On LED Dimmability

LED lighting has a number of strong economic and environmental advantages, but if there could be said to be a weakness of LED lighting, that weakness would be dimmability. When LED lamps first entered the market, they were pretty much undimmable. They performed very poorly and unreliably when used with existing in-wall dimmer controls. Even worse, the very way that most in-wall dimmers function to modify the input power to the LED lamp caused stress on the electronics in the LED drivers and tended to provoke premature failures. While there have been significant improvements made along the way to the current generation of LED lamps that are now on the market, LED dimmability remains somewhat tricky.

The most commonly encountered dimming control device is what is known as the TRIAC dimmer. There are estimated to be over 150 million of these installed in U.S. homes, and these are the bulk of the dimming control devices that LED lamps end up on as incandescent lamps are replaced. If you have a rotary knob or slider dimmer control nestled in among the wall switches in your home, it is almost certainly a TRIAC dimmer. Unfortunately, TRIAC dimming was designed specifically for use with incandescent light bulbs and the compatibility of LEDs with TRIAC dimmers can be problematic. The primary reason for this comes from the difference in the way that incandescent and LED lamps are powered. Incandescent lamps produce light through simple resistive loads that draw electricity directly from the AC grid. The relationship between current, voltage, and brightness is linear and straightforward. A change in the voltage affects the current proportionally. Because the LED diodes rely on drive circuitry to ensure constant current and to adapt power and voltage for their use, their interactions with TRIAC dimmers are less predictable. TRIAC in-wall dimmers don’t actually raise or lower the voltage to cause dimming of the lamps. Instead, the TRIAC dimmer flashes the power on and off at very rapid speeds, much faster than the human eye can detect, which creates the illusion of a dimming effect proportional to how much time the power is on versus how much time the power is off. Most of the early generation LED lamps were not able to properly handle this rapidly oscillating power input and would flicker or dim erratically. Even among the most current generation of LED lamps on the market, many of them still have a poor response when dimming below 50% of their normal light output, and will frequently show a very obvious flicker when attempting this low-end dimming. Furthermore, this rapidly flashing power supply, acting through electromagnetic forces, can cause the components within the LED lamp bulb to physically vibrate which yields an audible buzzing noise. Even the best LED lamps on the market, which are smoothly and evenly dimmable when used on an in-wall dimmer, will frequently produce a buzzing sound when dimmed. This phenomenon is certainly not unique to just LED bulbs. In-wall dimmers can induce a vibration in the tungsten filament of a standard incandescent bulb which also yields a buzzing noise from the light bulb that is easily heard in a quiet room.

Truly the most effective, reliable, and trouble-free LED dimming comes from the so-called “Smart Bulbs” that have entered the marketplace in the last few years. These are lamps such as the Insteon LED, the Philips Hue, and the Connected by TCP series. These LED lamps have the dimming logic and control built right into the lamp itself. These smart bulbs can be controlled with stand-alone Bluetooth remotes, or using wireless Ethernet networking, can be controlled by a home automation system using a PC or smart phone app. Many of these smart bulbs also feature the ability to change the light color along with color shifting effects. While these smart bulbs are definitely a premium product which commands a premium price, they are without question the very best LED products at dimming. They all will dim smoothly and evenly across the entire range with absolutely no flicker or audible buzz. Thus for applications where smooth low-end dimming is the most important factor, the best course of action right now is to eliminate any existing in-wall dimmers and install one of these self-controlled smart bulb systems.