Apr 242014
 

As we enter into a new generation of lighting: Solid State; commonly known as LEDs, we need to be aware of the issues that drive the technology and hence the cost. LEDs Magazine has an article on LED Driver Design in their April/May 2014 issue. One of the issues that everyone hates is flicker.  In Fluorescent lamps, this was caused by poor ballast design or bad sockets. With LEDs, the driver operates off of line voltage with its 60hz cycle, which can cause a 120 hz flicker.

Flicker Index by Light Source*

Source Max. Min. Avg. Flicker (%) Flicker Index
Incandescent 12.2 10.7 11.5 06.3 0.0194
100W metal halide 09.1 03.2 06.5 48.1 0.1398
T12 magnetic 09.6 04.6 07.2 35.1 0.0897
T5HO electronic 10.5 10.0 10.2 02.7 0.0036
LED on DC 43.4 41.0 42.2 02.8 0.0037
LED with flicker 16.0 0.06 06.3 99.3 0.4498

*Percent flicker is a relative measure of the cyclic variation in output of a light source (modulation index). The percent flicker is based on the maximum (A) and minimum (B) light output levels. You divide the sum of A and B by the difference of the two to obtain a percentage.

There are a couple possible solutions, and this article by Zhaoqi Mao, Lane Ge, and Gary Hua of Inventronics (Hangzhou) Co. describe them in detail.

  • Passive or valley-fill Power Factor Correction (PFC) stage plus a DC/DC-converter stage.
  • Single-stage Active PFC driver architecture
  • Active PFC stage plus a DC/DC-converter stage
  • Active PFC driver architecture plus a Ripple Suppressor

The take away is you get what you pay for, the buyer of LED lamps whether at the retail or wholesale level should be aware there trade offs in Driver Design. Just buying or stocking the cheapest LED lamp or systems is a good way to be disappointed.

“As the LED lighting industry develops, features like high efficiency and long life alone cannot satisfy the market. People are looking for a better lighting environment, especially when it is related to health. For certain places like offices and living rooms, elimination of strobe flicker is even more important.
There are multiple ways to create good DC current with low ripple to drive LEDs; each method has advantages and drawbacks. The key advantage of the ripple suppressor is that it provides a very simple and flexible way to reduce the flicker of the design we already have at a minimal and very reasonable cost.”