Re: LED intensity/angle mcd?
- From: Spehro Pefhany <speffSNIP@xxxxxxxxxxxxxxxxxxxxxxx>
- Date: Thu, 18 May 2006 18:34:37 -0400
On Thu, 18 May 2006 22:51:21 +0100, the renowned Pooh Bear
<rabbitsfriendsandrelations@xxxxxxxxxxx> wrote:
RHRRC wrote:
Pooh Bear wrote:
wrongaddress@xxxxxxx wrote:
Looking at the specs for 3 red LEDs, I'm wondering which would be the
better choice for maximum brightness.
Allied part number 670-1257 which claims to be a 400mcd device with a
viewing angle of 60 degrees at 2x theta. Cost is 72 cents.
A second part 670-1224 claims to be a 1800mcd device with a viewing
angle of 30 degrees at 2x theta. Cost is 50 cents.
A third device is 670-1226 claims to be a 1200mcd device with viewing
angle of 30 degrees at 2x theta. Cost is 31 cents.
I'm not sure what 2x theta means,
It means 2x the 'view angle' theta e.g. 30 degrees, so it's talking about a cone
of light with a sixty degree included angle ( for theta = 30 ).
but I think if the angle is twice as
wide, the intensity should be 1/4 as much, so that a 1800mcd device at
30 degrees would be the same as a 450mcd device at 60 degrees?
For the same led 'chip' inside the led you got it.
Why would the the 400mcd device sell for 50% more than the 1800 mcd
device which has more total output?
No idea.
Would the more expensive device be the better choice?
What do you actually want ? A narrow angle led or a wider one ? Whichever's more
suitable for your application is better.
Graham
The ratio of the intesities for a given led die with different theta's
is the inverse of the ratio of the square of the tan of each theta.
Since tan15=0.268 and tan30=0.577 we would expect the narrow angled
device to be
(0.577*0.577)/(0.268*0.268) =4.64 times 'brighter' than the wider
angled device.
Which indeed seems to be the case here.
Graham
It's diffused too, which should make it even worse.
Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
speff@xxxxxxxxxxxx Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com
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