"Jay" wrote in message
om...
(Jeff Peterson) wrote in message
om...

In order to get the wide angle coverage you need, you can either use a
large number of LEDs, each with a narrow beam or you can use the same
number of LEDs each with a broad light beam. When you grind the front
off the LEDs the forward-directed brightness (officially called the
luminous intensity [in milli-candella, aka mcd] ) will be decreased
because the light is no longer directed forward but is spread out
instead. The total amount of light emitted (officially called the
luminous flux [in lumens, aka lm]) is not affected by grindind off the
front. This means you need just as many ground-off LEDs as you do
intact ones. The advantage of grinding them off is that you dont need
to go to all the trouble of pointing them every which way. As far as
scratches go, yes, they do diffuse the light output, and that's just
what you want.

You save having to do as much pointing but you have to grind and
POLISH each one. The scratches cause a loss in the total flux. Look
at what you have to do to prepare the ends of fiber for installation
of connectors, and thats even for the longer wavelengths in IR.

i noticed this coincidence: all these devices seem to use about the
same current, 20 ma. so very likely they have similar flux. i think
the more expensive ones are the ones that have the LED chip located
very close to the focus of the hemispherical lens....these have the
narrow beam that gives them high mcd numbers. if you are grinding the
dome off, it doesnt make sense to pay extra for this.

They use the same current because its the same little chunck of Si.
The cost of molding the lens doesn't vary much depending on the angle.


This is correct. The flux, or total light output, does not change. We
either spread it out, or concentrate it.


What you're paying all the money for as I understand it is:
1) Pick of the litter, the semi-conductor die vary in efficiency and
are binned. You pay more for the really good one, and less for the
others.


Not quite the whole story. In ascending order of output AND price:
1. Gallium Phosphide
2. Gallium Aluminum Arsenide
3. Allium Indium Gallium Phosphide (AlInGaP, pronounced like the
abbreviation)
4. Indium Gallium Nitride (InGaP, ditto)

All of the major die manufacturers bin their die. I won't tell you the
ratios of brightest to dimmest, quantity-wise, but reputable LED
manufacturers are interested in producing product yielding the most
efficient use of the wafer. Specifying bins (bright OR dim ones) dictates a
significant price penalty to the user. Naturally, over a product lifetime,
the entire wafer goes up in intensity, but the primary factor in retail
price is the wafer material, shown above.


2) New process technologies- All these really bright LEDs are the
result of recent changes in semiconductor processing, so there is less
competition because less guys can make them.

Yes, and add that material #4 is the subject of a patent dispute, only
recently negotiated (or subverted).

Regarding position lights, commercially-available 3mm (aka T-1) LEDs are
possible at 500 mcd over a 50-degree angle. There are some VERY high
intensity LED packages not available to the retail user (yet), e.g. the red
and blue lightheads and in unmarked cruisers. Yes, these are LEDs, not
strobes.

Bernie
in the LED business for 20 years
remove my age to reply directly