Facing the problem of LED lighting strobe

In the 2014 LFI Lighting Exhibition, the solid-state lighting training seminar hosted by the US Energy Administration, one of the lessons was "Understanding LED Strobe and Why Should We Pay Attention to This Issue" (Michael Poplawski and Naomi Miller, 2014), which reopened the industry’s focus on lighting frequency. Flash discussion. This topic was first proposed by the Solid State Lighting System and Technology Alliance in the United States. It studied people’s tolerance for lighting strobe and published it in the LED professional magazine (Rebekah Mullaney, 2011). It is hoped that LED brands and manufacturers can re-emphasize the problem of video flicker and create more Good and more suitable for people's health lighting.

However, after 2012, the LED lighting industry experienced price-cutting competition and blood flow. No matter how large or small and medium-sized enterprises are first concerned about "how to reduce costs", how many manufacturers pay attention to the quality of lighting is worth pondering.

What is lighting strobe

Any electronic light source driven directly by AC power will produce stroboscopic due to current fluctuations. The light-emitting principle characteristics of fluorescent tubes, high-pressure sodium lamps and LED lighting are easy to quickly respond to current fluctuations, so the stroboscopic degree is relatively large. It is converted into a stable direct current input by circuit design. Generally, the mains frequency is 50~60 Hz, and the flicker frequency of fluorescent tubes after circuit conversion is a multiple of 50~60 Hz, usually 120 Hz.

We usually do not feel the flicker of the light source because the flicker frequency is very fast, nearly a hundred times per second. The naked eye can only recognize the flicker below 100 Hz. Although the flicker above 100 Hz cannot be recognized by the naked eye, it can be detected by the stroboscopic effect.

The effect of stroboscopic on the human body

According to the stroboscopic instructions published by the US Department of Energy (US Department of Energy, 2013), the low-frequency flicker of the light source can trigger epileptic seizures. The office environment uses fluorescent tubes with inductive ballasts. It has also been studied to be related to headaches, easy fatigue, and eyesight. People's discomforts such as blur and weakened vision are related. The stroboscopic effect may even cause the illusion when driving at night, mistakenly thinking that the moving object is stationary or slowing down; or in an industrial environment, the stroboscopic effect may cause work safety.

Facing the problem of LED lighting strobe

Light source stroboscopic light can easily cause negative effects on certain ethnic groups, including children, autistic patients, migraine patients, and epilepsy patients. Since stroboscopic cannot be directly detected, people often do not realize that stroboscopic is actually the main cause of some uncomfortable symptoms. As long as the lighting quality is improved, some fatigue symptoms can be reduced and work efficiency can be greatly improved.

Stroboscopic analysis of market lighting products

Generally, we recognize that fluorescent tubes have serious flicker problems, but we are not sure whether LED lighting has such flicker problems. The following survey by the Pacific Northwest National Laboratory (PNNL) in the United States may let you and me fall through the glasses .

PNNL surveyed 25 lighting products on the market (Figure 5). From traditional incandescent lamps, metal halide lamps, fluorescent lamps to LED lamps, the stroboscopic comparison and analysis were performed. The closer to the lower left corner, the stroboscopic status is approaching zero, and the closer to the upper right. Angle indicates that the stroboscopic condition is very serious.

Incandescent lamps, metal halide lamps, and fluorescent lamps are three types of traditional lighting. The stroboscopic condition of fluorescent lamps is more serious. However, no matter which brand of traditional lights with the same attributes, the distribution of stroboscopic conditions is very concentrated, which means that the technical standards of each brand for stroboscopic problems are similar.

However, the results of the analysis of LED lighting are very interesting. The distribution of stroboscopic conditions is unexpectedly large. Among them, the stroboscopic conditions of 4 samples are very serious, which are located in the upper right corner, which is worse than the stroboscopic conditions of traditional lighting. However, there are also 3 samples whose strobes are better than traditional lights. They are distributed in the lower left corner, indicating that there is almost no strobe.

Solve the stroboscopic problem of LED lighting

From the above market research and scientific research, it can be found that some brands can reach zero flicker, but there are also many brands with serious flicker problems. In other words, the stroboscopic problem of LED lighting is not an unsolvable technical problem, but a cost problem invested by manufacturers in the production process. Luo Xianjie, general manager of Haoran Technology, a Taiwanese LED high-power lighting manufacturer, said: "Whether we can create a high-quality LED light source with zero flicker, the key lies in whether the LED power supply is a two-level architecture circuit design. Due to price competition, many manufacturers are unwilling to spend on production. A two-stage structure circuit.” As shown in Figure 5, the input current is AC, but the LED chip operates on DC, so it must be converted through the circuit.

There are currently two circuit architectures: single-level architecture and two-level architecture. The circuit design of the single-stage architecture is simple. It only needs to convert AC to DC once. Although the cost is low, it cannot effectively suppress the DC ripple. Because the LED chip has an exponential relationship between the forward bias and the current, it is extremely fine. A small voltage change will also cause a great change in current and luminosity, which also means that the stroboscopic problem is more serious. The circuit design of the two-stage architecture converts the DC power with ripples through the filter circuit into a more stable DC power, which is then supplied to the LED chip to operate, so it can effectively suppress the ripple flicker (Figure 6), but the relative cost is relatively high. high.

The extra circuit board volume of the two-level architecture needs to be installed in the limited space of the power supply structure, testing the manufacturer's circuit design technology. In addition, the safety regulations stipulate that the power supply parts must be separated by a certain distance, which is another technical threshold to comply with the safety regulations. Manufacturers must spend a higher cost to complete the two-level architecture circuit, so the problem of improving LED lighting strobe will actually be reflected in the product cost and price.

The problem of lighting stroboscopic is never a new issue, it has existed since traditional lighting. However, in the face of new LED lighting patterns, the stroboscopic problem has resurfaced, and it may be more serious than ever. The stroboscopic situation of some LED products on the market is much more serious than that of traditional fluorescent tubes. It is unavoidable to worry about whether long-term exposure to harsh light sources will have negative effects that we do not know. Consumers are concerned about whether the price of LED bulbs has reached a sweet spot, but they do not know that some manufacturers are ignorantly pursuing market share and catering to consumers to reduce prices, but they may give up quality and health. What consumers ultimately need is price or health, which is a question worth pondering.


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