Candela and Lumen are not even measuring the same thing !

Lumen is the *total* amount of light from a specific light source
*no matter in what direction* (or the sum of all directions).

Candela in strength of the light from a specific light source
*in a well specified direction* (point in space). A Candela
figure is meeningless if there isn't also a direction specification.

Let's compare two lamps with the same wattage (say 60W).
One of them are of the standard round type, and the other
is the built in reflector type.

Now, both lamps produceses the same *total* amount of light
(more or less, there will be some losses in the reflector),
and therefore has the same *Lumen* figure.

On the other side, the reflector lamp has a much larger
*Candela* figure then the round type, *if* measured
right in front of it. Can be a magnitude in difference
depending on how the reflector is made.

So there is no way to make a *generic* conversion formula
between Lumen and Candela. And if so, why have both in the
first place ? :-)

Well, you could look at the Lumen value to be the integral
of the Candela value over the whole 3D-space, in a way...

Jan-Erik.

Alex Harford [mailto:alex@ALEXHARFORD.COM]

> On Thu, 2003-09-11 at 05:04, Quentin wrote:
> > Same data sheets give LED intensity as luminous intensity as 'nnn mcd'.
> > Others give it as luminous flux as 'nnn lm'.
> > How do you convert from the one to the other and what is the difference?
>
> I believe that mcd is microcandellas and lm is lumens.  Google may have
> that conversion in their search '1 mcd in lm'.  If not, I'm sure there
> are references on the web.

--
http://www.piclist.com#nomail Going offline? Don't AutoReply us!
email listserv@mitvma.mit.edu with SET PICList DIGEST in the body