Caltex South Africa has chosen to use energy efficient LEDs for their forecourt signage illumination. LEDs have been used instead of neon to illuminate the red light line, white star logo and white letter sets. With characteristics such as long life, low maintenance and low energy consumption, it is not surprising that LEDs are fast becoming a major player in many industries not least of which is the signage industry. Globally, the LED industry reached sales of $4.2m billion in 2006. This figure is set to double by 2011, according to Strategies Unlimited, a market research company based in Silicon Valley California. With this massive expected growth, more and more companies are entering the market and supplying off the shelf LED products. But is an LED an LED, or are there differences between them that can affect the look and life of the product? The answer, of course, is that there is a vast difference between a high quality LED and a low quality LED. When comparing an LED from an unknown supplier with that from, say one of the top 10 LED manufacturers in the world, it may be difficult at first to distinguish which one is better. The brightness may even be the same. The difference however will become evident after 1000 hours, or in some cases 100 hours, of burn time. Low quality LEDs can dim by as much as 50% within the first 500 hrs. Some manufacturers quote LED lifespans of as much as 100,000 hrs. The LEDs might in fact last that long, but its light output may have deteriorated so much that you can hardly notice it emitting any light. There are presently no standards available that specifies what is acceptable lumen deterioration. In the US there are many organisations working together to create solid state lighting standards to enable products to be compared on an equal basis. The initial proposal of these standards is that the LED lifespan be rated on either L70 or L50 where the 70 and 50 represent the percentage of the original light output. For example, one manufacturer may state a life of 50,000 hrs at L70 and 75,000 hrs at L50. These life spans would have to be determined in an accelerated test environment since 50,000 hrs is equivalent to 5.7 yrs and no manufacturer will wait that long to release their products. Usually 1000 hrs of accelerated testing is used as the benchmark for extrapolation. The colour of an LED also has an affect on its life span with colours closer to the red (640nm) end of the spectrum demonstrating longer lives (75,000 hrs) than those in the blue (460nm) region (45,000 hrs). This is because the epoxy which covers the LED can be eroded by the shorter wavelengths being closer to ultraviolet light. So what determines a high quality LED? An LED consists of 2 main components – the die and the packaging. Both of which need to be of the highest quality. There are a handful of LED companies that manufacture very good quality dies. Many LED packaging companies purchase these dies and then package them into the various types of LEDs. This process of packaging is critical to ensure that the LED is able to achieve maximum brightness and dissipate any heat build up to ensure that maximum life is obtained. Most reputable manufacturers hold several patents for this packaging process. Research and Development (R&D) is a critical part of any LED manufacturer’s organisation so it is important that they invest a great deal in about 10 percent of annual sales in R&D. Choosing a very good quality LED is not enough however, to ensure that you have a high quality product. Many standard products are not ideally suited to particular applications and customising them can be cumbersome creating installation difficulties as well as potentially affecting the life of the product. For the Caltex light line, a specialist LED design and manufacture company created the solution. The solution incorporates current control on a double sided printed circuit board to allow for up to 20m to be connected in one linear length. This simplifies the wiring and reduces the number of power supplies required. The current control also ensures even illumination across the full length of the canopy and regulates the current to ensure that the LEDs do not overheat by getting too much current. Heat is the major factor affecting LED life. The printed circuit boards are fitted into an acrylic tube, sealed on both ends, with pluggable connectors allowing for each 2m module to be connected together without any noticeable gap in light - a very big advantage over other types of light. Special gold coated pins for external use have also been used to carry the high current when connecting 20 m together. The system runs off 24V so safety is not an issue, another advantage over neon. Since LEDs are solid state light sources, there are very few instances of breakages en route to site. Installation is also done easily and quickly using the same 12mm clips used for neon – the only difference is 5 clips are recommended per 2m length instead of 3 for neon. This ensures that the LEDs are fitted in a straight line which enhances the crisp clean look that the LEDs create. In summary LED quality is critical to ensuring a high quality product, but the design of the product is equally important to create the look and lifespan required for the application.
