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What is the life of a lamp?

Every time dealing with lighting business sales, will repeatedly mention a word: warranty. Each manufacturer announced the warranty time is not the same, there are two years warranty, a three-year warranty, but also five-year warranty.
However, in many cases, the seller himself does not understand, from what the warranty time is estimated, or just with the flow of the LED should be so long warranty?
Today, Xiaobian take you into the LED world, find out how the lamp life in the end is how to define and judge.
First of all, when it comes to LEDs, we can tell from the outside that it differs from a traditional light source at a glance because almost all LEDs have a significant feature - the heat sink.
 
A wide range of radiators is not for the beauty of LED lamps, but to make the LED a better job.
Then you will be wondering why the previous light source uses less heat sink, and almost all the LED lamps are used in the LED era radiator it?
That is because previous light sources were glowed by thermal radiation, such as tungsten lamps, which rely on heat to shine, so they are not afraid of heat. The LED's basic structure is a semiconductor P-N junction, the temperature is slightly higher, the working performance will decline, so the heat is crucial to the LED.
First, let's take a look at the LED's composition and schematic
Tips: LED chip will work fever, we put its internal PN junction temperature referred to as junction temperature (Tj)
 
In our daily life, LED luminous flux will be with the junction temperature decreases, as shown in the junction temperature of 25 ℃ when the standard value, the junction temperature to 100 ℃ when the luminous flux is only 80% Around
 
And, most importantly, the life of the LED luminaire is closely related to the junction temperature.
 
One concept that needs to be understood is that when we talk about LED lifetimes in general, it does not mean that it burns down. When the LED light output reaches 70%, we think it will end.
It can be seen from the above chart, if the junction temperature control at 105 ℃, then LED lamps to about 10,000 hours, the luminous flux decayed to 70%; and if the junction temperature control at about 60 ℃, then it to 100000 + hours, the luminous flux Will be reduced to 70%. Life expectancy increased by 10 times.
In our daily life, the most common thing we encounter is that LED life of 50,000 hours, in fact, is a junction temperature control at 85 ℃.
Since the junction temperature of the LED lamp life has played such an important role, then how to reduce the junction temperature? Do not worry, first look at how the lamp is cooling, understanding the way of cooling, naturally know how to reduce the junction temperature.
Lamp cooling way
The three basic ways of heat transfer are conduction, convection and radiation.
Radiator main transmission channels for conduction and convection cooling, natural convection radiation cooling.
Pass the basic principles of heat
Conduction
The way the heat travels from the higher temperature part to the lower temperature part.
 
What are the factors that affect heat conduction?
1. Thermal conductivity of heat sink material
2. Thermal resistance caused by thermal structure
3. Thermal conductive material shape and size
radiation
High-temperature objects directly emit heat phenomenon
 
What are the factors that affect thermal radiation?
1. The thermal resistance of the surrounding environment and the medium (mainly considering the air)
2. Heat radiation itself, the characteristics of the material (generally darker out of the power of radiation larger, in fact, the radiation transfer is not particularly important, because the lamp temperature is not too high, the radiation is not very strong)
convection
By gas or liquid flow to heat transfer
 
Factors that affect heat convection
1. The flow of gas and its velocity
2. The specific heat capacity of liquid and the flow rate and volume
 
▲ Figure, the same shape of the radiator, the right heat capacity is better than the left.
In the LED lamps, the radiator in the lighting costs accounted for a big piece. Some manufacturers in order to save costs, in the structure of the radiator, materials and designs shoddy, resulting in serious problems aftermarket lamps.
 
Having said that, in fact, just paving the way for now is the point.
In the end how to determine the cooling of the lamp is good or bad?
The most authoritative of course, is the use of professional equipment to test the junction temperature.
 
However, such a professional equipment may be prohibitive to the average person, then we only use the most traditional way to touch the lamp to sense the temperature.
So in the end the lamp is hot or not so hot?
Hand touch the radiator is very hot, certainly not good
Hand touch the radiator is very hot, the cooling system must not be good, or the radiator cooling capacity is not enough, the chip heat can not be distributed in time; or effective cooling area is not enough, there is a lack of structural design
Hand touch light body is not hot, not necessarily good
When the LED lamps work properly, a good radiator must be lower temperature, but the lower temperature of the radiator may not be like.
 
Small chip heat, good conduction, heat enough, feel the temperature is not high. This is a good cooling system, the only "downside" is a bit of a waste of material.
 
If the substrate below the impurities, there is no good contact with the radiator, heat does not come out, gathered in the chip. Touching the outside, in fact, the chip has long been hot.
Here, Xiaobian recommend a very easy way - "half-hour illumination method" to determine the cooling is good.
Note: "half hour illumination method" from the article: How to determine the advantages and disadvantages of LED lamps and lanterns heat? ← Click on the title to read Author: Ding Deliang
Half hour illumination method
We said earlier, the general LED junction temperature increases, the luminous flux will decline. Then, as long as we measure the illumination changes in the same position, we can deduce the change of junction temperature.
 
▲ "half hour illumination method" indirect measurement of junction temperature changes
First of all, choose a place from the outside light interference, lighting lamps.
After lighting, take a photometer to measure, for example, 1000 lx.
Keep the position of the lamp and the illuminance meter unchanged, after half an hour, then take the illuminance meter to measure, 500 lx, indicating that the luminous flux decreased by 50%, which has been hot to die, touch the outside is quite good, indicating that the heat did not come out, very difference.
If the measurement is 900 lx, illumination decreased by only 10%, then the description is a normal data, heat well.
 
"Half-hour illumination method" scope of application
We list several commonly used chip "flux vs. junction temperature" curve, you can see from this curve, the luminous flux decreased by how much lumens, you can indirectly know how much the junction temperature rose to degrees Celsius.
Column one:
 
▲ OSRAM S5 (30 30) chip, the luminous flux is 20% lower than 25 ℃, the junction temperature has exceeded 120 ℃.
Column two:
 
▲ OSRAM S8 (50 50) chips, the luminous flux than the 25% drop 20%, the junction temperature has exceeded 120 ℃.
Column three:
 
▲ OSRAM E5 (56 30) chip, the luminous flux than the 25% drop 20%, the junction temperature has exceeded 140 ℃.
Column four:
 
▲ OSLOM SSL 90 white chip, the luminous flux decreased by 15% than 25 ℃, the junction temperature has exceeded 120 ℃.
Column five:
 
Luminus Sensus Serise chip, the luminous flux than the 15% drop at 25 ℃, the junction temperature has exceeded 105 ℃.
As can be seen from the above figures, if half an hour after the hot state of illumination than the cold down 20%, basically the junction temperature has exceeded the chip tolerance range. Basic can judge the cooling system failed.
Of course, this is the case in most cases, all have special cases, as shown:
 
Of course, for most of the LED, we can use half an hour illumination method, within 20% decline to determine whether it is good.
Learn it, after the selection of lamps and lanterns must pay attention to Oh, you can not just look at the appearance of lamps and lanterns, use your eyes to choose lamps.

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