James - You wrote:
>
>Hi Wayne,
>        How would I obtain this information ? Manufacturer or trial and
>error ?
If the manufacturer does not publish a "Percent Change of Light Output vs Time"
 you
could estimate it for the generic type (GaAs is better than GaAlAs) and use
 other
manufacturer's specs. Otherwise test aging yourself with a linear photodector.
 Also
remember temperature is major factor in LED light output (-0.5% per degree
 typical).

>As far as time goes, the counters would only be underwater for 12 to
>18 hours at
>the most. But a concern would be that the display stopped working
>while down below.
>If a return trip had to be made because the display was out it could
>get very costly in a hurry
>at multiple thousands of dollars per hour.
>        I just returned from looking at your web page.. I would sure like to
>pick your brain about
>the next project. A 2 axis inclinometer that will send RS232 up to
>the surface. I was thinking of
>using the PIC 12C671 with it's built in A/D converters and 2 pins
>left for RS232.
>        Thanks for taking the time to reply to my post.
>        James Holbrook
>
>On Saturday, February 28, 1998 8:21 AM, Wayne Foletta
>[SMTP:foletta@IX.NETCOM.COM] wrote:
>> Be sure to check the "half-life" spec of the LEDs versus forward
>> current for the LEDs you are using. With some brands of LEDs the
>> light output falls off very quickly at higher currents (over 20%
>per
>> decade of time at 2X rated maximum If).
>>
>> Wayne Foletta
>> Data Acquisition Engineering
>> SiliconSoft, Inc.
>> http://www.siliconsoft.com
>