Eastern Electrical Engineering Co.

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Introduction

LED lighting in the home is becoming more popular due to the energy and money saving benefits it offers over traditional halogen lighting. One of the most common problems that an electrician faces when installing LED’s is enabling them to dim.

Resistive Dimming

Resistive dimming has become a standard way of dimming halogen lighting and it works by reducing the voltage allowed to the bulb with a variable resistor.

A resistive dimmer switch is easy to install because it is simply wired between the mains (240V) power and the bulb, however whilst the lighting is dimmed the voltage resistance is converted to heat and is not considered energy efficient.

LED’s use between 12V to 48V so a transformer is required to convert mains power (110V-240V) to the required reduced voltage. Using a resistive dimmer between the main voltage and the transformer will damage the transformer and using a resistive dimmer between the transformer and the LED will cause it to flicker instead of dimming.
Note: LED’s cannot be dimmed using resistive dimming; it will slowly damage the LED’s.

Pulse-Width Modulation Dimming

Pulse-width modulation works by switching the voltage on and off at a variable speed. This causes a flickering effect that is too quick for the human eye to see. By increasing and decreasing the switching speed it increases and decreases the max possible light output and dims the LED.

PWM dimming is energy efficient because unlike the resistive dimming the more the LED is dimmed the less wattage it uses.
A problem found with PWM dimming is as the amount of dimming increases so does the amount of time the voltage is turned off. This will eventually fall within the flickering speed in which the human eye can see.

This flickering can normally be seen when the LED is dimmed to below 10% of its original light output.