RE: filmscanners: LED Illumination for Film Scanners

[Julian Robinson <julian@austarmetro.com.au>]

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

>My guess is you are not an electrical engineer, or you would know that LEDs
>do have a life span.  Because you haven't heard of them burning out, doesn't
>mean they don't burn out.  In fact, their typical MTBF is rated for 1000
>hours.

I am another engineer(!) (not that this is relevant to reading a 
manufacturer's spec) and LEDs don't have MTBFs of 1000 hours!  One of the 
great advantages of using LEDs in a scanner is the enormous lifespan of the 
light source... this was also the original driver for the mooted LED 
enlarger lamp that you have been discussing -  lifespan *and* the 
consistency of light i.e. unchanging spectral characteristics.   In fact 
the MTBF of ordinary boring nothing special LEDs is around 100x  your 
stated figure and good ones (presumably like those used in scanners) are 
1000x.  I quote from the first google-located site I found...

"If packaged properly, LEDs emit light for a much longer time period than 
almost every other alternative light source technology. ... The mean time 
between failure (MTBF) of high quality LEDs properly packaged, is on the 
order of millions of hours. "


Or this second site I found...

"The long term dependability of Precision Optical Performance AlInGaP
LED lamps is an important consideration for those who specify LED
traffic signals and LED variable message signs (VMS). Precision Optical
Performance LED Lamps are T-1 3 /4 plastic package devices that
exhibit a nominal Mean Time Between (possible catastrophic) Failure,
MTBF, greater than 1.2 million hours at the operating temperature of
+74°C (+165°F). At operating temperatures below 0°C (32°F), MTBF is
in excess of 10 million hours. Therefore, MTBF need not be a concern."

Let's say the first LED dies in my scanner after 1/10 th of its MTBF, then 
I'll get 100,000 hours out of it or  50 years if I use the scanner 5 hours 
a day. Not bad eh!  (Caveat - this was an example only - I don't know what 
the figure is for the actual LEDs used in Nikon scanners, but I am sure it 
is a lot higher than 1000hours).

Julian


Julian Robinson
in usually sunny, smog free Canberra, Australia