Hmm, presumably though, they need to use power fromsomewhere if going out
past Mars. The supply of spares will obviously need sorting out as well.
somehow one never sees this sort of problem depicted.
Brian

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From the Sofa of Brian Gaff Reply address is active
"Jeff Findley" wrote in message
...
In article ,
says...

Surely they should have grown Rocket Lettuce?
all this growing with leds, I'd be a bit worried about this way of doing
things.
Soory mate, no food, the leds need replacing.

LEDs have an extremely long lifetime, far better than other lights.
That and they don't tend to fail completely. Their light output just
tapers off slowly with use. So, I'm not sure what the worry is here.

http://digitallumens.com/resources/b...led-lifetimes/

- Incandescent bulbs can range from 750 hours to 2,000 for ?long-
life? versions.

- Compact fluorescents (CFL) bulbs have claims of up to 10,000-hour
lifetimes.

- Industrial HIF and HID lamps are approaching 20,000-hour lifetimes.

Now onto LEDs. When we talk about LED lifetime, we mean the
period after which the LED light puts out only 70% of its
original light. (Note: this is not total failure, just the
point at which the system emits less light and a fundamental
difference in the definition of ?lifetime? largely because
LEDs are a fundamentally different illumination technology.)
In technical parlance, this is the L70 rating and can range
from 50,000 to 100,000 hours based on design and operating
temperature. Even after that time period, the LED light
will continue to operate for years; just not at 100%.

Note that 50,000 hours is over 11 years with a 12 hour a day duty cycle.

So, for a very long mission, say 11 years, you just design the system so
that it can adjust the light output of the LEDs over time. Run them at
less than full brightness to start with, and with time, keep slowly
increasing the power to them to maintain the desired brightness. At the
very end of the design lifetime, you can't increase the power to the
LEDs anymore without burning them out, but they still won't stop
outputting light. Again, it will just keep tapering off with time.

Jeff
--
"the perennial claim that hypersonic airbreathing propulsion would
magically make space launch cheaper is nonsense -- LOX is much cheaper
than advanced airbreathing engines, and so are the tanks to put it in
and the extra thrust to carry it." - Henry Spencer