On 27/09/2013 14:46, William Sommerwerck wrote:
Have you calculated whether you can cram enough LEDs into that space to
get the same brightness level as the discharge lamp? Or are you
expecting to learn from the test?

I'd like to point out that is no such thing as -- nor can there be -- a
white LED. LEDs are necessarily limited to a narrow band of wavelengths.
* All (???) white LEDs are (I assume) a blue LED with a
yellow-fluorescing phosphor. **

This /looks/ white to the eye, but the red and green wavelengths needed
for color reproduction aren't present.

Unless your white LEDs contain red, green, and blue LEDs, I don't think
this is going to work.

* This is actually a good thing if one is trying to match a specific
color space, and you can manufacture LEDs whose wavelengths correspond
to the three primaries.

** I'm thinking of indicator lights and such. Lamps to replace
incandescent lighting would necessarily have to put out red and green,
or colors wouldn't look right.

Its not possible to do any calculation as to brightness because it is
impossible to find the true loss of light from a conventional
distributed ie not point source discharge lamp source and non ideal
reflector, I would guess that 2/3 of the rated light does not get into
the apaature and then how to calculat the proportion that is at such an
angle to the light tunnel to the active chip and multiple reflections
that little of that gets to where it is wanted, axially along the 2
inches or so of narrow diameter light pipe .

As for colour rendition it is unlikely to be any worse than the current
situation of having to place a rose-pink filter over the projector lens
to get some red into the image as the lamp must be too far into the blue
end of the spectrum tio be compensated for in the setable timing of the
colourwheel.

So in both cases very much a suck it and see, seat-of-ones pants
situation, but worth a go, if you've seen the price of these supposed
replacement discharge lamps