Mike... Maybe I didn't explain it well. Lee pot coils are either full on or full off. There is a thermostat connected to the heat knob. When it reaches a certain temp in the housing, (ever noticed that the crucible on a plastic pot touches the housing and on a lead pot it doesn't) the contacts open, stopping current to the coil, when it cools sufficently (depending on where the knob is set) to close the contacts, full power is again sent to the coils. The light is wired in the lead between the thermostat and the element. Using the light. I can tell if my pot is heating or not when I get to about the correct temp. As the plastic cools, I can also turn the knob until the light just comes on (heating) instead of guessing how much to rotate the switch. I never run the knob on max temp and the light just lets me know if I'm heating or not.
Another interesting think I learned from the Lee guys a while back. The plastic pots actually use a 220v element running on 110v to keep it cool enough for plastic (along with modding the open / close temp of the t/stat)