On Sun, 30 Jan 2005 14:20:22 -0600, wrote:

An artist friend of mine asked me to help her with a project she is
designing.

The project is an atrium wall (ten foot above the floor) with an array
of blown glass elements(each about ten inches across). The elements
are to be lit from behind and the lights are to dim and brighten in a
random pattern.

She asked me about a way to hinge the glass elements so people could
replace the light bulbs, but she wanted the mounting to be hidden so
that the elements would appear to be floating.

I thought about this and came to the conclusion that it would be
easier, to never have to replace the bulbs.

I am wondering if a cluster of LEDs could be used in place of the
incandescent bulbs. It would cost more, but that might be offset by
much lower wiring and maintainance costs.

Is this possible, do these new high output LED have enough jazz to
replace a 25 0r 40 watt incandescent bulb.?

Are they dimable?

How much extra would be involved in the control circuitry to drive the
LEDs?

Luxeons are the brightest LED's by far. They're about twice as
efficient as indandescants, so a 3-watt Luxeon would be equivalent to
about 5 or 6 watts of incandescant light -- if it's white light. If
it's colored light (red, green, blue, etc) then the Luxeons are more
effective: a 1-watt red lux is about equivalent to the 12-watt 1157
brakelight on a Chevy truck. A 3-watt red Luxeon probably would be
comparable to a color-filtered 25-watt incandescant. Color filters
significantly reduce the brightness of incandescants, but colored
Luxeons emit all of their lumens as light of the particular color at
hand -- no filter.

3-watt Luxeons are about $8.50 each. Lifetime to 50% brightness is
20,000 hours if run at 1 amp, 50,000 hours to 70% brightness if run
at 0.7 amps. Yes, with electronics they are dimmable -- and they
don't change color when dimmed, liked incandescants do. With
multiple colors, both brightness and color could be varied.
Electronics for use on mains could be very inexpensive if optimal
efficiency isn't a big deal.

Depending on the situation, you may find that the light can be
directed well enough with available inexpensive ($3.50) molded
collimators that you don't need as many watts (lumens) as you think
-- particularly if you use colors.

There is an upscale apartment in London (Chelsea) that did some
interesting illumination with Luxeons. Check out
http://www.thevospad.com/gallery.htm

Email me if you'd like to discuss Luxeons and/or elex to drive them
further. I'm fascinated with them!