dimmer switch

Instead of diverting energy from the light bulb into a resistor, modern resistors rapidly shut the light circuit off and on to reduce the total amount of energy flowing through the circuit. The light bulb circuit is switched off many times every second.

The switching cycle is built around the fluctuation of household alternating current (AC). AC current has varying voltage polarity -- in an undulating sine wave, it fluctuates from a positive voltage to a negative voltage. To put it another way, the moving charge that makes up AC current is constantly changing direction. In the United States, it goes through one cycle (moving one way, then the other) 60 times a second. The diagram below shows this sixtieth-of-a-second cycle.

A modern dimmer switch "chops up" the sine wave. It automatically shuts the light bulb circuit off every time the current reverses direction -- that is, whenever there is zero voltage running through the circuit. This happens twice per cycle, or 120 times a second. It turns the light circuit back on when the voltage climbs back up to a certain level.

This "turn-on value" is based on the position of the dimmer switch's knob or slider. If the dimmer is turned to a brighter setting, it will switch on very quickly after cutting off. The circuit is turned on for most of the cycle, so it supplies more energy per second to the light bulb. If the dimmer is set for lower light, it will wait until later in the cycle to turn back on.

That's the basic concept, but how does the dimmer actually do all of this? In the next couple of sections, we'll look at the simple circuitry that makes it work.

When you're furnishing a home, light is everything. The light level in a room dictates what you can and can't do, and it has a huge effect on how you feel. You can't read very easily by a single candle, for example, and a romantic dinner for two isn't so romantic under a 1,500-watt halogen lamp.

How do dimmable LEDs work?

The benefits of dimmable incandescent and compact fluorescent light bulbs, that is, the ability to easily adjust the intensity of overhead lighting, improved energy efficiency, etc., are all greatly enhanced when dimmable LEDs are used instead.

Dimmable LED light bulb by Razorlux

But how, exactly, does this particular type of LED technology work? This has become a common question to ask as today’s consumer becomes more aware and thus more curious about the benefits of LED technology.


First and foremost, LEDs are not dimmed based on an increase or decrease of voltage (as is the case with their incandescent counterparts.) Light gets emitted from a semiconductor chip, so it’s either on or off, and the LED will maintain its operation at the same voltage and current level as if it were operating at full light output.

Instead, what the LED does is it creates a “dimming effect.” There are two ways to do this: pulse-width-modulation (PWM LED) and analog dimming (sans cool-sounding acronym.)

Pulse-width-modulation LEDs

With pulse-width-modulation, the LED is wirelessly programmed to split its “on” time cycles, measured in milliseconds or thousands of a second, into intervals where the light is “on” and “off.” Take a look at the chart below.

Pulse-width-modulation is one way to dim LEDs.

For a low-lit light effect of just 10% brightness, the LED is “on” 10% of the cycle and “off” for the other 90%. For an LED light dimmed to 50% brightness, the light is turned “on” for half the cycle. Basically, the longer the “on” periods are relative to the “off” periods, the brighter the LED looks.

This, of course, begs the obvious question — why doesn’t it look like the light is blinking?

PWM LEDs rely upon the human eye’s ability to assimilate the average amount of light out of the pulses. As long as the rate is high enough, the eye won’t perceive any pulsing. Instead, it’ll recognize the overall average. To ensure the flickering is not noticed, the frequency of today’s PWM LEDs range from a few hundred to hundreds of thousands of pulses per second.

Analog dimming

Analog dimming is another way to dim an LED. In this scenario, the analog dimming supply controls the forward current being fed to the LEDs; its electronics linearly reduce the current so as to dim the LEDs.

While this technique is pretty simple to implement, and the efficiency of the LED is increased when run at a lower current (dimming reduces operating temperatures inside the light source), this particular type of LED doesn’t necessarily offer the best performance. That’s because it can turn out an inconsistent color as a result of the lower drive currents. This is particularly noticeable if different colored LEDs are used in a variety setting to produce white light. The amount of shift in current, particularly with red and yellow LEDs, can end up producing a low-quality white light.

Why’s it taking so long for dimmable LEDs to catch on?

The challenge for LED manufacturers is to design an affordable LED that can be retrofitted into existing installations, with the capability of being able to work with a variety of established dimming-control technologies as well as any emerging wireless-network-control scenarios.

This is a tall order, to say the least. And while there are dimmable LEDS already available on the market, it still is a developing technology. As it continues to advance, prices will become more consumer-friendly, at which point we will likely begin to see a broader adoption of LED technology in more and more homes.

The problem is that people need to use some rooms for multiple purposes, and these different functions call for varying amounts of light. Enter the dimmer switch, a handy electrical component that lets you adjust light levels from nearly dark to fully lit by simply turning a knob or sliding a lever.

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