Philips Lumileds, more reliable and efficient LED thermal analysis method

Philips lumen (Philips Lumileds) expert Dr Michel Kruger recently published an article about accurate LED heat calculation methods of effective articles, this paper details the about can increase the accuracy of the thermal analysis of white leds and simplify the process of analysis. The following is Dr M hill Kruger published in full. 
Today, the thermal analysis of white leds is still an unfinished science. Most of the LED lamps and luminaires manufacturers can only rely on inadequate and inaccurate or fuzzy data to determine the LED device performance in the field of related applications, this can often lead to the excessive heat sink design engineering. 
Commonly used in industry power conversion efficiency (WPE) method to calculate the LED to the power required by the optical radiation, and LED the heat generated by the actual. WPE flaw is that the same product category it is concluded that the result of the differences between each LED equipment, make it hard for manufacturers of lamps and luminaires to LED products in the comparison. Moreover, WPE usually also had a lot to do with operating environment. We will introduce a kind of simple and clear, based on the radiation (LER) of the LED luminous efficiency calorific value calculation method. The most advanced, fluorescent transformational white leds LER is generally constant, so the illuminator designer can use this formula to estimate the heat generated by the LED device quickly. 
Leds and heat dissipation 
In the thermal simulation experiments, the LED will sometimes be modeled as a simple resistive heater, all will enter the LED electric power assumes that will convert into heat and, in turn, spread from the illuminator. But the assumption that there is a problem, that is too conservative: high brightness fluorescent transformational white leds are typically 30% into the electric power is converted to light, and blue LED the transformation of the power can be considerably more than 50%. Therefore, the total power needed for the high brightness LED fever is usually lower than into the total electrical power leds. 
If a lower heat capacity inappropriately in thermal simulation, the internal temperature of the illuminator is expected to too high, so will need to adopt more complex and higher cost of heat sink design. This for those who need to spread from small PCB and heat sink specific heat (5 w - 10 w) application is particularly important, such as type of LED bulbs. Should assess the total thermal performance of lamps and lanterns or illuminator, the designer must be reasonable to consider the incoming electrical power will be converted to the proportion of light and heat. 
Now the LED industry commonly used WPE method is defined as the LED total radiated power and the incoming LED the ratio of total electrical power. Because the WPE depends on the nominal voltage, flux and the LED and is actual drive current and temperature is strong function, so in the same category of products differences in the results between different LED devices. Thus for specific LED products category, the hard drive to according to different conditions, the flux and voltage BIN definition of a typical WPE values. 
Radiation luminous efficiency 
In contrast, when evaluating LED application of heat to use luminous efficiency of radiation (LER) more convincing than WPE, the former light visible light emitting efficiency can be measured. More specifically, LER was defined as the total of the light source to adapt to the luminous flux (lumens) divided by the total radiated power (watts). LED the LER value can directly from the radiation spectral power distribution (usually printed in the equipment data sheet), and unlike WPE, LER values are not for the nominal flux and voltage or the actual drive current and connect the temperature change obviously. Under the condition of known LER value, can LED the total calorific value of calculated through the following formula: 
Among them, the diamond symbol LER value, If said drive current, Vf said operation under the condition of positive pressure, v operating conditions of the total luminous flux. For example, for a typical LER value is 300 lm/Wrad fluorescence transformational white leds, assuming that the drive current is 1000 ma, luminous flux is 300 lm, forward voltage of 2.9 V, then according to the above formula can calculate the total calorific value of 1.9 W. 
The current fluorescent transformational white leds production technology progress to make the same product category LED point of accurate color control, so LER value more consistent. In fact, such as Philips lumen (Philips Lumileds) manufacturers such as the latest LED lighting level (3 order MacAdam ellipse) has excellent color control can be realized. This allows the manufacturer to define a specific CCTS, can represent typical LER value of the same product category all leds. 
Philips has already started to use LER value in "calculator" LED system, which makes the LED system designer can be found through this tool used for its final lighting application of key performance indicators, including the system heat and light. In this way, philips could help designer to design more easily meet the expected requirement, heat sink costs associated with a lower lamps and luminaires. In addition, the use of LER value can more easily on the comparison to different manufacturers of the same category LED, enhances the transparency and simplify the procedure of the LED specification. 

----------Archled Technology Co.,Limited