11 years ago, the 1st generation LED lighting products came to the market. Then the LED efficiency is keeping increase during these 11 years, nowadays it already as 3-4 times as the 1st version. In this post, we are going to discuss some nuances and details of LED package/encapsulation and integrated lighting fixture, which are easily overlooked. And will do a comparison with traditional lamps, like CFL, halogen, incandescent and HID bulb etc.
Efficacy (LED Efficiency)
The efficiency of LED lights also be called efficacy – lumens output per watt (LM/W). LEDs also have its own efficacy, and it is different from the efficiency of LED light. Because an integrated LED lamp with a housing, driver (internal/external design), cover/lens, so for lamp we need consider about its heat dissipation ability, driver efficiency and light loss (and there also has difference between different LED lamps). But the efficacy of LEDs and LED products both depends on some same factors, such as the electrical and internal quantum efficiency.
Only consider about the LED package/encapsulation, there also many factors need be considered. But 3 of them need pay more attention – 1.the way of white light generating; 2.color quality of light; 3.working current of the LED.
- There are two methods to produce white light LED – color mixing and phosphor conversion. The phosphor conversion has a higher efficacy, which also be called PC-LED. At present, the top PC-LED with a 170-180LM/W efficacy. So, most LED lights we are using today with this kind LED as their light source. But the CM-LED with a better potential, it surely will get a higher efficacy than PC-LED in the future.
- About the light color quality, it’s a really detail. When you want a specific color temperature LED, you need change the spectral content of phosphor before the encapsulation process. But at the same time you also changed the luminous efficiency of radiation (less lumens output), which means the LED efficiency be influenced, too. So, here we have to talk about the connections between efficacy, CCT (correlated color temperature) and CRI (color rendering index). To achieve the high CRI, LED needs a wider spectral power distribution. So, the LED packaged as high CRI series, with a lower LED efficiency. And we all know that the higher CCT LED is brighter than lower one – same LED, its 6000K cool white type has 15-20% more luminous than 3000K warm white LED (but in theory, they should have the same lumens).
- LED has different working current, from 350mA to 1000mA, and some special high power LED even with a higher drive current. LED driven by higher current with more lumens output, but the efficacy of this LED is lower. In other words, high drive current with higher total lumens output, but the low drive current LED with higher lumen efficacy, which be called EFFICIENCY DROOP.
The heat dissipation, driver and optical loss all influence and reduce the efficacy of integrated LED lamp, and all of these factors will cut down around 26% efficacy of LED luminaires. Compare with LED efficacy, the energy efficiency data of LED light is more closed to actually applications. Former data is similar with the laboratory data.
Effect from heat dissipation
P-N junction temperature is the biggest factor, which influence LED lights’ luminous efficacy. When this temperature increase, the efficient of lighting generating will get down, make less lumens output. So, good heat dissipation ability is very important for LED lights. But no matter how good the lights’ design is, the junction temperature still much higher than the laboratory data – at least leads a 15% decrease of LED efficiency.
Effect from driver (power supply)
Fluorescent lamp and HID light need a starting voltage & limited current, which offered by the ballast. Same to the LED light, there it is a LED driver, which transforms the high voltage to low voltage, and makes the DC constant current input to LEDs. But most LED drivers’ efficiency is around 85-90%, which need keep improving, too.
Effect of lighting loss
Every LED lamp has an optical system to arrange its lighting distribution, like the lenses, cover, reflector etc. Cover has various type – transparent, milky, corrugated etc. and considers about the material, it can be PC type, PS type and also glass/PMMA type etc. All of these lighting distribution systems have different beam angle, which designed for different application requirements. This lighting loss reduces the LED light efficacy, but looks like we have to living with it at present.
The application efficacy
What is application efficacy? The cost efficiency of a lighting application, which is right achieved as your exactly requirements. With an example maybe will help you better understand it. For a display cabinet lighting application, spot light or T5 tube light? And which one has the higher application efficacy? I think everyone can figure out the right answer easily. Yes, the LED spot light with a better application efficacy (things displayed in cabinet need accent lighting), because it is the exactly right option for this lighting application. This example also tells us that forget about try to use a poor (looks like ok) light to replace the right one/professional design luminaires. Just like someone who wants to use tube light to replace LED grown lamp for saving some money.
And the application efficacy is also an advantage of LED light compare to the CFL lamp, incandescent bulb and HID light. Because most traditional lights (except halogen) with a 360°emitting direction, but LED lights beam angle can be from 5°to 360°, which is adjustable (flexible design possible) to meet your lighting requirements.
So, find the right lights for the application is VERY IMPORTANT! It helps you get the real efficiency.
There is an advantage be mentioned by LED light manufacturers every time – Maintenance-Free. LED luminaires’ low lumen decay performance is making itself with a really high maintenance efficacy. If you LED lamp’ quality is as good as enough, you will never spend even 1 second on their maintenance within the next 10-20 years (LED bulb-2008, tube light-2009, LED ceiling lamp-2010, panel light-2011 installed in my house and office, up to now we haven’t any problem from them).
Lamp efficacy comparison
Compact fluorescent: 60- 65LM/W
Linear fluorescent: 80-95LM/W
High pressure sodium: 110-130LM/W
Metal halide: 100-120LM/W
LED: 120-160LM/W and keep improve
LED efficiency is substantially improved after the 1st generation light came out, and still keeps increase. Its efficacy already doing much better than traditional lamp and the replacement to the old lights is on the way (GE Stops Making CFLs, Says Go, Go, Go To LEDs). From this post we also learn about that when you going to buy some lights, not only pay attention on the LED efficiency, but also need think about the CCT, CRI, beam angle etc. Of course, you can’t forget the dimming function if it is necessary – all of these factors are help us to do the high efficacy energy saving!