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What is LED strobe and detection and evaluation means?

351 Published by admin 07 15,2018

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The development of intelligent lighting is very rampant, but the lighting products are often highlighted by stroboscopic problems after the addition of dimming, communication and other functions.Stroboscopic safety and health problems will be brought about. International standards on stroboscopic safety have been issued one after another.This paper makes a brief analysis of the current stroboscopic evaluation concerned by international organizations and suggests efficient detection and evaluation methods.

I.What is stroboscopic

LED strobe refers to the light flux of an electric light source fluctuates at a certain frequency.You can often find streaks by pointing your phone at a light source, which is caused by strobes.Some degree of flicker will not cause attention, there is no physical discomfort; But some strobes are a real problem.In the early 1990 s, there is a lot of research found that light stroboscopic and migraine headache, neurological diseases such as autism, visual fatigue and discomfort, there is a close relationship, serious can cause illusion, make the eye causing accidents.Don't underestimate the stroboscopic effects of different frequencies and wave depths.

1. Visible strobe
The human eye is a very complicated system, individual difference is very big, for the vast majority of people, can detect the light flashing, 80 hz at this time of the human eye can perceive light and shade change, flicker frequency at 80 hz, also known as the visible stroboscopic (visible flicker).Visible stroboscopic lighting is not acceptable for normal lighting or display.

2. Stroboscopic effect
For stroboscopic flicker above 80Hz, the human eye is not easy to detect, but has a great influence on the spatial perception of the human eye.Consider moving objects, for example, as a series of still images, called Stroboscopic effect.As a result of the strobe effect, people may have the illusion, and it is very dangerous to regard some fast running equipment as slow running or even static.

II. stroboscopic effect machine from illusion

3. Phantom phenomenon

Similarly, when light flicker frequency at 80 hz - 2 KHZ, and environment in the static object, the human eye in the mobile position or direction, static light spot, but there will be a system known as the phantom phenomenon, such as car tail lights, or scanning outdoor LED display, etc.

4.Stroboscopic hazards

Light source strobe is closely related to many kinds of neurological diseases such as migraine, headache, autism, eye fatigue and blurred vision.Studies have shown that low-frequency scintillation light from 3-70hz May trigger photosensitive epilepsy in some people.For 100Hz scintillation frequency is recognized to cause headache and migraine;The twinkle light with a frequency of 120Hz May affect people's mood, causing boredom, anxiety, etc.The visual illusion that the stroboscopic effect is in tune with the associated mechanical movements is dangerous in industrial Settings.Therefore, accurate measurement and evaluation of the stroboscopic properties of lighting products are directly related to people's health problems, which need to be solved urgently.

2. Why does LED flash

Turn LED lighting products adopt AC DC constant voltage or constant current power driver, do not produce stroboscopic light source itself, with or without stroboscopic depends on LED drive power supply due to drive differ in thousands ways, each LED products stroboscopic performance is different also.
In particular, some manufacturers, in order to save costs, use a relatively simple drive circuit, such as AC LED, will have a large stroboscopic problem.

For intelligent lighting products, dimming is an essential function, and dimming is just another inducement leading to strobe.
When the product is loaded with dimming function, the strobe will be further intensified.
Especially when the light is dimmer, its fluctuation depth is larger, as shown in the figure below.
Therefore, for lighting products with dimming function or claimed to be able to connect the dimming controller, the stroboscopic performance of the dimming controller should be measured when the dimming is at its brightest and dimming respectively.

III. Related stroboscopic evaluation criteria
At present, several international standardization research groups have conducted in-depth studies on stroboscopic topics, and have or are publishing standards or technical specifications, including the following categories:

1.Energy star and IEEE

North American energy star product certification standard is the earliest stroboscopic to requirements for lighting products, one of the standard, in fact, as early as 2000 the IESNA lighting has been in the manual of stroboscopic clear definition and requirements are put forward.

2015 IEEE file, stroboscopic risk can be divided into several levels, as shown in the figure below, the level of green area coverage is risk free, while the yellow area is low risk classes, more than the yellow part is not acceptable.

2. California regulations

In 2015 a California CEC regulations issued by the measurement and evaluation methods of stroboscopic put forward different requirements, the requirements in 40 hz and 90 hz and 200 hz and 400 hz and 1000 hz cutoff wave conditions, calculate percentage modulation, in general is more complicated.

3. The IEC standard

The flicker frequency covered by IEC is 0.05hz-80hz.
The visual stroboscopic stroboscopic stroboscopic values (Pst) were evaluated in the standard.
In the calculation, the subjective visual perception of the fluctuation of illumination is simulated, and the severity of the flash during this period is evaluated by calculating the graded probability of the instantaneous flash visual acuity.
With Pst =1 as the limit, when Pst >1, more than 50% of the observers will feel the strobe.

4. CIE technical committee

In the first division of CIE's technical committee on stroboscopic techniques, the SVM index was used to evaluate stroboscopic effects, covering the 80hz-2000hz band, which has been used in the U.S. department of energy's Caliper report.
Dr. Dragan Sekulovski, chairman of the technical committee, and the research team of southeast university of China have done a lot of research in this field

5. The recommendation method is ASSIST

The LRC has released three recommendations for stroboscopic semiconductor lighting systems and ASSIST, one for visible stroboscopic stroboscopic stroboscopic effects and two for stroboscopic effects.

6. Comparison of standards

The above standards have different focus and calculation methods.
Dutch philips, finishing a part of the standard limit comparison, discovered that the most demanding of the IEEE, the Pst and SVM respectively of different wavelengths, and consider the waveform of the measured object and the duty ratio, the more accurate, and therefore more recommended.
In addition, the us department of energy (DOE) has organized webcasts to popularize the flash assessment.

Ⅳ. How to measure strobe

Is the method that mobile phone takes a picture to identify stroboscopic reliable?
Open the phone's camera and lighting products to be tested, by observing for streaks in the phone's screen to judge whether the product is blinking, the method can reflect the part of the problem, but it is not entirely correct, not to mention the objective science.
Professional measuring equipment is required to evaluate stroboscopic problems quantitatively.
And according to the standard requirements, the measurement strobe should use the photometric probe to collect data, the sampling rate should be at least 2kHz above, the faster the better.

1. Field testing

There are high requirements on the mobility and human - machine interaction of equipment for field measurement.
Remote sfim-300 spectral scintillation illuminometer is a kind of equipment specially developed for field measurement.
The fast changing optical output waveform can be recorded in real time, and the output waveform can be analyzed in time domain and frequency domain, and the parameters such as stroboscopic index and stroboscopic percentage can be obtained.

2. Laboratory certification level measurement
The remote lfa-2000 light source stroboscopic measurement system is mainly used for laboratory measurement, which can be used to measure the benchmark frequency, scintillation index, scintillation percentage and light fluctuation depth of lighting products.In the 2016 DOE survey report, the remote lfa-2000 was rated highly by field measurements.

3. The strongest stroboscopic measuring tool

Combined with the latest standards and technical specifications, a new generation of stroboscopic measuring equipment, lfa-3000 light source stroboscopic analyzer, has been introduced in the distance.
The device has excellent performance both in hardware configuration and software function.

The device is equipped with a fast photometric probe with a maximum sampling speed of 100kHz, which can capture fine waveforms of rapidly changing light sources.
Illumination measurement range: 0.1 lx ~ 200,000lx, suitable for most dimming lighting products.
Each index of the instrument can satisfy the requirements of the latest standard measurements, and carrying the tablet, which can realize remote control and wireless data transmission, can be applied in the laboratory, and can be applied in all kinds of field measurement occasions.

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