The Science of Dimmability in Energy Efficient Home Lighting

1. The basics

In the brilliant move from incandescent lighting to more energy efficient alternatives, one of the biggest hurdles has been the issue of dimmability. We all love dimming lights, for the obvious reasons (think Marty Robbins: "Turn the lights down low, let your feelins go"). But, until recently, it was simply impossible to find high quality, dimmable, energy efficient lighting.

The cold, hard truth is that the average compact fluorescent light (CFL) bulb you can pick up at the grocery store doesn't dim. And despite manufacturer claims to the contrary, even dimmable CFL bulbs and dimmable LED bulbs won't work well with just any dimmer. We realize that there's nothing more frustrating than being told something works, and then it doesn't. So we thought you'd appreciate knowing what to look for—so you'll be delighted with your new dimmable energy efficient lighting when it arrives.

2. How manufacturers are making dimmable energy efficient lighting today

Dimming CFLs and LEDs has been problematic because of the way they work. So to understand the problem of dimmability, it helps to understand what goes on inside CFLs and LEDs. Here's a brief rundown of the science:

• When you flick a switch to turn on a CFL, the bulb's ballast sends an electrical charge into the bulb's cathode, heating it up.
• That heat causes it to emit electrons, which then scatter throughout the mercury within the glass tube and collide with the mercury atoms.
• This collision releases UV light, which then reacts with the phosphor coating that lines the glass, creating visible light.
• If you reduce the current in a dimmable CFL too much, the cathode doesn't doesn't get hot enough to emit electrons.
• LEDs, similarly, won't function properly if the current is increased or decreased beyond certain parameters. LEDs also rely on electrons moving between a cathode and an anode; if the current is reduced too much, the bulb will flicker or go out.

Manufacturers of lighting and dimming systems have been tackling the issue in a couple ways. Some lighting manufacturers have created ballasts that, when used with the right dimmer, send enough current to the cathode to keep it hot. At the same time, these ballasts reduce the amount of current that actually runs into the lamp.

Manufacturers of dimmers are now designing dimmers to be explicitly compatible with energy efficient lighting, which they do by adjusting the maximum and minimum current delivered to the bulb. That way, they match the parameters within which the bulb will function; they'll also adjust the dimming curve to match the lighting they're dimming.

3. Choosing the best lighting + dimmer

Since the electronics vary between bulb make and model, we've found that the best performing dimmer/bulb combinations are those specifically designed for each other (the Leviton Programmable SureSlide Wall Switch Dimmer, for example, was designed to the exact electrical specifications of the Philips R30 Dimmable Marathon Flood CFL). On the other hand, many dimmers on the market today are designed to roughly correspond with a wide range of CFLs. And while these may roughly work with most dimmable CFLs, you probably won't get the same results as you would with a dimmer/bulb combo designed to work together.

The same holds for LEDs: Non-dimmable LEDs shouldn't be hooked up to dimmers, and we've found that dimmable modules like the Cree LR6 downlight work best with certain dimmers. As with dimmable CFLs, dimmer manufacturers are now making dimmers to the specs of a particular LED bulb. Case in point: Lutron has designed the Skylark LED dimmer for use with the Cree LR6. (It's also worth noting that if are only one or two LEDs on a circuit, the total wattage is so low that you'll get the best results with a low voltage dimmer.)

Dimmer/light combinations that aren't specifically designed for each other can be hit-or-miss. To reduce the "misses," some manufacturers have tested their lights with a number of different dimmers to see which ones work the best. (Lutron has a very handy product compatibility matrix that lists which LED light fixtures play well with their dimmers.)

4. Multi-location dimming

Got it? The final frontier is a question we get a lot: "Do dimmable energy efficient lights and energy saving dimmers work in three-way and multi-location installations?"

The answer: Yes.

But you must buy a dimmer that's compatible with multi-location installations. Rather than a sliding dimmer, many of these will often have "up" and "down" buttons beside the switch. That way, multiple dimmers can "talk" to each other digitally, which eliminates the problem of eight different dimmer switches all set to different romantic moods.

Other dimmers, sporting the beloved up-down slide feature, can work well in conjunction with a regular switch at another location. These can be a great option for typical multi-location situations, such as a hallway, where there are two often-used switches. Just be sure that if you install a dimmer in one of these locations, you get in the habit of turning the light all the way off rather than just dimming the light all the way down. If the light is dimmed down on one side of the hallway, and you flick the switch "on" on the other end, the light won't turn on. And we wouldn't want you to trip, for goodness sake.