Referring to my Underfloor lighting post below, another thought is a "flood"
of closely-packed LEDs behind a diffusor.
Will be very inefficient compared to a discharge light
sources UNLESS you can match the color of the LEDs to the
transmission wavelength of the tile.
Can LEDs be thought to have a (forever) lifespan?
No. That is hype.
What causes an LED to "burn out"?
They usually don't burn out in the normal sense, they just
have reduced light output over time. Deprecation rates
depend upon the type of LED, the operating current and the
temperature.
Can a lower than the LED's spec firing voltage increase life?
LEDs do not have a "firing voltage." You can increase life
by reducing the operating current, but that will also reduce
light output.
I admit that
I do not know when an LED starts emitting light. Is it a step function?
i.e. lights up at a specific voltage, thus is not dimmable??
Some guidance/pointers appreciated.
You should look at some good LED data sheets. Perhaps some
from Lumileds. They show light output and forward voltage as
a function of operating current. From a practical point of
view there is no minimum current for generating light,
though there is a minimum voltage required to have current
flow.
LEDs are easily dimmed by varying the current. Unlike
discharge lamps, you can run them from a voltage source, but
they will be much easier to control if run from a current
source or at least with a current limiting resistor in
series with a voltage source.
--
Vic Roberts
http://www.RobertsResearchInc.com
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