led intensity measurement

hi
anyone know about MCD. the rating for the led intensity.
i want to compare two kind of led and i don't know meaning of 2500mcd.
plz help
thanks

2500mcd= 2500milicandela

what is minicandela and how i can measure it?

Candela some standard unit for light..,sometime is see some standard use LUX or Lumens...i never have experience for light measurement....but i think ready on market CANDELA Tester.

BR

CANDELA or Candle in english, is a fundamental measurement unit, like Kilogram, meter, second. It's primary so it's not related to other one unit.
The SI is based on Meter, Kilogram, Second, Ampere, Candle.
Candle is the "radiate" light over a solid angle. Hard to measure! More easy the measurement of the light flux, then knowing the radiate angle and the distance, you may calculate (as a post processing of the measure) the radiated light.

what amount of 1 candela.
i want to undrestand the amount of light for compare.

Good Explanation and Usefull Sergio : )

BR

Added after 5 minutes:

To Sergio Mariotti...
Can u tell me Imagination value (candela) for led in some latest GSM phone..?
Coz i want some view good value Candela in LED,for some my applicaton.

Before and after thanks Sergio...

BR

Here's some basic info on illumination terms:
http://www.theledlight.com/lumens.html

One can add, that:
1 Candle is a energy density (W per stereoradian=W/Sr) of electromagnetic valwe with 5,4∙ 10^5 GHz freqwuency giving the power of 1/683 W/Sr

One can say that is is complicated.
OK, let as take as a reference a definition of 1 meter (unit is commonly known and should be be a pice of cace) here it is:

1 meter is 1 650 763,73 periods of electromagnetic valve that is emitted by the crypton 86 atom, during its electron position change from level 2p10 to level 5d5.

Buy a light meter from a photographic store. They are cheap and probably somewhat calibrated.

Biff44..,what unit value in Fotograph Light meter ?

BR

The home reference for a candela can be a 21W "compact fluorescent tube".
Is written on its body that 1200 lm are emitted when lamp is supplied from 230V.
I think that the real lm value may range between 900-1300 so one can assume, that average 1000 lm (rather than 1200 ) is emitted by the real lamp .

The lm = candle *stereoradian / square meter

Let us assume, that all measurements we will perform at 1 m distance.
From stereoradian definition we know that the r^2 surface is "seen" by stereoradian at the distance = r. At 1m distance from the lamp the stereoradian "see" a surface of 1 m2 .
We assume, that the lamp emitt the light in all direction, what means, that at 1 m distance the light will be equally distributed over the surface of a ball.
Let us take a sphere (ball) with 1 m radious.
From mathemetic we know that the surface of ball = 4 * 3,14 * r ^2
Hence radiated light = 1000 lm / 4Π = 79 Candles

Now you know that the lamp emitt 79 Cd so you can calibrate your Fotograph Light meter.
Measure the light intensity at 1 m distnce (or any other but during each measurement the same) and record that the reading is xx for 79 Cd.

But remember:
1. Light meters usually have a logarithmic characteristic.
2. The room shoudl be black to avoid reflections
3. lux (not Cd) are measured by your light-meter!
lux = (lm / m^2)
4. You can calibrate your luxmeter taking measurement from different distances. For example at 2 m you read on your lightmeter the equivalent od 20 Cd from 1 m distance.
(2x grater distance = 4 times grater the sphare surface)
5. While measuring the light from the LED you should take into consideration, that usually LED characteristic is a beam like (for example 30 - 100 degree)

Lux is more practical than Cd , because measured value (lux) is the usable lumination at given point rather than the TOTAL light energy emtted from the light source .

Does 30-40% accuracy satisfy you ?
Good luck.

thanks a lot.
this is very complete.
but a question: are you have a book to refer me to this.
thanks

No, I do not have a book.
I get support from www asking in google for :
"candela, lumel, SI, unit "
But there I found the definitions only.
All conclusions and calculations I have done myself.

just a simple explanation of the ligth formation in light emit diod[LED].
LEDs are semiconductor diods that when we apply tensionin in direct direction it emit ligth in the PN junction.
when a direct tension is applied in PN junction the electrons establish in the anodic region and the gaps in the catodic region.many of the electrons don't have enough power to abandon completely their original atoms,theirfor they are attracted again by them to their original valencia orbits. it's exactly in this moment that the photons are release(ligthing power).

at the :

http://www.gizmology.net/LEDs.htm

you can find illumination formulas for led