Learn about Lightwell Driverless LED High Bay Lights
The AC-LED is composed of a simpler driver circuit for the LED engine as compared to the standard AC/DC drivers hence making it a potential for more possibilities which the solid-state lighting (SSL) body has been exploring. Despite that, most intellectuals have been, until recently, reluctant towards the use of the AC or the driverless light engines. This is due to the claims that the light had a flicker index of about 0.32, but today, there is a new technique used in the AC-LED light engines. This technique utilizes higher frequencies to remit a flicker index of around 0.15 simultaneously fused with a power strand of 0.9.
The flicker index is a conception that has existed since 1952, and its compadre theory of percentage flicker was initially given meaning in the year 2000. The flicker concept first came to the limelight in the 1970s when an interconnection was discovered between the flicker in the magnetic ballasted fluorescent light and the eye strain and headaches that a small percentage of majorly office workers suffered as they worked with these lights on. Following this discovery, the magnetic ballasted fluorescent light systems were gradually replaced with the high-frequency electronic ballast fluorescent lights all through the 1990s. This saw the complaints of eye strain and headaches cease.
How the Flicker and Frequency Problems are Evolving
Up until 2015, LED luminaires and lamps had gained popularity hence widespread use. However, flicker issues have been a concern across a wide range of the SSL products designed for general illumination and other poorly designed products that utilize the AC/DC drivers. The focus here is mainly on the AC-LED technology since flicker is just one of the few concerns that are restricting the extensive adoption of the technology.
In 2015, a regular driverless AC light engine was tested that year and the light output outlined a 0.309 flicker index at 100% flicker. This simply reflects the reality that the instant light output reaches zero at certain points through the line power cycle. A comparison was made with a regular halogen replacement lamp that uses LEDs, the light output outline indicated a 0.105 flicker index.
The standard measures of the percentage flicker and the flicker index both contain a weakness. They have all failed to take into account the aspect of frequency sensitivity of our eyes. Sam Berman among other researchers managed to assemble a group of daring volunteers for a study in 1988. The volunteers had electrodes connected to their eyes to pick up the impulses of electricity coming from high-frequency light pulses through the optic nerves to their brains. The results revealed that the sensitivity decreases quickly as the frequency increases. The sensitivity reduced by around 1000× on a 200 Hz frequency at maximum. This is the reason why some experts have at times been suggesting that all frequencies over 200Hz be filtered out in order to represent what our eyes perceive.
The Lighting Research Center at the Rensselaer Polytechnic Institute recounted a flicker metric that shows the sensitivity of our eyes, from the assumption of the frequencies that half of the subjects could perceive. Nonetheless, earlier research by E.M. Jaen in the year 2011 showed that the human visual performance is usually degraded when in the presence of high-frequency flickers. This was true even when the subjects taken into account were incapable of directly perceiving the flicker.
Something that is clearly noted here is that half of the population is not able to perceive flickers above 60Hz as the LRC documents. On the other side, Berman works show that frequencies of up to 200Hz get transmitted to the human brain. Jaen confirms that the quality of visual performance is lowered despite the subjects not being able to perceive the flicker. A 5 milliseconds time period frequency corresponds to the 200-Hz limit. This clears out the point that any gap in a wavefront in the order of around 2 milliseconds or less cannot be perceived because the human eye is unable to detect and signal the presence of such fast events. This is the knowledge that can be used as a basis for circuits that simultaneously achieve high power factor and low flicker index.
The Birth of the Driverless Technology
Previous descriptions have shown, with the help of circuits, what is considered to be the fourth generation of the driverless AC-LED light engines. A circuit used acquired a power factor higher than 0.7 (which is appropriate for the Energy Star consumer applications) with a 0.28 flicker index. At that time, this was better than any of the AC-LED light engine available. Basically, current controlled resistors (CCRs) are used to achieve better light voltage regulation and standard voltage surge-protection components have also been added to the new light engines. One notable characteristic of those light engines shows that the underlying two LED strings produce light per half cycle while the outer two LED strings produce light per every other half cycle.
The light produced from the two strings on the outer side emerges from the upper string on one-half cycle and from the lower string on the other half cycle. For the light outputs to blend uniformly, each of the LEDs from the topmost string has to be placed as close as possible to the corresponding LED from the string on the lowest part. In order to reduce the number of components, the integrated LED pairs are exerted on each LED component rather than using discrete LEDs.
How it Actually Works
Earlier driverless engines plainly rectified the main then used a resistor to restrict the current. In such arrangement, the AC power line gets rectified and then applied to a string of LEDs. The total forward voltage required was less than the maximum voltage of the AC power line. A resistor in a chain with the LEDs restricts the current not to exceed the rating of the LED. This kind of circuit produces intensive light flash at 120x per second. This results in a light quality similar to that of the magnetic ballasted fluorescent tube.
This arrangement was made better by adjusting the number of the LEDs chained with the power line; switches were simply operated across the line cycle. A variety of arrangements have since been developed for use in controlling the switches. At times, the current-limiter circuits or current controlled resistors are used instead of the common resistor. The circuits come at an expense of costly IC controllers and high-voltage switches.
Light Engine Performance
This light engine exhibits an interesting characteristic in its light output waveform - the modulation operates at frequencies too high for the normal human eye to perceive. Previous descriptions have stated that a better approximation to what our eyes can sense can be achieved by putting the light emission through the 200-Hz low-pass filter. A 4th-order Butterworth filter was used in this case. A percentage flicker which was almost 100% was reduced to 22% as the light output waveform was filtered in correspondence to the human eye capability.
The light engine had its light output increase as the input line voltage increased, that is, a 10% increase in the line voltage produces a 6.4% increase in the light output. However, the dimming performance of this light engine draws attention. The circuit contains small capacitors, therefore, the capacitive dimmer or the electronic low-voltage [ELV] dimmer has to be used. This gives the product the ability to be dimmed to 2.8% without causing any instability. As the dimming increases, the flicker index increases, a process that is similar to that observed with the AC-LED driverless light engines.
In general, the previously mentioned 2015 tests done on a number of the AC-LED light engines showed that they all had an approximate of 0.32 flicker index. In 2016, the Photalume light engine came with a performance of 0.15 flicker index. This was made possible by storing up small amounts of energy on the chip capacitors then releasing the energy at the appropriate time. This results in a driverless light engine which is flat, efficient and combines a 0.90 power factor with a 0.15 flicker index.
An Example With Practical Details
Considering the operation of this kind of circuit at an SSL system level, we take an example of a light output from a four string LEDs operating in sequence. We also assume that each string is electrified once every 16 milliseconds.
For the desired consistent light output to be produced, one of the LEDs from each string has to be mounted together in an array of four. These arrays then have to be loaded together until their total LED forward voltage matches the power line voltage. Ceramic capacitors are used here since the electrolytic capacitors are unable to withstand the huge ripple current involved. This architecture is proposed to be used in a wide array of products so long as the form aspect allows for proper arrangement of the LEDs. This kind of light engine is preferably suited for cove lights, under cabinet lights and task lights in a consumer environment.
Putting aside the physical limitations of the LED drivers, luminaire designers are now offered an all-new platform to design from. All shapes whether rectangular, square or circular can be possibly designed. Light engines on the other side can be made in a variety of sizes and shapes while maintaining the performance. Even better, products with more advanced features, continuous light output and improved power factor are still under development. This offers the lighting industry an opportunity to look forward to a new transformation in products owing to driverless technology.
The Importance of The Technology
The lighting industry and the solid-state lighting industry have found it worth to appreciate the improvements and power of the AC-LED light engines (also referred to as driverless LED light engines). As a fact that, most of the prime luminaire companies rely on the AC-LED based products to make up to half of their sales. It is clear, from the appeal of the complexity and cost perspective, that the small driver circuit can be put on a circuit board which hosts the LEDs without the need for a separate driver module. The latest implementations in this tech combine up to 93% of electrical efficiency with no perceptible flicker and low cost.
AC-LED light engines come with a variety of advantages. First is the compact and flat form factor made possible by the elimination of the LED driver hence making the luminaire design simpler. However, most of the products on the market these days suffer from the 120-Hz flicker - almost 100%, while the efficiency is basically only about 83%. The high flicker leaves them unacceptable to a most of the lighting designers. They are not considered suitable for lighting applications in areas such as workshops and offices. Despite this, the new driverless LED light engine works perfectly in any of the environment a lighting designer would want them on. This technology as said offers a higher efficiency as compared to other products.
This technology offers us products that are cheaper to manufacture and transport, lighter and easier to install. Generally, the products offer us flicker-free lighting and improved energy saving as opposed to the traditional high bay lights and the older LED lights. The product promises even more savings as a result of reduced maintenance costs as there are no drivers or light bulbs needed for replacement. Consequently, no labour costs for maintenance which is usually very high and requires to be conducted out of the normal working hours and with the help of expensive specialist equipment and personnel.