Analysis of flicker parameters of several common lighting products

1. Introduction of flicker parameter
Flicker (light source flicker) means that the light output of the lighting source fluctuates with a certain frequency. At present, the international research results on strobe include IEEE std1789, IEC TR61547, CIE TN 006, etc.

1.1. Flicker percentage and flicker index in IEEE std1789
The flicker index refers to the area above the average light output line in a period divided by the total area of the light output curve in a periodic light output waveform.

Flicker percentage or modulation depth refers to the ratio of the difference between the maximum and minimum light output in a period to the sum of the maximum and minimum light output in the periodic light output waveform.

For the flicker index, a flicker index <0.1 is considered high quality light. According to the latest IEEE std1789, the flicker percentage and frequency are considered. Specific low-risk requirements: when the light frequency is <90Hz, the flicker percentage should be less than 0.025 times the frequency; when the light frequency is 90Hz-1250Hz, the flicker percentage should be less than 0.08 times the frequency; when the light frequency>1250Hz, no limit. In order to visually express the degree of risk of flicker, the percentage of flicker is normalized by modulation (NM), and the low-risk requirement is normalized to NM. This NM is marked as NM1, and NM1<1 indicates a low-risk area. Non-hazard requirements: when the light frequency is less than 90Hz, the flicker percentage should be less than 0.01 times the frequency; when the light frequency is 90Hz-300Hz, the flicker percentage should be less than 0.0333 times the frequency; when the light frequency is >300Hz, there is no limit. The same normalization method can be used to obtain NM2, and NM2<1 means no harm.

1.2. Pst in IEC TR 61547
Pst, short-term flicker index, this technical indicator analyzes the frequency range of 0.05Hz-80Hz, which can simultaneously assess the fluctuation of the power supply voltage and the influence of the lighting product’s own circuit on the change of light output. The threshold is 1, Pst<1 is acceptable; When Pst>1, more than 50% of observers will feel the flicker.

1.3. SVM in CIE TN 006
For strobe above 80Hz, the human eye is not easy to detect, but it has a greater impact on the human eye’s spatial perception. For example, some fast-running equipment is regarded as slow-running or even stationary, that is, the flicker effect. CIE TN 006 proposes SVM technical indicators for the flicker effect, and analyzes the frequency range of 80Hz-2000Hz to judge the initial insight of the stroboscopic effect. SVM=1, which means it is just visible; when SVM>1, it means it is visible; when SVM<1, it means it is not visible.

1.4. CA CEC (North American Energy Star)
Flicker percentage test and calculation are carried out under no filter and 40Hz, 90Hz, 200Hz, 400Hz and 1000Hz filter frequency state respectively.
1. PAM without filtering: without filtering, calculate the percentage of flicker directly, no requirement.
2. PAM (40Hz): filter out frequency components above 40Hz, and then calculate the flicker percentage.
Greater than 1%, high risk: less than 1%, low risk: less than 0.4%, no risk.
3. PAM (90Hz): filter out frequency components above 90Hz, and then calculate the flicker percentage
More than 2.25% high risk; less than 2.25% low risk; less than 0.9% no risk.
4. PAM (200HHz): filter out frequency components above 200Hz, and then calculate the flicker percentage
More than 16%, high risk; less than 16%, low risk; less than 6.7%, no risk.
5. PAM (400Hz): filter out frequency components above 400HHz, and then calculate the flicker percentage
More than 32%, high risk; less than 32%, low risk; less than 13.3%, no risk.
6. PAM (1000Hz): filter out frequency components above 1000Hz, and then calculate the flicker percentage
More than 80%, high risk; less than 80%, low risk; less than 33.3%, no risk.

1.5. ASSIST standard (American Semiconductor Lighting System and Technology Alliance)
1.5.1. First test the flicker frequency and flicker percentage of the lighting object, and then calculate the values of d, fb, a.
d: It is the probability of observing the flicker phenomenon under the flicker frequency and flicker percentage.
fb: Under the flicker percentage, the acceptable and unacceptable boundary frequency of flicker.
a: Five-point system estimate acceptability.
+2: Fully accepted.
+1: slightly accepted.
0: between acceptable and unacceptable
-1: somewhat unacceptable
-2: completely unacceptable

1.5.2.Mp, Dp
The value calculated in the first item above does not consider the influence of waveform and spectral components, and Mp considers the influence of waveform and spectral components.
Mp is greater than 1, flicker is visible;
Mp is less than 1, flicker is not visible;
Dp is the probability that flicker can be observed under this Mp value.

2. Test method and result analysis
2.1. Test method
Light source flicker measuring instrument uses the most common incandescent lamps, self-ballasted fluorescent lamps (energy-saving lamps), and LED bulb lamps as the analysis samples. The above flicker indicators were tested in a dark room, and the samples were fully lit and stable before the instrument was tested. Among them, the incandescent lamp adopts 60W incandescent lamp and 200W incandescent lamp. Self-ballasted fluorescent lamp and LED bulb lamp adopt two typical samples (one for better and one for worse) respectively. The results are shown in Table 1.

2.2. Result analysis of each parameter
Most of the detection results in the flicker index are less than 0.1, and only the flicker index of LED light 1 is greater than 0.1.

The light frequency of the lamp this time is 100Hz, so the requirement of low risk of flicker percentage should be less than 8. At the same time, it can be seen that the result of flicker percentage is consistent with NM1 and NM2. If the flicker percentage is high risk, NM1 is also high risk; if flicker percentage is low risk, NM1 is also low risk; if flicker percentage is harmless, NM2 is also harmless.

In the SVM test results, except for LED light 1 indicating visible flicker, the others have no visible flicker.

3. Conclusion
The flicker index, flicker percentage, and normalized NM, Pst, SVM can all clearly characterize the fluctuation of the light source output. However, the frequency and angle of each parameter analysis are different, and the respective thresholds adopt different models and calculation methods, and the judgment results may be inconsistent. Relatively speaking, the limit requirements for flicker percentage and flicker index are more stringent than those of Pst and SVM, and there is no unified international and domestic standards, so we can consider these parameters comprehensively at the same time.

Regarding the new ErP regulations (EU) 2019/2020 and energy efficiency labeling regulations (EU) 2019/2015 of EU lighting products, Shanghai LISUN recommends the following supporting test solutions for flicker test:

1. LPCE-2(LMS-9000) High precision spectroradiometer integrating sphere system can test the follow parameter: Lumen, luminous efficiency, spectrum, color rendering index, energy efficiency rating, power factor, etc.

2. LSRF-3 Lamp start, Run-up time and flicker test system and LSP-500VARC-Pst AC power supply: Designed in full accordance with BASIC, Energy Star V2.1, IEC-Pst, CA CEC, ASSIST, IECTR61547-1, CIE SVM and IEEE Std 1789 standards.

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Tags：LPCE-2(LMS-9000) , LSP-500VAR , LSRF-3