CCTV 3 + 15 exposure LED strobe, about stroboscopic these things, you know?

The development of intelligent lighting is rampant, but the lighting problems are highlighted after lighting, communication and other functions. Strobe will bring about health and safety issues, and international standards on strobe have also been introduced, but the standards of different departments have different focus, and the evaluation indexes are also very different. This paper makes a brief review of the current international organizations' attention to stroboscopic evaluation, and suggests efficient means of detection and evaluation.

First, what is strobe?

Strobe is the fluctuation of luminous flux of electric light source with a certain frequency. The alignment of light sources with a cell phone can often be found in stripes, which is caused by flicker. Certain levels of strobe do not attract attention or physical discomfort, but some strobe problems are really a problem. In the early 90s, there are a large number of studies have found that migraine, headache, stroboscopic light source and autism, visual fatigue and discomfort is closely related to neurological diseases, serious will make human caused illusion, causing accident. Do not underestimate the stroboscopic, different frequency and depth of fluctuation, the impact on people is not the same!

1. visible strobe

The human eye is a very complicated system, the individual difference is very large, for the vast majority of people, can be aware of the following 80Hz light flashing, the human eye can perceive the brightness changes, flicker frequency below 80Hz is also known as visible strobe (visible flicker). Visible strobe is ordinary lighting or display unacceptable.

Sensitivity weighted function of eye to strobe

2. strobe effect

For more than 80Hz strobe, the human eye is difficult to detect, but it has a greater impact on the human eye's spatial perception. For example, a moving object is considered as a series of stationary images, called Stroboscopic effect. Because of the stroboscopic effect, people create delusions, and it is dangerous to see some fast running equipment as slow running or even stationary.

Strobe effect

The machine running illusion caused by strobe effect

3. phantom phenomenon

Similarly, when the light source flicker frequency in 80Hz-2kHz, and in the environment of the object is stationary, the human eye in the mobile position or direction, but there will be still light spot extension system, called the phantom phenomenon, such as car taillights, or scanned outdoor LED display etc..

4. strobe hazards

Light source strobe is closely related to migraine, headache, autism, eye fatigue, blurred vision and many other neurological diseases. Research shows that the low-frequency flicker 3-70Hz light source for some people may cause photosensitive epilepsy; for 100Hz frequency were found to be the cause of headache, migraine; for the 120Hz frequency of the flickering light source may affect people's emotions, appear tired and anxiety. The visual illusions caused by the stroboscopic effect and the associated mechanical motion are very dangerous in the industrial arena. Therefore, the accurate measurement and evaluation of the strobe characteristics of lighting products are directly related to people's health problems, which need to be solved urgently.

Two, LED why strobe?

LED lighting products with constant voltage DC or AC constant current source driver, light source itself does not produce stroboscopic, stroboscopic depends on the LED drive power because the drive performance of each different strobe LED products are not the same. In particular, some manufacturers use simple driving circuits in order to save costs, such as AC LED, there will be a big flicker problem.

For smart lighting products, dimming is its essential function, and dimming is just another cause of the flash. And when the product loads dimming function, strobe will tend to be further intensified. Especially when dimming is dark, the depth of fluctuation is large, as shown in the following picture. Therefore, for lighting products with dimming functions or that can be connected to the dimmer controller, the strobe performance shall be measured at the brightest dimming and dimming times respectively.

The flickering waveform of dimming LED lamps

Three. Strobe evaluation criteria

At present, there are many standardized research teams in the world, which have carried out in-depth research on the subject of strobe, and have been or are releasing standards or technical specifications, mainly including the following categories:

1. energy star and IEEE

North American Energy Star products certification is the first standard for lighting products made by one of the standard requirements of the strobe, in fact, as early as IESNA lighting handbook in 2000 has put forward the definition and requirements of stroboscopic clear.

The 2015 release of the IEEE file, the stroboscopic risk is divided into several levels, as shown below, the green coverage is not the level of risk, while the yellow area is low risk, more than the yellow part is not acceptable.

Low risk (yellow area) and level of unawareness (green areas below)

2. California regulations

Put forward different requirements on the stroboscopic measurement and evaluation of the 2015 release of the CEC regulations in California, in section 40Hz, 90Hz, 200Hz wave, 400Hz and 1000Hz, calculation of the modulation percentage, overall is more complex.

3.IEC standard

IEC covers a light flicker frequency of 0.05Hz-80Hz. The standard flicker frequency Pst is used to evaluate the visible flicker. In the calculation, the subjective visual sense of human eye to illumination fluctuation is simulated, and the severity of flicker in this period is evaluated by calculating the probability of visual sensitivity of instantaneous flicker. At the limit of Pst =1, more than 50% of observers will feel strobe when PST>1.

Pst has been calculated