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Does anyone know how MCD is calculated?


By whatsnext, Section Light
Posted on Wed Jul 06, 2005 at 05:48:01 PM MST
I need to find a new sourse for LEDS

My old HK led supplier has gone away so I'm looking for a new one if anyone knows of one. I've found a guy selling 3mm 10,000mcd bulbs and I'm wondering if they have the same output as a 5mm 10,000mcd bulb. Or is MCD some sort of surface measurement? Being smaller the 3mm jobs would be nice. 32 degree angle also.
TIA, John.......
Does anyone know how MCD is calculated? | 11 comments (11 topical)

Re: Does anyone know how MCD is calculated? (3.00 / 0) (#1)
by techwolf on Wed Jul 06, 2005 at 12:25:17 PM MST

the size of the case does not matter, output is the same if the rating is the same.




Re: Does anyone know how MCD is calculated? (3.00 / 0) (#2)
by richhagen on Wed Jul 06, 2005 at 04:57:33 PM MST

The Candella is a measurement of the intensity of light at a given point.  A 15 degree radiation pattern LED that is giving off a certain amount of total light as measured in Lumens (The unit of luminous flux in the International System, equal to the amount of light given out through a solid angle by a source of one candela intensity radiating equally in all directions) would have a higher MCD rating than an LED with a 60 degree pattern with the same Lumen rating.  Lumens is total light, Candella is intensity.  Very rarely however do you see a lumen rating for LED's advertised.  A rough comparison for the total light given off can be inferred from the definition of a lumen by comparing the fraction of a sphere that would be illuminated with the source in the center for each distribution pattern and multiplying by the intensity of the light for each case.  Of course, depending upon the application, the distribution pattern may make a huge practical difference between the particular LED's.  Rich
'A Joule saved is a Joule made'
[ Parent ]


Re: Does anyone know how MCD is calculated? (3.00 / 0) (#7)
by ghurd on Thu Jul 07, 2005 at 07:43:58 AM MST

A simple way to think about it.

MCD and viewing angle are VERY related.  
Like a Mini-MagLight with the removable front lens and reflector.
Go out after dark, 100' from your house.
Focus the beam as tight as it will go. Shine it on the house. Quite bright. High MCDs.
Focus it wider. Shine it on the house. Not as bright. Less MCDs.
Remove the reflector. Shine it on the house. Very dim. Very low MCDs.

Same bulb and batteries, so the lumens (total light) is the same.
Just depends on how it is spread out.
The MCDs (intensity) changed.

A laser has great MCDs, but it is useless as a flashlight or area light.

The viewing angle is usually listed at "2 theta half degrees", meaning half the total light falls in a circle that many degrees.
A really bright sounding LED with a viewing angle of 10' is probably not so bright.

(Start Rant)
And many (most?) No-Name LEDs are very over rated. In MCDs and viewing angle.
Often an entire production lot will not have a single LED meeting the rated specs.
I even had a sample batch with 20% having the polarity reversed!

Don't even get me started on color ratings! Had a sample batch that I thought they actually sent blue instead of white, but was basically informed "What do you expect for that kind of price?"  And the price wasn't very good.

The high wattage type, like 1/2, 1, and 3 watt, are LESS efficient than a decent incandescent bulb. A waste of money and power, except in very limited applications.
(End Rant)

So it depends on what you want to do with them.  20' is nice in a flashlight. 60' is nice for an area light. Name Brand stuff is better.

G-

Ghurd.info
[ Parent ]



Re: Does anyone know how MCD is calculated? (3.00 / 0) (#3)
by Trivo on Wed Jul 06, 2005 at 07:57:33 PM MST

this mob will send to you direct http://www.hebeiltd.com.cn/



Re: Does anyone know how MCD is calculated? (3.00 / 0) (#4)
by whatsnext on Wed Jul 06, 2005 at 09:49:02 PM MST

Trivo, I've heard of this guy, how is he? My old supplier was very good if not too good at engrish. Plus $16.50/100 delivered was kind of nice.
John.......

[ Parent ]


Re: Does anyone know how MCD is calculated? (3.00 / 0) (#10)
by whatsnext on Thu Jul 07, 2005 at 09:57:40 AM MST

I just found my old guy. Not that big a selection but I like his ultra bright whites.
http://www.b2cdirectly.com/
He has some nice flashlights also.
Thanks Guys, John.....

[ Parent ]


Re: Does anyone know how MCD is calculated? (3.00 / 0) (#5)
by pyrocasto on Wed Jul 06, 2005 at 11:35:20 PM MST

I think this guy is one of the cheapest I've found: http://4daily.com/?ref=158375

leds are usually rated MCD, but the bright Luxeons are rated in LM.



Re: Does anyone know how MCD is calculated? (3.00 / 0) (#6)
by wooferhound on Thu Jul 07, 2005 at 06:35:37 AM MST

Interesting website link there
  but it's not about LEDs . . .
W o o f -={(

[ Parent ]


Re: Does anyone know how MCD is calculated? (3.00 / 0) (#8)
by pyrocasto on Thu Jul 07, 2005 at 09:14:18 AM MST

LOL! Thanks Woofer. Didnt mean to spam the boards.

Here is the real link: http://www.hebeiltd.com.cn/?p=z.pricelist.led.diode

[ Parent ]



Re: Does anyone know how MCD is calculated? (3.00 / 0) (#9)
by DanG on Thu Jul 07, 2005 at 09:31:28 AM MST

Ready to be swamped with possibilities? EBAY Search
--> http://tinyurl.com/cf359

Take what ghurd mentioned (ranted?) as gospel, the 1000X profit in reselling manf. errors, culls & underspec devices tempts even saints : )



Re: Does anyone know how MCD is calculated? (3.00 / 0) (#11)
by ghurd on Thu Jul 07, 2005 at 10:13:10 AM MST

And all those were imported by me directly from various factories in Asia!
G-
Ghurd.info
[ Parent ]


Does anyone know how MCD is calculated? | 11 comments (11 topical)
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