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KFC UPDATES LOOK WITH NEW LED TECHNOLOGY
When the sun sets, companies depend on their illuminated signage to give prominence to their brand. Good illumination, particularly for food franchises, is vital for attracting customers at night. Light Emitting Diode (LED) technology has become economically viable and is already a serious player in the signage industry, which up to now mostly relied upon neon and fluorescents as light sources. LED Lighting South Africa, based in Salt River, Cape Town, was faced with the task of developing a robust, long lasting LED product to illuminate the white fascia of the new look KFC stores. The result is the LED Light line, developed in co-operation with Milliken Industries. It was approved by Enterprise IG, the branding company for KFC, for its cleaner, sharper and continuous line of illumination. LEDs have numerous advantages including low energy use, low operating voltage, ease of installation, low heat generation and long life. The longer lifespan of LEDs is greatly welcomed by KFC Franchise owners who are responsible for the on-going maintenance costs of their stores. However, as LEDs are still new technology to South Africa, the long life span still needs to be proven in the field. A successful LED solution must consider the following factors: type of LED, ambient temperatures, drive current, reverse voltage, connecting pins, electrochemical action, voltage drop, ingress protection (IP), type of power supply, mechanical fixings as well as ease of installation and transportation to site. An LED without these considerations would not last long in the intense sun in Upington, or high humidity in Durban, or wet driving rain and wind during the Cape Town winters. The KFC LED light line is a culmination of many prototypes which have been thoroughly tested on site under harsh conditions over an18 month period. In the case of the design for the LED Light line, extra thick copper tracks have been used on both sides of the printed circuit board (PCB) to increase the heat dissipation and allow longer lengths to be connected together. LEDs are very sensitive to voltage. A small increase in voltage will result in a large increase in current if no current control is used. When connecting long lengths of LEDs together, if no current control is used, the LEDs furtherest from the power supply will be dimmer than those close to the power supply. The LED Light line is driven by current control circuitry, which means that the current remains constant for moderate voltage changes. This, together with the extra copper, means that up to 20m can be connected in one length. This saves on the number of power supplies requires and facilitates installation. The current control circuitry also ensures that all LEDs receive the same 20mA of current which means that they all burn with the same brightness. If no current control is used, the forward voltage across the LEDs in one string could be different to the next string and a difference in brightness will occur. This difference will result in one string drawing more current than the next. More current means more heat is generated by those LEDs. More heat means it draws more current and so on. This results in what is termed thermal runaway and will lead to premature failure of the LEDs The connections between PCBs need to be robust to withstand vibrations on site. In the case of the LED Light line, these links are soldered on both sides of the PCBs to create a strong, rigid connection.. The LED Light line is encased in water tight UV stable Acrylic tubes with pluggable ends for ease of transportation, handling, maintenance and installation. The LED solution is modular with readily available spares, which can be easily replaced by plugging out one section and plugging in another. The connecting pins between each pluggable LED module are gold plated to minimize resistance and to prevent electro-chemical corrosion UV stable Acrylic tubing is fitted over the pins to create additional rigidity to the light line. The diameter of the tube is the same as that of a neon tube which means the LED light line clips in to standard mechanical fittings for neon. The acrylic tubes were chosen for their excellent optical properties. They have a low light absorption rate and being round means they can be aligned easily to maximize the wash of light. The KFC solution also has transient suppressor diodes, placed on the back of the long lengths of PCB to protect the LEDs voltage surges. LEDs operate best when used with a DC switch mode power supply. Precaution must be taken to mount the power supplies inside, or within a well protected and ventilated box to prevent heat build up and moisture ingress. This showcase illustrates the complexity and ingenuity of using LEDs. It has earned its merits and is a worthy opponent of classical lighting sources such as neon and fluorescents.
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