness and darkness are the same thing, on the same scale. Why would there be two ways of measuring the same thing? Do we have a hotness and coldness scale? No, just a single temperature scale.

Exactly! Can't see there being one myself

KaHn · 3 Apr 2006 at 17:38

Surely this is just like the kelvin scale for hear (or measure of mean kinetic energy), the light scales you have mentioned all must go to an absolute zero?

KaHn

Heliospherez · 3 Apr 2006 at 17:39

But when I say Darkness, i don't necessarily mean as in light or air. It could be liquid, solid etc - who knows ?
What is the scale to measure the darkness of liquids and solids then ?

MrMatteh · 3 Apr 2006 at 17:49

Mikol said:
The only thing I can think of is absorbance. Ie. with a spectrophotometer you can measure how much it is absorbing the light and in turn, it's darkness (in a sense).

from what i understand from your question, the 'darkness' or an object - say a white box compared to a black box - would be measured by the absorbtion of the incident light, like Mikol says

Arcade Fire · 3 Apr 2006 at 18:14

It's as has been said - you measure how dark something is by the lack of light emitted from it, just as you measure how cold something is by the lack of heat energy that it gives out. So 'darkness' is measured in Candela, if anything at all.

There are only seven SI units, which are

Metre (length)
Second (time)
Kilogram (mass)
Kelvin (temperature)
Ampere (current)
Mole (uh... amount of 'stuff')
Candela (light intensity)

It's possible that I may be a little hazy on the last two

KaHn · 3 Apr 2006 at 18:19

Arcade Fire said:
It's as has been said - you measure how dark something is by the lack of light emitted from it, just as you measure how cold something is by the lack of heat energy that it gives out. So 'darkness' is measured in Candela, if anything at all.

There are only seven SI units, which are

Metre (length)
Second (time)
Kilogram (mass)
Kelvin (temperature)
Ampere (current)
Mole (uh... amount of 'stuff')
Candela (light intensity)

It's possible that I may be a little hazy on the last two

http://en.wikipedia.org/wiki/SI_units

KaHn

aardvark · 3 Apr 2006 at 19:03

colour is defined in many ways - RGB, Lab, xyz - black is defined in these systems, along with all other colours (and is used all the time to quantify colour of displays, textiles, printing etc...) - find a book on colour physics - there is lots of maths involved though.