LEDs dim differently than legacy lighting types which is why dimming needs to be carefully taken into account when planning an LED retrofit.
Take incandescent bulbs for example…they produce light by making a filament wire so hot that it glows. To make it dim, simply provide less voltage and the wire cools off, supplying less light. This is an example of analog dimming as you can dim from 0-100% by adjusting the voltage to the light source.
LED bulbs create light from a diode, not a heated filament. A diode only has two states: it is either ON and producing light or OFF and, you guessed it…dark.
This is why dimming LEDs is a bit different as we have to find a different way to produce a dimmable LED lighting product. There are two main methods of dimming LEDs: Pulse Width Modulation (PWM) and analog dimming.
Pulse Width Modulation (PWM)
PPWM offers a full range of dimming by varying how much time the signal is ON or OFF. With PWM dimming the light-emitting-diode can only be ON or OFF at any given time. This is different from analog dimming as analog dimming varies the output power to dim LEDs.
With pulse width modulation, if you wanted to dim an LED to 80% brightness, then you would keep the LED on for 80% of the time and off for the other 20%. This makes sense that you would have about 80% the light output , but how do we not notice the LED switching on and off?
PWM dimming exploits a problem with our vision. The light is flickering at such a high rate that the human eye cannot see it, the human eye can see from about 50-90Hz (about 60 frames per second). When the light is flashing at such a fast rate our brains fill in the gaps to make our vision feel smooth.
Be careful with PWM dimming especially if you are using the lighting in film or videography. Human’s vision may not catch the PWM flickering but a high quality camera will definitely pick up a slight strobe when the light is on a dim setting. You should look for a better dimming option than PWM when working in videography.
