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We all know that LED is a semiconductor light emitting device, the semiconductor device is a heat-sensitive, which means that it is very sensitive to temperature. Or that the temperature will directly affect its performance and parameters. As an electrical - optical conversion device of its most important indicator is the number of watts of electrical power input, how much light output (lumens), which we call light efficiency (luminous efficiency), this indicator represents the most important indicator of quality of the LED. The user is required according to his luminous flux (lumens) to choose the lowest wattage LED.
However, although the device itself has a LED light effect, but does not mean that users will be able to enjoy the luminous efficiency directly, because this LED lighting device will be assembled into the loss of part of the light effect. Let us not consider the mask transmittance (assumed to be 100%, in fact, usually around 90%), while the main LED light source itself to consider the light effect. This light effect we are also divided into two kinds of thermal efficiency of luminescence efficiency of light. Most people probably will not notice the difference between these two luminous efficiency, so we are here to discuss the first light luminescence efficiency and thermal efficiency issues.
1. What is the effect of what is hot cold light effect
Simply put luminescence efficiency LED light source that is at room temperature (25C) when measured luminous efficiency, light and heat efficiency is measured and other light effects LED light source after thermal stabilization. Specifically, we usually integrating sphere to measure efficiency LED light source, the power measured immediately after the luminous efficiency is obtained luminescence efficiency (assuming that time at room temperature is 25 degrees), the "immediately" About 5 within seconds. The thermo-optical effect is to wait at least half an hour to three quarter of an hour to reach thermal equilibrium (or heat-stable). Now we usually say that the light effects are luminescence efficiency, or that we usually indicated on the packaging or in the shell luminous efficiency indicators mostly luminescence efficiency.
For most users, they are mainly concerned with actually thermo-optical effect. Because LED lighting is the use of more than half an hour, unfortunately, only the user knows the luminescence efficiency of light fixtures do not know the heat efficiency of the lamps, which in a sense, this is an unintended outwit consumer behavior.
Anyway, I suggest that in the future should be based on a thermo-optical effect as the light efficiency targets, marked on the box.
2. luminescence efficiency and thermal efficiency of light how different
Here we look at the effect of cold and hot light effect in the end there is much difference. To better understand the differences between our various well-known brands of LED PAR lamp cold light effects, specifically to the United States and Japan to buy several well-known brands LEDPAR lights for the actual test results obtained are as follows:
Wherein the start value after power is measured immediately, the end value is the value of the test after waiting half an hour later.
For example Philips 432 195 type bulb lumen output, after half an hour, reduced from 1860lm to 1680lm, reduced to 92%. Specifically lumen depreciation process is shown below.
In fact, half an hour is not yet fully reach the stable value, you may also need three quarters of an hour or an hour to genuine stability.
Above table can be drawn the following conclusions:
(1) light effect the start and end values for all of the brand LED lamps is different.
(2) a minimum difference of 0.97 and a maximum of 0.86
Difference (3) of the input power and thermal characteristics LED is actually unrelated.
(4) differences in luminous efficiency is mainly due to the LED junction temperature rise due.
(5) junction temperature rise can not be avoided, because the LED itself is only about 40% efficiency, the other is converted to heat, thus increasing the heat after power up, and finally rose to the value of thermal stability from room temperature. But the size of the increase in value is related to the quality and the radiator. Radiator better temperature lower. Therefore, in order to reduce the difference in thermal efficiency and light luminescence efficiency, it should be possible to adopt good radiator.
3.LED light engine cold light effect
Why should we study special LED light engine cold light effect, this was because the light engine has its special. The so-called light engine is actually put into the LED light source LED power supply is also where the aluminum substrate, this way, the power LED power consumed are also released on the aluminum substrate, which increases the aluminum plate to the heat, but also will increase in the future LED junction temperature thermal stability. Here is an example to illustrate the current market, the most common is a non-electrolytic capacitors light engine, its power efficiency is usually only about 85%, which means there will be 15% of the input power is converted to heat and added aluminum substrate. Assume that the total input power of 10 watts, is applied to the remaining 8.5W LED, the luminous efficiency of LED itself is assumed as 40%, which is only 3.4W of power into useful light, there are 5.1W power into heat. Originally aluminum plate as long as the heat dispersion 5.1W now to add 15% of the power is 1.5W of heat, for a total dispersed heat 6.6W, an increase of 29.4% of the heat, close to 30%. The aluminum plate thermal resistance did not change, it means that the power to increase the temperature rises, the temperature of the aluminum substrate increases, meaning that the same aluminum plate LED ambient temperature, junction temperature with increasing , the result is reduced luminous efficiency.
The actual test results 4. LED light engine thermal efficiency and luminescent light effects
We tested a Shenzhen company produces 60W light engine without electrolytic capacitors, as well as Real Green Lighting Company's production of electrolytic capacitors 60W light engine. Both the shape of the photo as follows:
1:Shenzhen company no electrolytic capacitors 60W light engine
2:Real Green Lighting electrolytic capacitors 60W light engineWhen tested using the same radiator, so different from the two cooling affect the test results. Both the total flux of light engine changes with time the results are as follows:
2:Real Green Lighting electrolytic capacitors 60W light engine
The total flux from the former just getting machine 5780lm, after half an hour down to 5120lm, declined by about 11.4%, and the downward trend from the point of view, it should be further reduced over time to 5000lm. The Aifei Lai's engine light flux dropped from 7233.8lm to 6486.8lm.
Input power of the two curves as shown below:
1:Shenzhen company no electrolytic capacitors 60W light engine
2:Real Green Lighting electrolytic capacitors 60W light engine
Shenzhen company because light engine also uses power compensation (see above), its input power within 30 minutes increased from 57.81W to 59.53W. So it's light efficiency is reduced from 100lm / W to 86lm / W, reduced by 14%. If the heat flux is finally stable after 5000lm, its last light efficiency is only 84lm / W, down 16%. While its nominal light efficiency is 100lm / W, if the luminescence efficiency from the point of view, or to achieve, but if the heat from the light efficiency point of view, it is the difference of 16%.
5. The difference between the various non-electrolytic capacitor light engine
Although we only measured a certain company, one of our products cold light efficiency difference. Some may raise this is the point behalf of the face, less comprehensive advice. If the accuracy of the data, it is indeed the case, but if the results approximate data, these results are a great representative. In fact, the reason is very simple, resulting in the difference between hot and cold light efficiency of the main reasons is because of the low efficiency of the current source and the light source is integrated into the aluminum substrate together, thus causing the LED junction temperature than those without constant current source junction the temperature is higher, so it's certainly hot light efficiency is low. For switching power supply, it is possible to achieve efficiency of 95%, but because of the switching power supply device, large volume, it is impossible to be integrated into the aluminum substrate. So now all integrated into the aluminum substrate to have a linear power supply only. Of course, the type of linear power supply, there are many, and now with the most is a segmented light lit no electrolytic capacitors engine, there is a direct constant current diode electrolytic or non-electrolytic capacitor light engine, but whether it is which linear power supply, its efficiency curve is exactly the same, are the mains voltage increases linearly decreases at 220Vac is about 85% (see figure below).
The efficiency of all linear current source
The Real Green Lighting although a constant current source is a linear constant current source, but due to the intelligent adaptive adjustment technology, making its efficiency up to 99% (see figure below).
Conclusion
From here we come to an important conclusion is that: Only high efficiency constant current source to be able to be integrated into an aluminum base plate made of a light engine, they are not because of the low efficiency constant current source LED junction temperature increase and reduce its thermo-optical effect. The low efficiency constant current source is integrated into the aluminum plate is to improve the results of the LED junction temperature, thereby reducing its thermal efficiency, and the difference this cold light efficiency is much greater than the differences between conventional LED lamps, in the above example the difference up to 15%.
Therefore, we should require that all light engine LED lighting manufacturers should be the thermo-optical effect indicated on the product packaging. So as not to mislead consumers.
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