[sdiy] Do LDRs and/or LEDs age?

[eq927 at freenet.carleton.ca]

Don't know about the LDR's... but LED's are usually quoted as having an 
expected operating life of 100,000 hours before they deteriorate to the 
half-brightness point at nominal operating current at room temp - that's 
about 20 years of non-stop operation. Higher currents will speed the 
aging process. Note that this does not mean the LED "burns out" - it 
simply is not working as efficiently as when new.

I have looked at data sheet curves for infrared LEDs operated near the 
maximum recommended current - some of these show about 5 percent 
decrease in output intensity over the first 24 hours of operation - the 
rate of decrease levels out after this. Pretty unlikely the gear has 
seen anywhere near 20 yrs of accumulated operation - but if the LEDs are 
being pushed hard by the circuit they are used in perhaps it is 
reasonable to assume that recalibration would be needed after a few 
years. By this time other components will also have aged so 
re-calibration would be needed anyway.
Regards, Mike