Hi Ryan,



(Ryan Young) wrote in message . com...
(Jeff Peterson) wrote in message . com...
just a couple of suggestions...

-if you grind the domed front off an LED the light pattern becomes
broad instead of narrow. that seems easier than trying to arrange
many narrow angle patterns to overlap.

You could do this, but it would be wrong. Spreading the beam in this
manner makes it more diffuse. Plus, all the scratches you'll induce
in the lense will make light transmission less efficient.
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.




-before you grind off the front, spray paint the entire plastic bit
white. then, after grinding, all the light has to come out the ground
off end.

More like get absorbed by the paint before it ever gets out of the
packaging. Another idea I wouldn't pursue.


white paint is pretty reflective, and not too absorbing. I think white
paint would do more good than harm. if you are really fussy you could
silver the outside. or dont. I think this only makes a 10 percent
difference.




-the place to get cheap LEDs by the 100s is ebay. maybe 20 cents each
for ultrabrights.

Depends on what's meant by ultrabright. Check the MCD numbers. More
is better. 12000 mcd green LEDs run about $1.20-$1.50 ea, but yes,
there are some 10,000 mcd LEDs running about 20 cents, and that's
probably plenty bright enough. Meself, I wouldn't futz with anything
dimmer.
what you really want is a high mcd number AND and a wide beam. that
gives you high luminous flux (aka total light output). generally LED
vendors are charging a premium for the very narrow beam units...the
ones with the highest mcd values. so i would avoid these, and try to
get the most light output for the dollar.

the auction below offers 100 each red LEDs, 5000 mcd, with a veiwing
angle of 15 degrees for $21.00 including shipping

http://cgi.ebay.com/ws/eBayISAPI.dll...m=3816545 720

by the way, i wish the ebay vendors would quote luminous flux (as
lumileds does).

instead they quote intensity. worse, they use a variety of
definitions of the beam angle. some give the full angle of the beam,
others give the half angle. some give a number and dont say which.
also they dont say if that angle is the half power point of the beam
pattern. so its a bit hard to get the flux from their numbers.

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.



So, one good tip out of three, IMHO. Better than the RAH average.
If I counted such things, the number would be three...
-Jeff