Dimming LED Lighting

Dimming LED bulbs is a little bit more complicated than dimming traditional light sources such as incandescent bulbs. There are many factors including the type of LED driver used and the number of LED bulbs on a dimmer switch that play a role in determining whether or not your lights will dim to your satisfaction. Several of the larger LED bulb manufacturers are now testing their products to ensure they will dim to advertised levels with a number of easily found dimmers. Conversely, several manufacturers of dimmers, most notably Lutron, are testing new LED products with their dimmers and providing the compatibility results on their websites along with other useful information for those seeking a more in-depth look at the subject. We’ll look briefly at some of the issues you may encounter and the questions you may have before providing some additional resources at the bottom of this article.

Factors That Can Effect LED Dimming:

Is the LED bulb/fixture you bought dimmable?

Not all LED lighting is designed to be dimmable, and using a non-dimmable bulb with a dimmer switch can cause the bulb to not work properly or fail completely. Furthermore, using a non-dimmable bulb on a dimmer switch can void the product warranty. Therefore, it’s important to make sure that if you plan on dimming your lights you buy LED bulbs that are designed to be dimmed.

Type of dimmer and number of LED bulbs on the switch.

Many LED products are designed to be used with standard incandescent dimmers. These dimmers work by opening the circuit during the first half of each alternating current cycle and closing during the second half. You’ll sometimes hear this type of dimmer referred to as a forward phase dimmer or leading-edge control. If you already have one of these dimmers installed, or are planning on buying one to use with your new LED lights, then you should be aware that the number of LED lights on the switch can play a role in the quality of dimming. Most incandescent dimmers have a minimum load required to operate properly that ranges from 20-45 watts. While this is easily met using just one incandescent bulb, it may require a number of LED bulbs to reach the minimum load required. If you fall below the minimum load required by a standard incandescent dimmer then you may be able to use a magnetic low voltage (MLV) dimmer to accomplish your goals. This is another type of leading edge dimmer that is typically used for controlling low voltage LED lighting systems with a magnetic transformer, but may also work well for certain line voltage LED lighting products.

Another type of dimmer, the trailing-edge (or reverse phase) dimmer is sometimes specified for use with LED fixtures. These types of dimmers function exactly opposite of a leading-edge dimmer, cutting the last half of the cycle, and are typically designed to work with electronic low voltage (ELV) light sources. Some LED drivers in light fixtures are also designed for use with this type of dimmer. Trailing-edge dimmers have the same minimum load requirements as leading-edge dimmers.

What is the dimming range of the LED bulb/fixture?

While most incandescent bulbs will smoothly and continuously dim to 1%, the same can’t be said for all LED bulbs. Many times you’ll see a dimming range specified for an LED bulb where the low end of the dimming range falls between 5-20%. LED lights can ‘drop-out,’ meaning that the light turns off before the dimmer control reaches the bottom of its travel. This occurs when the dimmer’s lowest voltage setting is lower than the voltage required to operate the light and it creates a section on the dimmer slide that is essentially dead. The opposite occurs when turning on the lights, in that the dimmer switch must be moved some distance before the lights ‘pop-on.’ Many new dimmers solve this problem with a low end trim adjustment that allows the bottom range of the dimmer control to be set at the level where the LED lights turn off.

Troubleshooting:

It can be hard to diagnose a dimming problem due to the number of variables involved. These include the type, length and age of the wiring, the number of lights, type of lights and type of dimmer. Although some lights are being tested by LED lighting manufacturers and dimming control manufacturers, there will still be a number of products that state they’re dimmable but don’t have any other specifics listed. If you experience problems such as humming lights, flickering at different dimming levels or a dimming range that falls short of manufacturer’s claims then your best bet may be to try a different type or brand of dimmer. Referring to spec sheets or calling the manufacturer of the lights, or the dimmer, may also provide the answers you need. When available, Polar-Ray.com provides easy access to manufacturer’s spec sheets and other useful information on each product page in a section titled ‘Downloads,’ located just underneath the product images and ‘Add to Cart’ button. Clicking on these links will open up a downloadable PDF file with additional details about the product.

Resources:

Lutron, one of the largest dimmer manufacturers, provides a number of LED dimming resources on their website including a LED dimmer product finder, educational materials, and a LED specific toll free number for information about using Lutron dimmer controls with LED lighting. Visit their website at www.lutron.com. Their toll free number, 1-877-DIM-LED8, is available Monday through Friday from 7AM-7PM EST.