LED strobe causes
When assessing the influence of light source on the human eye, it is inevitable to mention stroboscopic. With the advancement of electric light source technology and the deepening of people's understanding of light biology, solving the stroboscopic problem is undoubtedly a key to achieving healthy lighting.
When people are in a lighting environment, it does not seem to be noticeable. In fact, in addition to warning-like flashing marks or lamp failures, there is not much intuitive perception of the concept of strobe. When observing the rotating fan blades, it is found that the blades are sometimes "stationary" and sometimes "rotating", and this phenomenon can also occur in the running car tires, which can be explained as the visual persistence caused by the stroboscopic light source.
In the figure below, a white point on the black disc, when the disc rotates, under the fluctuating frequency flash source, the phenomenon of graph a will appear, and the continuous change of graph b will occur under the condition of no stroboscopic illumination.
Figure a Figure b
Strobe cause
The stroboscopic light source is essentially that the light emitted by the light source exhibits a certain frequency and periodic change with time, and changes with time between different brightness and color. If the driver of the luminaire does not have suitable electronic circuits, such as ballasts, drives or power supplies, the source will strobe, the greater the fluctuation of the output luminous flux, the more severe the strobe.
The technical mechanism of stroboscopic generation has not only the factors of power supply, but also the performance factors of electric light source technology and the unreasonable factors of lighting design. For many lighting fixtures, the operating current of the light source must fluctuate with fluctuations in the input voltage, directly causing stroboscopic fluctuations in the light output.
Taking the incandescent lamp as an example, the driving is 50 Hz AC mains, and the light flickering frequency is 100 Hz after the negative half cycle and the positive half cycle are superimposed; the gas discharge lamp using the inductive ballast also fluctuates with the fluctuation of the power supply frequency. In addition, the instantaneous fluctuation range of the power supply grid is between 10% and 20%, which deepens the light fluctuation of the lighting fixture.
Commonly used stroboscopic index to describe the stroboscopic degree of the light source, the integrated stroboscopic ratio and two other variables: optical waveform and duty cycle. Wherein, the stroboscopic ratio is equal to the difference between the maximum light output and the minimum light output in one switching cycle divided by the sum of the maximum light output and the minimum light output, and the stroboscopic index is equal to the amount exceeding the average light output in one switching cycle divided by the total light output. . The lower the stroboscopic ratio and the stroboscopic index, the less the stroboscopic effect caused by the flashing of the light source.