Dimming happens at a much faster frequency. Here in the US we have 60hz electricity which means 60 cycles per second. A cycle consists of a positive half cycle and a negative half cycle. The half wave goes for 8.3ms. The longer you delay before turning on power in the half cycle the less overall power. Thats the basics on how power is regulated. With pulse proportional the power is turned on for full cycles (full half of a cycle in our case) instead of a percentage through the cycle. Then its just a time slice type of regulation. Now most of the time when someone is trying to do a pulse proportional control they cheat and just try to use actual time but that is inconsistent because they can come in halfway through a cycle if they are not tracking the ac sinewave. But its cheap and has less components and it fools people. We actually still time our pulses with the sine waves which produces not only constant power but we can actually do much finer control. So with a herpstat pulse proportional mode is actually very close to the type of fine control and regulation that you get from dimming.
Now which one is better? In most cases dimming is still the best method of control power and only has one real disadvantage and that come with metal rack systems. When heat tape on a metal rack system is controlled with dimming mode control in some cases the frequency of the electrical is just right to where you can hear faint audible hum/ring in the metal. Since pulse proportional mode is on and off for full half wave time slices (in our products anyway) it tends to not have that same frequency problem.
Pulse proportional is no good for lights as heat souce. In fact even dimming mode thermostats in the past were never recommended for lights. Because the nature of a thermostat is to turn off power when the target temp is reached so as to not overshoot too far. You often end up with a disco light show. But recently I wrote in a option called Basking Assist and with that option we have had great positive feedback that it smooths out the regulation and now makes using lights a possibility.
Hope that info helps! We do listen and are constantly tinkering.
Dion Brewington
Owner, Spyder Robotics
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