What is the Stroboscopic Effect?

According to the definition of JGJ / T119 "Standard for Architectural Lighting Terminology", the stroboscopic effect is that under the illumination of light with a certain frequency change, the movement of objects observed by people appears different from its actual movement. The strobe effect is caused by the flicker of the light source, and flicker is an unstable visual phenomenon caused by the light stimulus whose brightness or spectral distribution fluctuates with time.

According to the definition of JGJ / T119 "Standard for Architectural Lighting Terminology",

The technical mechanism of strobe is not only a factor of power supply, but also a factor of backward technical performance of electric light source, and an unreasonable factor of lighting design. And it is the result of the comprehensive effect of many factors, we only analyze from the perspective of the technical performance of commonly used electric light sources.

1.Low frequency of luminous body driving electric power

2.The power supply voltage of electric light source fluctuates greatly

3. Electric light source performance

Because an incandescent lamp is a heat radiant light source that directly heats and emits light, the luminous power of the luminous body must inevitably fluctuate with the frequency of the power supply. High-pressure mercury (sodium) lamp, straight tube (inductive) fluorescent lamp, although it is an electric light source for gas discharge. However, since it is started and ignited using an inductive ballast (without AC-DC-AC frequency conversion function). Therefore, the discharge power of the gas discharge luminous body must also fluctuate with the frequency fluctuation of the power supply. The impact of voltage fluctuations can be quantified using the two concepts of visual sensitivity curve and flicker voltage limit curve. The flicker of a light source that can be perceived by the human eye can be measured by a statistical method. When the flicker frequency is above 40Hz, the feeling is not sensitive; the flicker above 50Hz is completely not felt. ^[2]

1. Illumination flashes periodically: such as the flicker of AC fluorescent lamps and the flicker of light sources caused by fluctuations in power supply voltage;

2. Illumination flickers non-periodically: if the start of AC fluorescent light flickers, various faults flicker;

3. Display device flicker: flicker caused by scanning display of televisions, computers, electronic game consoles, advertising screens, etc .;

4, artistic lights flashing: such as neon lights, lanterns and laser flashes.

Although IEEE PAR1789 "The Potential Health Effects of LED Lighting Blinking" gives the "undetectable" and "low risk" limits of the depth of fluctuations and stroboscopic index, and defines the depth of fluctuations [depth of fluctuation = (AB) / (A + B ) * 100%] and stroboscopic index [flicker index = Q ₁ / (Q ₁ + Q ₂ )], but it is difficult to achieve in practical applications, mainly because it will increase the cost and volume of LED light sources.

The new GB / T 31831-2015 "Technical Requirements for LED Indoor Lighting Applications" standard uses this definition and limit. The original ENERGYSTAR lamps V1.0 draft 4 also intends to use the stroboscopic index as a limit, but it is considered difficult to achieve and was not adopted in the end.

For example, Energy Star originally stipulated that the permissible range of light source flicker is that the frequency is not less than 120Hz; in the frequency range of 20Hz-800Hz, the stroboscopic index is less than 0.001 and the frequency; when the frequency is greater than 800Hz, there is no requirement for the stroboscopic index.

The strobe of the light source has a stimulating effect on the human visual system, and will produce an uncomfortable feeling. People who work or live under flashing light for a long time may also affect the physical and mental health of the visual system. The severity of this stimulating effect or influence is related to the intensity, frequency, duration of the duration of the flashing of the light source, and long-term. This effect is often slow, so it has not attracted much attention for a long time. The strobe and stroboscopic effects of electric light sources have brought serious harm to our work and life. So what harm can strobes cause to the human eye?

1. Illusions caused by work accidents occur when the stroboscopic frequency of the electric light source is an integral multiple of the speed (rotational speed) of the moving (rotating) object. The motion (rotation) state of a moving (rotating) object will produce static vision, inversion, slow motion (rotation) speed, and the false vision of the above three states periodically repeated, causing an accident at work. For example, machine tool operators in the machining industry have the illusion that the turning tool is rotating in the reverse direction. The emergency reversing operation will damage the workpieces and tools, and even cause casualties.

2. Harm to health

Strobe effects can cause visual fatigue and migraines. Especially in the machinery industry, high-pressure mercury (sodium) lamps are used, and in light industry, food, printing, electronics, textile and other industries, straight-pipe (inductive) fluorescent lamps are widely used in lighting applications. For example, plug-in operators on the assembly line can easily cause migraines due to visual fatigue and dazzling. Difficult positioning occurs, and production efficiency is low.

3. Impaired eyesight of adolescents

In recent years, straight tube (inductive) fluorescent lamps have been widely used in homes, schools, libraries, etc. Growing students have suffered the most. According to data, many young people have shown a significant decrease in vision when reading in a strobe environment , Myopia significantly increased. ^[3]

Strobes are sometimes harmful and sometimes useful.

(1) Translation effect

Strobes can be used to prove that the luminous intensity and color of fluorescent lamps change periodically over time. We know that when the burning incense is moved quickly in the dark, the bright spot of the incense will become a bright line. Imagine that the bright spot flashes several times during the movement. This bright line will become intermittent and bright. The corresponding trajectory is At the moment of bright and dark, the corresponding trajectory will become invisible. Using this principle, it can be proved that the fluorescent lamp is flashing and flashing, and it is a flickering light source. Of course, it is difficult to move the fluorescent light quickly. We can take a small piece of white paper and quickly move it back and forth under the fluorescent light. We will see that the motion of the paper is intermittent (the effect of moving in front of the TV is more obvious) This indicates that the fluorescent lamp is a flashing light source. It is interesting that when you hold a bright object such as a silver-white pen cap and quickly move back and forth parallel to the tube under a fluorescent lamp, its brighter motion trajectory will surprise you. There is no interruption in the place of interruption, and there is still orange light connected. That is, its motion trajectory is actually a white and orange colored light band, and the white part is slightly cyan. If you use a flat mirror, you can see this colored light band more clearly. Hold the flat mirror in hand, and make it rotate quickly back and forth around a straight line parallel to the fluorescent tube, like a summer fan, but it will be very fast. You can see that the virtual image of the lamp flickers quickly behind the mirror, and the movement of the virtual image is a clearer orange and white colored light band. This proves that the color of the fluorescent light changes periodically over time.

(2) Rotation effect

Use "strobe" to measure the speed of rotating objects. As shown in the figure, a disk is shown. The surface of the disk is painted black except for the three white strips with the same shape, equal clearances, and even distribution. Driven by a continuously adjustable DC motor, the disk can rotate counterclockwise around an axis passing through the center of the circle and perpendicular to the surface of the disk. When the disc rotates rapidly, under the illumination of incandescent lamp (non-frequency flash source), a white ring with a width equal to the length of the strip will be displayed on the surface. The disk speed increases slowly from zero, then the following graphics are presented on the disk surface:

(1) 12 white strips are evenly distributed on the disk surface;

(2) 6 white strips are evenly distributed on the disk surface;

(3) 3 white strips are evenly distributed on the disk surface.

(1) High-frequency electronic rectifier (AC-DC-AC) is used, but the price is expensive;

(2) Adjust the vertical height of the light tube, and choose an appropriate distance like an ordinary CRT TV;

(3) Do not connect N lamps in parallel on one hot wire, use three-phase tapping, and try to balance three phases, such as: double tube fluorescent lamps are connected in different phase sequences;

(4) Three primary color energy-saving lamps;

(5) The installation of mixed lighting such as incandescent lamps can also reduce the impact of strobe effects on people. ^[4]