[Laser] PWM of LED in QST

[Tom Becker]

  Why wouldn't PWM cause flickering?  I don't get or have access to QST 
so I can't comment on the schematic (although using a 555 as a 
"modulator" intrigues me; is it using the 555 comparators to switch its 
output at the oscillator rate?), but PWM is often used to produce lower 
average currents, mimicing analog changes, by digitally switching full 
currents for variable periods.  The effective average current change 
should be visible as the modulation intensity changes, no?

Tom