Any rapid and repeated changes in brightness of light are called light flickering. When a light is flickering, it remains flutter and unsteady. It happens because of the voltage changes supplied to the light source or when the power line voltage fluctuates.
The intensity of the flicker depends on some factors. These are:
- The range of the voltage fluctuation.
- How much of a voltage change happens.
- The type of light includes an incandescent, fluorescent, LED (light-emitting diodes), or HID (high-intensity discharge lighting systems).
- The gain factor of the lamp.
- The number of light in the lighted area (ambient light levels).
Types of Flicker:
Flicker is mainly two types. These are:
Visible: You can perceive visible flicker consciously, and it is considered uncomfortable. It has harmful effects on humans.
Invisible: Invisible flicker is not consciously perceived. However, it may still have biological and health effects on humans. Most humans are not able to perceive flicker in the light above 60-90 Hz.
How Do You Check Invisible Flickers?
It is easy to identify visible flickers, but it is not equally easy like the visible one when it comes to invisible flickers. LED lights with flickers are not good for human health. So we should be able to identify whether the light has flicker or not.
Here we show you an easy way to identify the invisible flickers:
First, open your smartphone camera in slow motion video mode. Then point it towards the light source. After that, you may notice a visible distortion. This visual distortion is invisible flickers.
Flicker percentage and flicker index are measures to quantify flicker and determine LED lighting quality. These two flicker measures are defined in the 9th edition of the IESNA Lighting Handbook . Flicker percentage is a measure of quantifying the amount of flicker at a given frequency. It is a relative degree of the cyclic difference in the output of a light source, for example, percent modulation. Flicker percentage is, therefore, sometimes also known as the modulation index. A smaller flicker percentage implies lesser flicker.
Impact of Flickers:
Flickers create negative impacts in the human body. Studies show that flickers can be the cause of headache, eyestrain, weakness, etc.
Impact of Visible Flicker:
Neurological problems, including photosensitive epilepsy in sensitive people, can result in very short exposures of visible modulation (3 to 70 Hz range). The estimated prevalence of this problem ranges from 1 per 100 000 to 1 per 4000. It most commonly occurs during adolescence, and 75% of these individuals remain sensitive throughout life.
Impact of Invisible Flicker:
- Invisible flicker is transmitted through the retina, and this flicker may create headaches and eye strain. A number of studies have shown that the modulation from cathode ray tube displays and fluorescent lamps affects eye movements.
- Research shows that it creates severe migraine headaches. A survey conducted in 2010 and published in the Journal of Light and Visual Environment concluded that 22% of responding migraine sufferers cited flicker as a triggering factor for their migraine.
- It Increases repetitive behaviour among people suffering from autism.
- Asthenopia (eyestrain with nonspecific symptoms), including fatigue, eyestrain, blurred vision, headache, and diminished sight-related task performance occurs because of invisible flicker.
- It also creates the stroboscopic effect (in which objects in motion appear to slow down or stop) and related apparent stoppage or slowing of rotating machinery.
These impacts are very serious for every human body. We have our eyes open for around 6,000 hours a year, and most of this time, we are exposed to artificial light, so imagine the impact of LED on our eye and overall health over prolonged exposure. If you are an office goer, you might have experienced headaches, eye strain, or dizziness, and the culprit could be the invisible flickers of LED lights installed at your office. In certain industrial settings, LED flicker can lead to performance issues and even mishaps.
Children are suffering more as they are exposed to LEDs in schools, homes, malls, and elsewhere. Studying for long hours under LED lights with high flicker can cause eyesight problems in children. The same goes for teenagers who spend a considerable amount of time reading and preparing for exams.
Factors that make Flicker Worse:
Certain conditions worsen the adverse effects of flicker. These are:
- longer duration of exposure,
- greater area of retina receiving stimulation,
- central location in the visual field as it projects to a greater area of the visual cortex,
- greater brightness of the flash and higher contrast of the flash with the surrounding luminance.
It is necessary to note that the biological effects of flicker are a function of several factors. These include flicker characteristics (mainly frequency and modulation depth), features of the stimulus (luminance, spectrum, size, contrast), individual characteristics (individual differences in sensitivity, adaptation state of the eye), and others.
Is There Any Safe Limit for Flicker?
As we already know that flicker is harmful to eye health. There is not much awareness on this subject, and there are no regulations on LED light flicker levels yet. However, IEEE standards PAR 1789, California has set the threshold limit of 30%. This is important to note that LED products from different brands available in the market have flicker percentages varying between 40 to 80 percent, which is much higher than the safe limit of 30%.
Is There Any Solution to Solve The Limit Problem?
Yes, there is. While flicker cannot be brought to zero levels, it can certainly be reduced without impacting the performance of the LED light. The key to mitigating flicker lies in the LED driver, eliminating the problem by supplying the constant non-oscillating current to the LED.
We already know that flickers are harmful . But due to the multitude of advantages, such as less power consumption, better efficacy, and longer life, flickers containing LED lights are rapidly taking over conventional lights with increased commercial availability. The severity and range of flicker are relatively very high when compared to conventional lights. That’s why, the development of flicker quantifying measures are increasing by global lighting standards and specification communities.