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 the last article, the basic concepts of stroboscopic and flashing, the meaning of luminescence stability, and the illuminating principle and luminescence stability of various light sources (lights) were discussed. This article will focus on the luminescence stability test and data analysis of several lamps.
First, the luminous stability test of several lamps
According to conventional wisdom, the human eye begins to "critical" to see that the stroboscopic light change should be a combined effect of the cycle time equal to the "visual persistence" effect time of the human eye and the light intensity fluctuation depth of 25%. According to the principle, the regularity of the 50Hz frequency-powered illumination lamp has a photoperiod of 0.01S, which is much shorter than the “suspension effect†time of the human eye, 0.05~0.15S, in the “visual persistenceâ€. "The same amount of light came before the end of the effect time. At this time, people felt that there should be no strobe.
In this study, for various light sources (lamps) operating at 50 Hz alternating current, the change of luminous flux is measured from the preheating of the lighting to the stabilization, and the rate of change of the luminous flux is calculated. When the luminous flux change rate is large, the luminous stability is poor, that is, the possibility of stroboscopic is large. This is the same as the definition of "fluctuation depth" H = (φmax - φmin) / φmax × 100%, but this definition is also an indirect parameter of stroboscopic.
Experimental principle: The shorter the integration time (equivalent to sampling or exposure time) during measurement, the closer the result is to the "fluctuation depth". Measuring the stability of the luminous flux value for each half-wave of a continuous period of time will lead to a more direct conclusion of how the strobos are obtained. For example, for a lamp with a power supply of 50 Hz, the luminous flux of each half wave for several seconds or longer is continuously measured, and if the luminous flux between each half wave changes little, the luminescence is stable. If there is a repetitive fluctuation in the period of time greater than the "visual persistence" effect time, and the amplitude exceeds 25%, it is considered to have stroboscopic.
The shorter the measurement integration time, the higher the accuracy of the measurement equipment and various other conditions, and the corresponding measurement error or uncertainty may also increase. Therefore, if limited by the equipment, it is possible to indirectly draw conclusions by randomly measuring the luminous flux values ​​of short durations at different discontinuous times.
This experiment is limited by the spectral integral measuring device. The shortest integration time measured is 50ms, that is, the average luminous flux value of 2.5 cycles or 5 half-waves in 50Hz is measured each time. The device cannot measure continuously, and can only randomly measure the average luminous flux value of 5 half-waves at each discontinuous time.
The first judgment basis of this experiment is: For the stroboscopic study with a "visual persistence" effect time of 0.05 seconds, assuming that the luminous flux of the five half-waves is 100 lm, the average value measured is 100 lm. The most extreme case of light change is that the luminous flux of the 10th half wave in the 6th to 10th half waves is increased by 25% (critical) while the luminous flux of the other four half waves is constant and still 100 lm. At this time, the average luminous flux of the sixth to tenth half waves is 105 lm. Therefore, the rate of change of the "average value of the first to fifth half waves" and the "average value of the sixth to ten half waves" is 5%. Then, as long as the rate of change of all luminous flux values ​​measured many times throughout the experiment is less than 5%, it is indirectly indicated that there should be no stroboscopic. The greater the amount of data measured, the more accurate the results are. On the other hand, even if the measured result is greater than the critical value of 5%, there is no certain stroboscopic.
For example, if the luminous flux of the 1st to 5th half-waves is 100 lm, the luminous flux of the 6th to 10th half-waves increases the luminous flux by 6% on average, which exceeds the critical value of 5%, but The brightness of the first to fifth half-waves in the human eye is far less than 25% of the brightness of each half-wave of the "6th to 10th half-waves". Therefore, it cannot be judged that strobe will occur.
The second point of the experiment is based on the comparison of test data such as incandescent lamps that have been comfortable for a long time and which do not feel stroboscopic, and the degree of luminescence stability and stroboscopic light of other lamps are estimated.
The lamps used in this test include incandescent lamps, fluorescent lamps under inductive ballasts, fluorescent lamps under high-frequency operation (energy-saving lamps), unidirectional LED strings, and LED strings that are bidirectionally connected in parallel, and high-frequency conversion to LED bulbs under direct current. Wait. For the accuracy of the conclusion, the measurement of the three integration time of 50ms (0.02S), 100ms (0.1S) and 300ms (0.3S) of the small integrating sphere system and the measurement of the large integrating sphere system with the integration time of more than 10 seconds were carried out. . Measurements of similar similar test conditions were performed to verify the repeatability of the results.
50ms (0.02S): shorter than the "visual persistence effect" time of the human eye, the lamp working for 50Hz AC is equivalent to the average of the luminous flux of 2.5 cycles (5 half cycles);
100ms (0.1S): equivalent to the average retention time of the human eye, the lamp working for 50Hz AC is equivalent to the average of the luminous flux of 5 cycles (10 half cycles);
300ms (0.3S): The persistence effect time longer than the human eye. The lamp for 50Hz AC operation is equivalent to the average of the luminous flux of 15 cycles (30 half cycles).
The experiment was carried out under the same environmental conditions and power supply stability (monitoring the change to 220V ± 0.1V about 0.05%). Through the test data analysis of various lamps, the consistency and stability of the instrument is very good. The effect of this measurement conclusion, which is expected to have a luminous flux change rate/relative value, is negligible.
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