Often there is a debate on which is better, LED Sidelit Panels or LED Backlit Panels. In this article I am going to try and highlight the pros and cons of each of these options. For those of you who have experience in the lighting industry you will know that the LED backlit panel was the initial LED technology that was used to replace the 600x600 and 1200 x 600 fluorescent fittings that would be commonplace in offices and commercial properties. Backlit panels at the time had a deep / thick body and very often we were able to see the positioning of the LED chips through poor diffusers creating a non-aesthetically pleasing LED panel.
To counter this problem sidelit panels were introduced into the market which on the initial viewing was aesthetically a lot more pleasing than the introductory backlit panels.
Soon after the sidelit panels were introduced the competition became fierce for the market share. Many factories tried to optimize and reduce the costs of manufacture of the sidelit panels that had become the preferred technology for commercial properties.
It is important however to understand the components that make up a sidelit LED panel in order to understand the complications that were faced in the market. On the inside of the sidelit panel is one of the most important components called the Light Guide Plate (LGP) that would be responsible for transmitting the light from the edge of the LED panel through to the center of the fitting with an exceptionally smooth harmonious look and feel.
Soon factories introduced a light guide plate (LGP), made of Polycarbonate instead of the acrylic PMMA in an attempt to provide a more economical offering. Soon the market realized that the Polycarbonate lightguide plates would result in the LED panel turning a very unpleasing ugly dark brown or yellowish brown in the center.
The yellowing of the LED panels caused much distress both for building owners and for lighting suppliers, often resulting in conflict and financial accountability.
As was often the case, lighting suppliers who supplied the LED side lit panel that had turned yellow, or brown would claim this to be wear and tear and not part of the warranty of the product even though the light would not perform as per the specifications on the data sheets.
There were however many suppliers in the market who supplied the acrylic PMMA light guide plates, who often faced rejection due to price. Electrical contractors would often procure products based on price and not consider the end customers' liability once the project is complete. Because of the market conflict that existed due to the varying quality of sidelit LED panels, the factories started to manufacture a modernized version of the backlit LED panel. In a recent study that was done by Lux magazine, some of these panels would lose up to 30% of their light output in the first 1000 hours (About 4 months of lighting use). Whilst this is not the case for all backlit LED panels it certainly raises the concern to investigate the claims made by the various factories on the longevity of the LED backlit panel. The latest modern LED backlit panels are manufactured in such a way that you cannot see the positioning of the LED chips and it creates a perfect harmonious light output once installed.
Let us therefore compare the pros and cons of the sidelit LED panel and the backlit LED panel. Firstly, we will consider the lumen output / Efficacy: the LED backlit panel has a higher lumen output and can produce a higher lux level than would typically be available on a sidelit LED panel. Typically, the sidelit LED panels would achieve 100 to 120 lumen per Watt whereas the backlit panel can comfortably reach up to 180 lumen per Watt. (Fitting lumen not source lumen).
Secondly, we will look at heat management: the sidelit LED panel is positioned in a T grid in the ceiling with the LED's being on the side of the fitting. The LED's are subject to heat management both in terms of conduction of heat as well as convection. The conduction of heat will transfer from the side of the LED panel and will be conducted into the ceiling T grid where the air circulation in the office space will disperse the heat away from the T GRID and in fact keep the T GRID relatively cool, thus protecting the LED panel. Therefore, from a heat management perspective the sidelit LED panel is an exceptionally good technology. However, when you consider the heat management on a backlit panel it needs to be considered that the LED chip testing (LM80), is conducted at an ambient temperature of 25 degrees. It is also the case when testing the LED fittings on LM79 and TM21 that the ambient temperature is set to 25 degrees. However, when a backlit panel is installed in an office or commercial property the operating temperature of the ceiling void is most likely to be much higher than 25 degrees. Given that the LEDs are placed on the back of the LED panel and do not make any contact with the T grid the only form of heat management is convection because the panel has no heat sink of itself. Technically the LEDs are placed in the ceiling void albeit only three centimeters into the ceiling void, the temperature to which they are exposed can comfortably vary up to or even higher than 45 degrees centigrade. Now here we Introduce the 11/57 principle. When considering the life of LED fittings, it is important to note a remarkably interesting statistic. If the junction temperature increases by 11 degrees centigrade the lifespan of the LED chip decreases by 57%. This statistic is significant in determining the longevity of an LED fitting. Conclusion: Careful attention should be given to the application and requirements of a lighting project. Whilst the backlit panel can have a much better efficacy and consequently the Quantity requirement for LED panels can reduce significantly, the end clients can fall victim of panels that will need replacing significantly earlier than anticipated. For more information about this or to hear of the potential solutions to this matter please contact Genesis One Lighting at sales@genesisone.co.za
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