LED Lighting - Dimming Guide
Although you can find a large selection of dimmable LED light bulbs in a wide array of shapes and sizes, the dimming performance of LED bulbs can vary greatly based on the type of dimmer switch used to control the lights. While it's not overly complicated, there are several factors to consider before buying, and a little homework up front can save you from a large headache after spending the money to upgrade to LED lighting and then encountering problems. Factors such as the number of LED bulbs on the switch, both minimum and maximum, and whether the LED drivers in the bulbs require the use of special LED dimmers, standard incandescent dimmers, or the use of magnetic or electronic low voltage dimmers are important to keep in mind while shopping and trying to determine the overall cost of upgrading. Several of the larger LED bulb manufacturers are now testing their products with specific dimmers to ensure that they will dim to advertised levels without causing flickering or other issues. When the are available, you'll find these dimmer compatibility guides in the 'Downloads' section on each product's page. Just look for the red links below the main image and 'Add to Cart' button. 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.
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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.
The method for determining the maximum number of LED bulbs that can be used on a single dimmer switch differs from that used by incandescent light bulbs. With incandescent bulbs, one simply divides the maximum rated power of the dimmer by the wattage of the bulbs being used on that dimmer. For instance, a typical 600W incandescent dimmer can have up to eight 75W bulbs on a single switch (600/75=8). Using the same calculation for LED lighting would lead one to believe that up to seven times the number of LED bulbs could be placed on a single switch but, due to the inrush current or repetitive peak current of the LED bulb, the overall number of LED bulbs on a single dimmer switch is usually similar to the maximum number for incandescent lighting. Therefore, for LED light bulbs, the maximum number of bulbs used on a single dimmer switch is best determined by referring to a manufacturer's dimmer compatibility guide.
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.
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.
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.