MCD?

Dr. Snuts, M.D. · Post by **Dr. Snuts, M.D.** » Sun Dec 28, 2008 1:36 pm

Hi all, I had planned on buying a bunch of cheap LEDs and experimenting and such when I came across something I was not familiar with. What does MCD mean? As in a 7000mcd vs. a 10000mcd?

USS Atlantis · Post by **USS Atlantis** » Sun Dec 28, 2008 2:02 pm

Mcd is the Millecandela rating

This is a function of brightness - it relates to Lumens (intensity of light bulbs) on a mcd/angle of view ratio

There's a whole series of calculations and what-not to measure intensity of light - and some of it is very subjective (perceived luminosity)

Simply put, the higher the mcd rating of an LED, the brighter it will appear to you when looking at it within the viewing angle

So a 5800 mcd LED with a 100 degree angle will appear 1/2 as bright as the 11,000 mcd LED with a 30 degree angle one when viewing within it's viewing angle, but you'll be able to see the light clearly from the 5800 mcd one from a much wider angle of view

Dr. Snuts, M.D. · Post by **Dr. Snuts, M.D.** » Tue Dec 30, 2008 4:23 am

Thanks Atlantis. That makes sense now. Does the higher MCD require a greater power source? Do they burn out quicker?

USS Atlantis · Post by **USS Atlantis** » Tue Dec 30, 2008 5:11 am

No and no

The higher mcd rating LEDs are usually more efficient in energy usage - the 5800 mcd White LEDs I use are still only using 3v @ 20ma - same as those 30mcd Radio Shuck LEDs

And the MTBF (mean time between failure) is the same across the board for virtually all LEDs

If you want more light, go with the higher mcd ratings - you won't lose anything by doing so

jwrjr · Post by **jwrjr** » Tue Dec 30, 2008 10:09 am

A comment on the last post - higher MCD ratings do not necessarily mean higher current consumption. However, certain types of leds ( especially Luxeons or the equivalent) take a lot of current. The way to be sure is to read the spec sheet.
One other thing - you don't have to run a led at its max rated current. A trick that is useful for battery powered installations is to take a higher output led and run it at lower current.

USS Atlantis · Post by **USS Atlantis** » Tue Dec 30, 2008 7:28 pm

jwrjr wrote:One other thing - you don't have to run a led at its max rated current. A trick that is useful for battery powered installations is to take a higher output led and run it at lower current.

Addendum to JW's post

There's a couple calculators on This Page that will allow you to custom set the output of the LED, and it'll let you calc the required resistor to do that

Running the LED at less than normal brightness will not only extend the battery life of your power source, it'll also extend the life of the LED

Example: Yes, I get the 5800 mcd whites, but I run them at about 2000mcd for lighting windows with Fiber