Controlling LEDs Part 7 - What is the dimming performance of the product?

Each manufacturer defines dimming in a different way, but what you need to know is whether the dimming will be distracting or have noticeable, unexpected drops in light. The public’s experience with incandescent dimming is that it is smooth and continuous. Specifically, a change in the control (dimmer) position should be reflected by an equal change in light level. There should be no abrupt change in light level as the light source is being dimmed. 

Even more important is ensuring that there are no points of flicker in the dimming range. Flicker is the unexpected modulation of light level that is visible to the human eye. Flicker can come from many sources, including line noise, control noise, component tolerance, and LED driver circuit design. Flicker can be continuous (happening all of the time), or intermittent (only happening some of the time or at certain light levels). A good driver should account for all of these factors and still provide flicker-free, smooth, and continuous dimming.

Other undesired behavior can occur when dimming an LED. A properly designed driver should not have any of the following problems:

• Pop-on: After being dimmed to a low light level and switched off, sometimes LED bulbs will not turn on until the dimmer’s slider is moved up. This is referred to as “pop-on,” which is especially challenging in 3-way situations where lights can be turned on/off from different locations, not just using the dimmer.
• Drop-out: There should be no drop-out, so the light should only turn off when the switch is turned off. This can be achieved by utilizing the low end trim settings available on many wallbox and system level dimmers to ensure that the lights remain on at their lowest light level at the bottom of the dimmer’s travel.
• Dead-travel: Adjusting the control without a corresponding change in light level is undesirable
• Audible Noise: Buzzing from the lamp, or from the dimmer due to the lamp.
• Shimmer: Small changes in light intensity. This can usually only be noticed at medium to low light levels, and often only at the periphery of vision.