ATM Brightness of LED

["Scott Berfield" <sberfield@xbox.com>]

I learned an important but small thing as I got to the end of figuring
my mirror. I was having a ton of trouble reading the Foucault test and I
couldn't figure out what was wrong. It wasn't until I tried taking a
picture of the Ronchi test and saw how dark it came out that I realized
what it was. Over the many weeks I have been doing this, the batteries
in my tester had faded to the point where the LED was app.. 1/4 as
bright as it had been. As a result, the contrast levels were so low I
could barely read the thing unless the room was totally black. Duh. the
decrease had been so gradual that I never noticed it (I just thought my
already bad eyes were getting worse. I put in new batteries and all of a
sudden the test was readable again.
 
Moral: If you are running into difficulties, don't rule out the obvious!
 
-sb