Download LED Lighting - Dimming Guide

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.
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 'dropout,' 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.