LED lighting products have many advantages that traditional lighting products can't match, and of course have their inherent shortcomings or controversies. Among them, strobe is one of the important controversies. In this paper, through the measurement and analysis of the luminous flux of various traditional lighting and LED lighting products, it gives indirect conclusions on whether there is stroboscopic and stroboscopic degree. Make some suggestions for the design and use of the product.

First, the basic concept of stroboscopic and flashing and the significance of luminescence stability

The strobe of LED lighting products has become the second major concern after the blue light hazard dispute (a lot of doubts in the early days, and the consensus has been reached through industry efforts). For the LED lighting whether there is stroboscopic, which circuit structure principle exists or how, and compared with traditional lighting, there is no experimental analysis report of the system.

Some people use digital cameras and mobile phones to take pictures or video on LED lighting products and find interference stripes. Some people use stroboscopic flashing to find stroboscopic light, so that LED lighting products are highly characterized as stroboscopic and unsuitable. General lighting. However, have these experiments thoroughly analyzed the refresh rate of digital cameras? What is the speed of the strobe? And these parameters are the key parameters to determine if someone can feel the strobe?

The stripes captured by the digital camera may be the high-frequency "beat frequency" strobe of the digital camera's high refresh rate and illumination light. This high-frequency strobe may not be felt by the human eye, that is, for people, there is no strobe. . In the same way, the problem of the speed of the screw can also be the same. Therefore, through other experiments, the problem is deeply analyzed, people's doubts are lifted, and the healthy development of LED lighting is promoted, which has great practical significance for promoting lighting energy conservation and emission reduction.

1. The concept and principle of strobe and flicker

(1) Flicker generally refers to a single flash of light or multiple flashes of time irregularity, and stroboscopic generally refers to a light repeat with regular repeatability at time intervals. Any regular repeatability of light changes produces stroboscopic, and is divided into low-frequency strobes that humans can perceive and high-frequency strobes that are not perceived by humans. Critical strobe is closely related to the "visual persistence" effect time of the human eye. It varies from person to person, and the same person may be different at different ages, circumstances, and periods.

When the human eye observes the scene, the light signal is transmitted to the brain nerve, which takes a short time. After the end of the light, the previous scene will not disappear immediately. This phenomenon is called "visual persistence". According to reports, "when the object moves fast, when the human eye sees the image of the object disappears, the human eye can still retain the image of the object for 0.1 to 0.4 seconds; for medium-bright light stimulation, the 'visual persistence' time is about 0.05. ~0.2S". Without this effect, the human eye will see the light that is constantly changing and changing, which is very detrimental to physical and mental health. ”

"Vision persistence" greatly reduces the sensitivity of the human eye to strobe. For example, the movie picture that people see is comfortable and continuous. This is because the current movie is 24 images per second (the interval between the two paintings is 0.042 seconds, which is shorter than the "visual persistence" time of most people). If the human eye does not have a "suspension effect", even if the scene is still landscape, we will see 24 pictures flashing every second, and watching for a certain period of time will cause headaches.

Second, if the time interval of the picture change is longer than the "visual persistence" time, for example, the early movie is 8 frames per second (the interval between the two paintings is 0.125 seconds, which is longer than the "visual persistence" time of some people), then The brightness of the previous painting in the brain is declining. When the "visual persistence" time is retained, it will drop to a certain extent (that is, it is completely disappeared), and the second painting immediately after it has not yet arrived. At this time, it is "dark" in the brain or in the eyes, that is, from "bright" to "dark"; when the brightness of the second picture comes, it changes from "dark" to "bright"; the whole process is constantly " Light-dark-bright flashing.

Third, strobe is also related to the speed of motion of the object. In a movie with 8 frames per second, even at a slow speed such as walking, some people appear to be beating and discontinuous pictures, and the result is equivalent to stroboscopic. For the current 24 pictures per second, the walking speed has gradually changed, but if it is a very fast moving person or thing, the content of the second image will be very different from the previous one. A more serious strobe occurred. Therefore, some TVs, computer monitors, etc., which have long-term use of eyes, have adopted a higher refresh rate of 85 Hz or 100 Hz, etc., so that the display is stable.

People don't consciously watch the light from the lamp directly. Strobe, flicker or fluctuation is the phenomenon that people observe the change in brightness on the surface of the object illuminated by the lamp. The light parameters of the lamp itself, such as luminous flux, brightness, wave depth, etc. are just Its indirectly related parameters.

According to the theory, there is absolutely no stroboscopic light that is stable DC operation. According to the experience of the predecessors, the depth of light fluctuation (that is, the ratio of the amplitude to the valley and then the amplitude) does not exceed 5% is "absolute" without stroboscopic. The fluctuation depth of incandescent lamps is about 20% to 25%. Most people feel that there is no stroboscopic, but it is not "absolute" without stroboscopic. Although many ordinary electric light sources (lights) use more fluctuating depth than normal incandescent lamps, some reach 60% to 70% or even 100%.

However, purely according to the current waveform, the equal-amplitude sinusoidal current waveform of the high-frequency electronic ballast fluorescent lamp of 20-50 KHz is the same as the fluctuation of the 50-Hz current waveform of the approximate square wave of the inductive ballasted fluorescent lamp, but people feel high frequency. Fluorescent light output is very stable, even considered to be "absolute" without stroboscopic, which is the afterglow time of rare earth energy-saving lamps is much longer than the high-frequency light wave period, which is caused by the smooth light wave....... For details, see the sixth issue of Semiconductor Lighting .

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