Type B LED T8 tubes have long been the one of most popular choices when retrofitting fluorescent to linear LED. But did you know Type B LED tubes are the most susceptible to flicker? Your eye may doesn’t see it, but it is occurring and can impair us in different ways.

LED Bulbs Flickering

Light flicker has always been an issue for lamps with possible important health impacts. According to the paper “A review of the literature on light flicker: Ergonomics, biological attributes, potential health effects, and methods” that was published by the Institute of Electrical and Electronic Engineers (IEEE) in 2010, light flicker frequency in the 3~70Hz range is highly perceptible by human beings and this could make them very uncomfortable. Even repetitive flashing lights and static repetitive geometric patterns may induce seizures in these individuals, and the occurrence rate is around 0.025%.

Further people are beginning to pay more attention to long-term exposure under higher-frequency flicker in the 70~160Hz range. Such flicker can cause malaise, headaches, and visual impairment. Some researchers even claim the retina can sense flicker up to 200Hz, but tests have shown that above 160Hz the health effects of flicker are negligible.

Types of Flickering

There are two types of flickering with lights – visible flicker and invisible flicker.

Visible flicker is the one our eyes can see, which is when the light output from a given source changes rapidly. It is considered that anything below a frequency of 100Hz can be seen.

Invisible flicker is just as much of a problem if not more. It is the flicker that is present but we cannot see. The symptoms include dizziness, eyestrain, headaches, migraines, impaired thought, and other general sick-feeling symptoms.

Where does Flicker Come From?

To better understand flickering in lights, let’s consider how an LED light source operates. LED light output is almost linear with the drive current. Peruse any high-power LED datasheet and it can be seen the linearity in graphs that plot forward current relative to luminous flux. Such a plot makes it quite obvious that the ripple of drive current is a critical source of LED light flicker.

All LED drivers have a ripple component in the output current, depending on the topology selected, it can be in the order of 1 percent to 100 percent. The frequency of the ripple typically comprises 100Hz or 120Hz (due to 50Hz or 60Hz AC line voltage rectified) and a higher frequency component typically in the 30kHz to 100kHz (due to high frequency switching). It is worth noting that 100 percent ripple is not new in lighting. Low-pressure-sodium streetlights typically exhibit 100 percent output ripple as do EM ballast driven T12 fluorescent tube lamps. 

Single-stage LED drivers are the most widely used by Type B LED tubes in the market today and typically have output ripple current in the order of 30 to 100 percent. By comparison two-stage drivers are widely used by Type C LED tubes and therefore perform much less output ripple, typically in 10 percent below.

How to Reduce Ripple Current?

Increasing output capacitance will reduce ripple current but space left to internal driver for Type B tube is often limited and additional capacitance is expensive. Another alternative is to use a linear regulator that can smooth out the peaks in the ripple current, like as JW1236 or BP5659 etc. While this is extremely effective, the linear regulator components do add a cost burden and reduce the driver efficiency by up to 6 percent. Therefore only a few Type B tube in market place applies linear regulator to suppress output ripple and while her price is high.

Ultimately if the driver design of the LED tube meets the requirements of both a stable DC current and ample ripple suppression, there should be no flicker. If the flickering is present in your LED lamp (and you are not dimming with it), it was likely created with cheap driver components. The technology in LED lighting today has advanced to the point where this should not happen, unfortunately there are companies that care more about their product profits than the health of their customers.

Dimming Lamp without Flickering

Another challenging variable for LED lamps to avoid flickering is through dimming. Most standard wall dimmers work by phase cutting, which removes part of the sine wave and reduces the voltage. However, this can have negative affects on an LED circuit and actually result in the flicker effect being amplified to a potentially dangerous level (3-15Hz range).

It should be pointed out that mostly claimed dimmable Type B tube nowadays are worked by phase cutting, to meet DLC5.1 dimmable requirements but compatible to limited wall dimmer only.

This is one of the main reasons why it’s hard to trust old dimming systems can work well with new LED bulbs. It looks that the only way to be sure a dimmable tube light without flickering should be a Type C lamp works with well-designed 0-10V dimmable driver. It all comes back to the fact that LED is a long-term investment. In turn it is worth doing research to ensure you are getting a quality LED bulb, and that if you plan to dim with it you are getting an LED dimming system that has been tested as being compatible to the LED bulbs you intend to use.