RE: filmscanners: LED Illumination for Film Scanners

[Raphael Bustin <rafeb@channel1.com>]

On Fri, 22 Jun 2001, Julian Robinson wrote:

> Hey let's keep this clean and vaguely accurate even if it is OT...


Austin went just a bit over the edge with that 1000 
hour MTBF figure.

Having designed many circuits and systems around HP 
LED displays, optocouplers, fiberoptic transceivers, 
etc., I was troubled by that number.

HP is now Agilent.  Check out 

www.semiconductor.agilent.com

and do a quick search using the search phrase 

"LED reliability"

The first PDF I found cites a particular type 
of LED, used in highway warning signs, with 
a MTBF of 1.5 million hours (before catastrophic
failure). For simple aging, the paper cites 
100,000 hours of operation before a 25% 
reduction in light output.

A second paper gives mildly contradictory 
data.  This one (discussing LEDs for 
instrument cluster lighting) gives 10 million 
hours MTFB (catastrophic failure) and 50,000 
hours of operation before a 75% reduction in 
output.

Either way, I think most of us won't have 
to worry much about LEDs failing in our 
Nikon scanners.  The scanners will be long 
obsolete before the LEDs die.

2000 hours is roughly a year's worth of work-
days (weekdays) at 8 hours per day.

I suppose if you figure in hard mechanical 
shock (like in Austin's Land Rover) the 
numbers might go down a bit.  Time to fix 
the potholes in your driveway, Austin, 
or get new shock absorbers for that beast.



rafe b.