Pulse Width Modulation

Posted on January 3, 2013 Category: Lighting Terms

Pulse Width Modulation

What is Pulse Width Modulation (PWM) and when is it used?

PWM is a method of controlling power to devices. LED lights cannot accept analog signals, so PWM is a common method of dimming LED lighting. Pulses are sent to the light of on and off periods that visually even out to appear as a steady dimmed light.

How is it measured? Where can I found output PWM frequency information?

PWM frequency is measured using the oscilloscope to view the period length. Each controller is tested in our lab for accurate results. This information is posted under the “Specifications” heading for each item on our website and in the manual.

What is a good PWM?

There is no single answer to this question. It all depends on preference and the end use of the lighting. Generally speaking, the human eye does not see an appearance of flicker in lighting with PWM frequency above 60-80 hertz. If lights are separate from the eye by a diffuser or bulb the appearance of flicker is further reduced.

If that’s true, then why does EL sell controllers with such high PWM frequencies?

Cameras tend to pick up on PWM flicker at much higher frequencies than the human eye. Still shots occasionally show distortions of lighting with PWM frequency of up to several hundred hertz. Digital viewfinders may also output flicker, making it hard for the photographer to focus a shot.

Video cameras, especially those used in professional studios, can pick up on flicker at much higher frequencies than normal cameras. For this reason, EL has developed the Studio Line. All controllers in this line have either a PWM frequency of 5,000 hertz, or a scrambled PWM (see Scrambled Pulse Width Modulation) of 2,000 hertz.

What is duty cycle? Hertz?

Duty cycle refers to the percentage of the period that the light is on. As you dim the light the duty cycle (and power consumption) will decrease. At full brightness the duty cycle will be 100%. Hertz is a unit here equivalent to periods per second.

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