Won't 4 hours, or even 30 minutes, be a bit long to show the bytes changing?
Don't get the wrong end of the stick, mate. The half-life is only (I'd estimate off the top of my head) 1 minute (the dynamic range of the human eye is HUGE). Ignore the fact that the eye can detect a state retained for 4-hours in a little bit of plastic.
My sensor can do a MUCH better job on a MUCH SHORTER time scale (tens or hundreds of milliseconds). I know this for a fact, I can see the frequency of the PWM output change smoothly and rather quickly in real time on my scope.
Consider the size of the wheel... 40 bits. AND it takes time to charge up each bit as well! We have time to burn!
People are apparently neglecting the other variables we have under our control:
*Charge time -- arbitrary down to the microsecond.
*Charge intensity -- a UV LED running at 30 mA.
By definition, the brightness change will be most easily detectable when the brightness
gradient is (falling) steepest. That is immediately after charging!
If my eye can see a state held for 4 hours, then a closely-coupled sensor should be able to do the same after 1 minute or however long the wheel takes to turn (less than that)!
Maybe I can read a bit, advance the wheel and charge a bit and advance the wheel again in less than 1 second. That's 40-ish seconds per revolution, without data loss. In a fairly dark room I suppose.