NICOR White Paper Flicker: Common Causes and How to Avoid It NICOR, Inc. 2200 Midtown Place NE Albuquerque, NM 87113 800.821.6283 www.nicorlighting.com By Mike Garcia 11/05/2014
Figure 1: Demonstrating Stroboscopic Effect by rapidly moving an object under two light sources with different % Flicker. The light source on the left is the Nicor DLR56 with a %Flicker of 18.9% and the light source on the right is an AC driven LED circuit with a %Flicker of 99%. INTRODUCTION Lighting is an important part of our lives. For billions of years the sun has provided a constant light source that life on earth has adapted to, which is why it is important to us as humans to have a light source that does not waver in its intensity. With each new lighting technology there are many obstacles to overcome. Flicker has been a long standing issue because our power is transmitted at a frequency of 50Hz or 60Hz depending on your geographic location. Since there is no industry standard to specify the amount of flicker that is acceptable we will discuss a few different metrics in order to quantify flicker; % Flicker and Flicker Index. In spite of the lack of flicker acceptability standards, it is important to purchase lights with a low % Flicker to ensure the highest quality of light. Flicker can have health impacts and cause certain people to feel uneasy when subjected to it. What is Flicker and Stroboscopic Effect: Flicker, shimmer, and strobe are some common terms used to refer to what we call flicker. Flicker is a variation of light intensity over time commonly caused by artificial light sources such as incandescent, fluorescent, and LEDs. Stroboscopic Effect can be easily seen by observing objects in motion under a light source. An object in motion observed under a light source with no flicker will appear blurry, an object observed under a light source with flicker will appear multiple times as seen in Figure 1. 2
Health Impact: Research has shown that flicker above 100Hz can generally not be noticed, but stroboscopic effects can be perceived up to 500Hz. Flicker has been known to cause symptoms such as headaches, migraines, eye strain, distraction, and in frequencies between 3Hz and 70Hz, epileptic seizures. Figure 2: Example of how to calculate % Flicker and Flicker Index Flicker Index: 0.04 Percent Flicker: 13.4 Figure 3: Flicker from an A19 style Incandescent light bulb. Quantifying Flicker: There are several ways to mathematically describe flicker, and although we have a great scientific understanding of it, Figure 4: Flicker from a Quad Tube style Magnetically-ballasted CFL light bulb Flicker Index: 0.11 Percent Flicker: 37.0 there is no standard set for acceptable amounts of it due to its subjective nature. The most popular method is defined by the Illuminating Engineering Society (IES) in the RP-16-10 standard, where the percentage of flicker is calculated by difference of maximum and minimum amplitude divided by the sum of maximum and minimum as seen in the equations in Figure 2. The flicker index is calculated by dividing the area above the average light output by the sum of the area above and below the average light output. Both methods are illustrated in Figure 2. Flicker Index: 0.01 Percent Flicker: 5.1 Figure 5: Flicker from an A19 style Electronicallyballasted CFL light bulb Flicker in Various Light Sources: Nearly every light source driven from line voltage has some level of flicker, Figures 3-7 demonstrate the intensity and frequency of various light sources and their correlating Flicker Index and Percent Flicker as obtained from the Department of Energy. Figures 6 and 7 demonstrate the differences in flicker between the same types of bulbs manufactured by different companies. Flicker Index: 0.20 Percent Flicker: 93.2 Figure 7: Flicker from a different R30 style LED light bulb Brand B. Flicker Index: 0.06 Percent Flicker: 22.7 Figure 6: Flicker from a R30 style LED light bulb Brand A. 3
As seen in these examples, flicker can be over 90% and still be acceptable in the marketplace. In certain applications, such as outdoor lighting, a higher amount of flicker can be acceptable. In settings such as offices and schools, flicker is much less acceptable because of the associated negative side effects. Figure 8: Flicker from Nicor DLR56 Flicker Index:.062 Percent Flicker: 18.9 Figure 9: Flicker from Nicor DLS56 Flicker Index:.029 Percent Flicker: 10 Figures 8-10 illustrate data taken on various Nicor LED products. When comparing the Nicor LED products in Figures 8-10 to the LED light sources in Figures 6 and 7 it can clearly be seen that there is substantially less flicker. To better understand the comparison you can refer to Figure 1, the image on the left is light from the Nicor LED DLR 56, the image on the right is a light source with a flicker index similar to Figure 7. Flicker Index:.059 Percent Flicker: 19 Figure 10: Flicker from Nicor DEB 56 Dimming and Flicker: There are several methods used to dim LED light sources, among the most popular being TRIAC dimming, generally found in residential settings, and 0-10V dimming, generally found in commercial settings. Each type of dimmer has pros and cons when it comes to flicker. Dimming with 0-10V tends to have less flicker, but is more costly because the luminaires have extra internal circuitry and require extra wire to be run for control. TRIAC dimmers on the other hand are less expensive, but need to be matched with compatible luminaires to ensure there is minimal flicker at every dimmed level. TRIAC dimmers are the most common type of dimmers found in residential lighting and operate by cutting the leading edge of the line voltage as seen in Figure 12. Flicker tends to happen at the lower end of dimming because more of the line voltage is cut out as seen in Figure 13. Sometimes the abrupt leading edges from the TRIAC dimmer cause current spikes across the LEDs creating variations in the light output. Figure 11: Line voltage as seen before TRIAC dimming. Figure 12: Line voltage being chopped in half by TRIAC dimmer circuit. Figure 13: Line voltage being chopped to a minimum by TRIAC dimmer circuit 4
When a dimmer is not compatible with a luminaire you can see a slow flicker as illustrated in Figure 14. The flicker in Figure 14 is shining approximately 60% brighter at a frequency of approximately 1Hz. LED compatible dimmers have a knob to trim up the low end so that the end user can eliminate flicker and set the minimum dimmable level. Mitigation: When using TRIAC dimmers it is extremely important that the dimmer and luminaire are matched by the recommendation of the manufacturers. Energy Star states that each luminaire is required to have a minimum of 3 compatible dimmers. Not following the manufacturer s dimmer recommendation can often cause flicker and other maladies such as drop out and strobing. Flicker and drop out can also be minimized by wiring several luminaires to a single TRIAC dimmer. Flicker may remain an issue until a new technology is more widely used than TRIAC dimmers, luminaire and dimmer manufacturers work together to help eliminate such issues or a new technology is developed to handle the multitude of TRIAC dimmers available on the market. Summary: Due to the adverse side effects from flicker that some people experience it is important for the consumer to purchase LED products with minimal flicker and use dimmers from the manufacturers recommended list. When purchasing LED products it is important to understand that standards have not been set for the amount of acceptable flicker and further research may need to be done by the consumer to find out how much flicker a product has. Nicor LED products go through a battery of dimmer and flicker tests to ensure that they work with the largest variety of dimmers possible. Flicker data is taken on each product so there is no doubt the amount of flicker is acceptable by Nicor standards, providing some of the highest quality light in the industry. Figure 14: Flicker from a dimmed light source at a frequency of approximately 1Hz References: http://www.lrc.rpi.edu/programs/solidstate/ assist/pdf/ar-flicker.pdf http://grouper.ieee.org/groups/1789/ FlickerTR1_2_26_10.pdf http://apps1.eere.energy.gov/buildings/ publications/pdfs/ssl/flicker_fact-sheet.pdf 5