LED-Brightness: 10000mcd vs. 20000 mcd

Hey guys,

got a littel greenhorn-question /ubbthreads/images/graemlins/smile.gif

How bright is a 10000mcd LED? I don't have a clue...comparisons?

I'm thinkin about constructing a LED-lamp as an ambience light using 30 LED with a 10000mcd each.
Is this enough? or should I better use the 15k/20k mcd?

(lamp: 9 seperated lightsources with 3 LEDs each)


Thanks a lot /ubbthreads/images/graemlins/smile.gif

friendly regards, Deepsky /ubbthreads/images/graemlins/help.gif

mCd = 1/1000 Candela, candela= candlepower.

So think of them as candlepower as this forum got its name.

But, Candela is measure of intensity, if you focus the beam of an LED narrower the Cd figure goes up though its the same amount of light just in a narrower beam.

So look at the beam angle as well as the Cd number.

One page explanation of light measurment units

http://www.holophane.com/product/pdfs/6.pdf

HTH
Adam

excuse me, but you just mentioned everything I already know /ubbthreads/images/graemlins/smile.gif
not THAT green /ubbthreads/images/graemlins/wink.gif

So I want to know if theres a comparison LED 10k mcd to normal light?

If you wnat to use it as a lamp, how bright is a LED with 10k mcd or should I use 15-20k?

See first post!

Thx,

Deepsky

Hello Deepsky,

I believe 10000 mCd is the same as 10 Cd.

I know that 10 Cd = 10 lux (at 1 meter).

The square root of 10 is about 3.16.

If you look at Doug's (Quickbeam) Output vs. Throw charts in the reviews section, you can compare to lights with a throw of around 3. You may be able to find a light that you know of or have. That should give you some idea of what you are looking at.

Tom

[ QUOTE ]
excuse me, but you just mentioned everything I already know
not THAT green

[/ QUOTE ]

*bites tongue*

[ QUOTE ]
So I want to know if theres a comparison LED 10k mcd to normal light?

[/ QUOTE ]

Refer you to the above linked PDF, your falling into the LED marketing trap.

To truly compare light sources you need to compare Lumens, total light output, NOT Candela which is a directional measurement capable of being manipulated.

So impossible to compare a 100W General Lighting Service, GLS, lamp measured in Lumens with an LED wih only Candela quoted.

Before someone points it out it is possible to extrapolate rough Lumen figure knowing Cd and beam angle figures but it is very rough.

Typical lamps that may be quoted in Cd are MR16 reflector lamps, as they have a known beam angle.

According to


http://www.lrc.rpi.edu/programs/nlpip/lightingAnswers/mr16/performance.asp


[ QUOTE ]
Beam angle and center beam candlepower:

Beam angle and center beam candlepower (CBCP) are performance parameters that characterize the beam appearance and the maximum beam intensity of a directional lamp. According to manufacturers' catalogs, the beam angles of MR16 lamps range from 7 to 60 degrees, and their CBCP may range from about 500 up to 15,000 candelas, depending on different wattage and beam angle combinations.

[/ QUOTE ]

and thats full size Candela not milicandela.


[ QUOTE ]

If you wnat to use it as a lamp, how bright is a LED with 10k mcd or should I use 15-20k?

[/ QUOTE ]

Look at Beam Angle that suits your application.

LEDs unlike halogen dim with out changing colour, so if its too bright you can dim them, overdriving a too dim LED array is a bit harder...

Hope this helps, learn something new everday ;-)

Adam

ok right. I know, that cd depends on the angel and W, ...right?!

http://www.led1.de/shop/product_info.php?products_id=41
http://www.led1.de/shop/product_info.php?products_id=50
http://www.led1.de/shop/product_info.php?products_id=327

These are the ones, im talking about. What is a bit surprising, that they run all at 3,4V, don't differ in the eletric-current and have the same angle,...
but differ in intensity. How can that be?

So which should I buy?!

/ubbthreads/images/graemlins/smile.gif help again /ubbthreads/images/graemlins/smile.gif => a lamp with 27 led splitted in 9 sectors with 3 each

DeepSky

[ QUOTE ]

These are the ones, im talking about. What is a bit surprising, that they run all at 3,4V, don't differ in the eletric-current and have the same angle,...
but differ in intensity. How can that be?


[/ QUOTE ]
Easy. They use different bin blue dies which have different outputs. For example, Cree grades their dies (XT-15 = 15mw, XT-18 = 18mw, XT-21 = 21mW, XT-24 = 24mW, etc). A blue die with more output results in a brighter white LED.

mabyee a brief explanation of what you are trying to do would make an answer appear. if the viewing angles are all the same, most people here would say, get the brightest ones. HOWEVER. if you are using 30 LED's to light a small area, and you are either filing down the LEDs or putting them inside some kind of filtered container, and you need it just to get around, then the 10kmcd LEDs would work.
Just give us an idea of what you are trying to accomplish.
Jeff