Re: Cree 40-60lm/W LEDs 'in the wild'?

Hi,

> Thanks for the info to clear up my questions. The issue that concerns
> me is the huge spread in LED performance. Even the "high lumen" bin
> has a rather low minimum lumen output. The manufacturers use a mean or
> median number in their advertising, yet the customer has no guarantee
> that they will receive a device as good as the advertised number. If
> the higher numbers are real and can be reproduced, why do the
> manufacturers not use much smaller bins so that customers have a
> better idea of the performance they will get from the LEDs they
> purchase?

You are right, this is little bit confusing but you should know that this is
how the electronics industry works. It is always hard to receive in one
batch only one type of LED, diode, transistor, resistor, capacitor, etc.
etc. They are always sorted after production. In LED business the large
manufacturers can have a few dozens or more bins from a one batch. The white
LED's are sorted by luminous flux, CTT, and typical Vf. From one batch they
get LED's that parameters suits Gaussian distribution or similar one. So
there is always a lot of medium performance LED dies, and little high and
low performance ones (but they are).

Manufacturer can sort them into the bins then. Of course everybody wants to
get the LED's from best bins unfortunately the manufacturer wants to sell
all bins (not only this the best one). So, high power LED manufacturers
offer to the customers so called kits that consist of a number of few
different bins (they are of course sorted and good labeled) and rather do
not sell LED's from only one certain bin. You can buy only the best XLamps
but the quantity and the price will be very high then.

I have consolation for you - in a few years the progress in technology will
enable LED manufacturers to produce their LED's with higher precision than
now. To day we have to manage with this problem (it is possible eg. SONY and
their displays with LED backlighting - they use special driwer that driwes
the LED's from different bins separately in order to receive always the same
white light).


> If LEDs were sold as lamps in the US I strongly suspect the Federal
> Trade Commission would force manufacturers to put either the lowest
> number on the box and in their advertising, or put the full range on
> the box and in their advertising.

You see, the lamp manufacturers buy LED's good labeled so they are able to
put on the box information about typical luminous flux of the LED they use
inside with accuracy of about +/-2,5lm (for XLamps). Of course if they do
not play in this way they should be forced to do this by law.

> This opinion is based on a similar issue involving the difference
> between base-up and base-down performance of CFLs. In that case the
> FTC was going to force the lamp manufacturers to use either both
> numbers or only the lower number instead of only the higher number as
> they had been doing. The issue was resolved by replacing liquid
> mercury with mercury amalgams that significantly reduced the
> difference between base-up and base-down performance.

Intersting. We will see how the things will go in LED industry then.

Regards,

Adam Wilanowski
www.lediko.com




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