LED Lighting Design
Beyond basic application interfacing, a realm of complex variables further complicates an otherwise strait forward LED lighting design. Environmental factors such as ambient temperature, humidity, and sun light will affect the basic operation and reliability of the LED light. Hot and humid conditions are generally bad. Therefore, considering the worst-case condition offers a baseline for engineering procedures. LED datasheets generally state operating criteria at room temperature. However, graph data usually offered subsequent to typical operating conditions provides data relative to alternative environments. A derating curve offers the maximum forward drive current according to temperature. Some datasheets offer lifespan or reliability data according not only to temperature, but also to humidity. It is important to consider this data while engineering an LED lighting solution with potential exposure to a fluctuating environment.
Custom Lighting Example
To further ones understanding of custom lighting, consider the following custom LED lighting solution. The objective is to design an LED array for a civilian airport lighting application, known as a PAPI. A third party designs and manufactures the housing component, originally engineered to meet strict Federal Aviation Administration regulations. Corresponding electronics are required to fit within the confines of the housing, and must operate from a particular power grid installed at the airport. Assume that optical requirements call for a red or white light visible from a distance of five miles during daylight. A successful overall design does not only depend upon specific optical requirements, but also on the mechanical and electrical compatibility with corresponding housing. Dimensional restrictions and mounting criteria are carefully considered. The interior volume of the housing will generally have a direct affect on thermal properties. In addition, mechanical connections with the housing can dissipate heat, theoretically creating a heat sink. Ventilation is also important. A common practice is strategically placing electronic components that generate excessive thermal energy in direct proximity to any openings or vents in the housing. Assume the airport's primary power grid operates at 120 volts AC, single phase, at 60 Hz. A high-grade linear power supply will function as a buffer between the primary power grid and LED circuitry. The supply's output rating is 48 volts DC with a maximum current of 12 amps. The linear power supply's voltage and current specifications provide a mathematical foundation necessary for engineering the corresponding LED circuitry.
The holy grail of white LED backlighting for displays is in designing the best method to illuminate a large area by disseminating the LED light source uniformly eliminating hot spots and minimizing darker areas all the while keeping the parts cost down and ensuring that the final assembly is quick and easy.
LEDs are easier to use and have a longer life cycle (50,000 hrs. Max) to half life and run on less DC power eliminating the need for external inverters to power them but are still able to be dimmed and have a wider temperature range.