How do Driverless High Bay Lights work?
LEDs (light emitting diodes) have become an increasingly useful lighting technology for all kinds of everyday purposes. Normally, the continued operation of an LED light requires that it be fitted with a driver; this is an electrical circuit which keeps the current within a certain range, high enough to make sure the LED is powered but low enough to avoid causing permanent damage. The requirement for high bay LED lights to have these drivers comes with a number of annoying downsides. Now however, the advent of driverless high bay lights is going to change all of that. But how can these lights work without a driver?
How LEDs Work: A Quick Refresh
LEDs contain a semiconductor which releases light. Unlike traditional bulbs which rely on light released from a vacuum or a gas, LEDs get light from solid matter, and so are classified as a kind of solid state lighting (SSL). When a high enough voltage is applied to the semiconducting material, electrons move across and enter "holes", releasing photons(particles of light) as they do so.
The earliest versions of driverless LED technology worked via a circuit in which the AC line is converted to direct current (rectified), and then directed through a series of LEDs for which the necessary amount of forward voltage is only just below the maximum voltage of the AC power line. In series with this line of LEDs is placed a resistor which holds the current at the requisite level for the proper, continued functioning of the LEDs. A flash of white light is emitted by this circuit at a frequency of 120 flashes per second, giving a light quality which is quite similar to what you would obtain from a fluorescent tube ballasted by magnets.
This design was improved through the introduction of a switching system. Placing a switch for each LED in a parallel circuit to the first allows for the number of LEDs in the series to be altered at will. A number of different systems for operating this switch mechanism have been conceived; some replace the simple resistor with a resistor controlled by current, or a circuit with a current limiter. One disadvantage of this kind of circuit arrangement is that the high voltage switches required for the switching mechanism can be quite expensive, as can the IC controllers.
The LED current that you obtain from a circuit with this kind of segmented switching system looks like a succession of half sine waves, whereas the input current looks like a sine wave. As a result of this, the circuit exhibits a high ratio of real power to apparent power, and quite low total harmonic distortion.
However, the output resembling a half sine wave means that at a frequency of 120 Hertz the flicker approaches 100%. This flicker is generally less noticeable than that seen with the first kind of circuit, since there is always a certain level of LED current flowing and so there are always some LEDs switched on. Nonetheless, the flicker can still be detected by some people, at the edges of their vision especially, and so many are still not satisfied with the quality of light that this arrangement produces. Furthermore, there is substantial evidence that even a non-perceptible flicker can still be detected by the brain, and have deleterious effects on performance.
Getting Rid of the Flicker
The newest design for driverless high bay LED lights removes the flicker entirely, through a clever reworking of the circuit architecture. In this new system, the LED current is held near constant, and the output current only experiences a 1.5 ms pause two times in each power line cycle, to allow the capacitors to recharge.
Since this circuit arrangement results in a frequency of over 600 Hertz, the flicker is much too rapid for the human eye or brain to perceive, making the light appear completely flicker-free to all people, and removing any potential deleterious effects. And unlike previous designs, this new architecture does not incorporate expensive power switch chips or IC driver chips.
How the New Architecture Works in Detail
We can understand how this new circuit architecture works if we begin by following the path of the current from the power source. As the voltage increases at the left side of the power source, two of the capacitors receive a displacement current; a current is then sent through one of the LED arrays and back to the power source.
When the input voltage reaches a certain threshold level, an extra current flows through another of the LED arrays, one of the diodes and one of the resistors. So first, we see a displacement current flowing through the LED arrays, followed a bit later by a galvanic current.
As the input voltage is increasing, a third capacitor is charged up to the maximum level via another one of the diodes. By this means, two of the capacitors operate in alternation; one is recharging, while the second is discharging. The moment that the potential difference of the input power source rises above or below nought, the ready charged capacitor can immediately deliver a full output current. As the displacement current begins to go down towards the middle of the half cycle, the galvanic current in turn is seen to start increasing and so maintains the LED current for a longer period. Overall, we get a reasonable stable output current over quite a long period.
A prototype design of this circuit architecture had total LED current flowing through all of the strings of a 19W light engine. This experimental version delivered 93% electrical efficiency, with a THD of 24% and a power factor of 0.53.
Details in Practice
Four strings of LEDS wired in series, turning on one after the other, create the light output. Simulations show that the sum of the current is quite consistent. Each of the strings only becomes excited once every 16 ms. To obtain the uniform light output that we want, the LEDs have to be arranged very closely in sets of four, and then these sets of four need to be arranged to enough proximity so that together they produce an LED forward voltage which is similar enough to the voltage of the power line. There is a large ripple current which does not suit electrolytic capacitors, so the inclusion of ceramic capacitors is a better choice.
This circuit architecture is suitable for a huge range of different lighting products, so long as the overall design of the product allows for the LEDs to be placed in the geometry described above.
Advantages of the New Driverless Technology
With the LED driver and the burdensome consequences of its necessity removed, a great new space of creativity and innovation becomes open. LED products can be made in square, rectangular and circular shapes as well as many others. Lighting products can be made into different sizes and shapes without this affecting their performance. The overall design is simpler, flatter and more compact. The flatness means that the LEDs can extend to great lengths, over 100ft, and still be controlled by just a single switch.
The high flicker rate seen with previous incarnations of LED high bay lights made them unsuitable for many common purposes, such as lighting an office building or a mechanic's workshop. The introduction of a lighting technology with no detectable flicker means that high bay LED lights can now be installed in such contexts.
The driverless LED high bay lights are easier to transport and cost less to manufacture than previous solutions. They are also less expensive to buy and run, which will save you money in the long term on both replacement lighting and energy bills.
Having no drivers will also greatly reduce maintainance costs. Drivers will occasionally break down and need replacing; this can be a difficult process, requiring specially trained workers and equipment to be carried out, and costing you a significant amount of money. It will also create the inconvenience of having to either close your premises for a long time while the work is carried out, or visiting the premises and staying their for a long time out of normal hours. Installing driverless technology will remove all of these problems.
Installing driverless high bay LED lights is a much quicker and easier process than with previous kinds of light. The driverless lighting solutions weigh less and involve less complicated fitting. This will save you money on labour costs for the initial installation.
While many previous LED designs have not been dimmable, driverless LEDs are able to be dimmed, providing a more versatile and adaptable lighting solution for environments that require the provision of a variety of different light levels under different circumstances.
Opt for Driverless High Bay LED Lights
If you're looking for a functional, efficient high bay LED lighting system than look no further than this new driverless architecture. The improvement on the previous forms of driverless architecture has not only made these lights suitable for a huge range of different settings from commercial to industrial and so on, but has made them the best solution outright.
Advantages in efficiency, manufacturing costs, maintenance costs, installation costs, aesthetics, practicality of design, room for innovation, imperceptible flicker and ability to dim mean that driverless LED technology is the ideal choice for any high bay lighting system.