Electronics Protection - Summer 2014 - (Page 6)

Feature New High Efficiency LED Technology Benefits from Best Practice Thermal Management Design Dr. Jack Josefowicz, Thermal Management Consultant C-Therm Technologies New advances in lighting, featuring long life light expectancy light source devices, have been shown to have improved photometric performance and energy saving advantages compared to legacy high pressure sodium (HPS) lighting [1]. In recent years, the front runner lighting device has been the light emitting diode (LED). Other light sources such as plasma devices and induction lamps have also seen modern developments for street and area lighting. However, the conversion of conventional high pressure sodium based lighting has been led by conversion to LED device based luminaires, which can offer an energy saving of 70 percent over HPS lighting. Organizations such as the IESNA, US DOE, ANSI, CIE and NEMA have all focused and developed guidelines for LED device performance prediction over time and especially depreciation projection methodology. Much activity has been focused recently on test methods for photometric characteristics and other LED attributes. Further, based on the historical 'in the field' performance of LEDs over a 50 year period, where LEDs were first introduced as a practical electronic component in 1962 [2], it is widely accepted that LED devices have reached a level of technological maturity that offers up to 100,000 hours of use when they are properly de-rated and not overheated or over driven. To maximize the efficiency and overall performance of LED devices and the light fixtures that they are designed into, it is important to keep the operating temperature as low as possible. This can be affected by the use of innovative materials that can act as interposers to draw the heat away from the LED devices so that their operating temperature is reduced, which improves overall efficiency of the light over its lifetime. Additionally, power supply electronic systems that power LEDs and their reliability also depend on their operating temperature. Therefore, if the power supply enclosure can be filled with a material (potting compounds) that draws heat away from semiconductor components, reliability can be improved. Investigations of novel materials for the purpose of thermal management can be enhanced using the TCi thermal conductivity analyzer, based on the modified transient plane source (MTPS) technique, and allowing for the quick and accurate measurements of thermal conductivity and effusivity of new materials during their development. For many light sources that are now using LEDs, such as desk lamps, flashlights, ceiling lights, street lights, the device of choice is a high brightness white light LED (HBLED). A LED is a two-lead semiconductor light source that resembles a basic pn-junction diode, except that an LED also emits light [3]. Often, when reference is made to the temperature at which the LED device operates, the term "junction temperature" is used. Junction temperature is the highest operating temperature of the actual semiconductor in an electronic device. In Figure 1, the location of the junction in an LED device is identified to be the interface between the n-type semiconductor and the p-type semiconductor, which together forms the LED. In most typical HBLEDs the efficacy (defined as the number of lumens radiated from the LED divided by the plug watts input) is significantly affected by the operating temperature of the junction, as shown in Figure 2. In figure 2 it is evident that the overall efficacy of the 6 Summer 2014 * www.ElectronicsProtectionMagazine.com Figure 1. A LED device showing the location of the junction Figure 2. Efficacy of a HBLED as a function of junction temperature lighting fixture, in this case a street light, is directly impacted by the operating junction temperature of the LED devices. Optics and power supply efficiency are also important factors. Another important impact of the LED junction temperature during operation is the lumen maintenance. This relates to how much the LED output decreases over time as it ages. An example of HBLEDs that have been monitored for output versus time is shown in Figure 3. Figure 3. HBLED light output (lumens) versus time at different operating temperatures http://www.ElectronicsProtectionMagazine.com

Table of Contents for the Digital Edition of Electronics Protection - Summer 2014

Editor's Choice
New High Efficiency LED Technology Benefits From Best Practice Thermal Management Design
Passive Thermal Management of Lithium-ion Batteries Using Phase Change Materials
Considerations for Powering Military Applications
How Thermal Ground Plane and Compact Air-Cooled Heat Sinks are Revolutionizing Thermal Management
Access Control Solutions for Railway Infrastructure
20 Data Center Downtime Study Puts Focus on Maximum Protection
Cooling and Shielding in the Right-Sized Enclosure
Industry News
Calendar of Events

Electronics Protection - Summer 2014