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led lamp

LED is the abbreviation of light emitting diode.The basis part of led lamp is led chip which is also called light-emitting semi-conductive. There are following processes from led chip to led lamp:

1.Curing the led chip to the substrate by silver plastic or white plastic

2.Connected with PCB board by gold wire or silver wire

3.Encapsulation by epoxy to protect the inner led chip and wire.

4.Installation of the bottom case

Led lamp is the most important part of LED screen, it will influence whole vision effect of the led screen.

We often see 2121,2727,3535 led lamp on the led market,but what is the meaning of those number? It’s the size of the led lamp. Such as 2121 means the size of led lamp at 2.1x2.1mm (w*h) .Knowing this will help us to choose led lamp. When we know the pixel pitch of screen, we can check whether the led lamp is suitable for the screen or not. Such as P2.5mm usually uses 2121 led lamp but no 2727 on the market,because P2.5mm means the distance between two pixels is only 2.5mm. There will be no enough place to insert two led lamps if using 2727 lamp since one lamp size is 2.7mm. Same as that P1.875 will use 1515 but not 2121 etc. So if we see configuration of P2.5mm screens’ led lamp is 2727, we should recognize that it is wrong specification.

But for outdoor led screen,it usually uses 2727 ,3535,3528 led lamp etc. There are enough space to insert 2121 led lamp, but why not choosing 2121? Because outdoor screen have high brightness requirement.The led lamp size also means the led chip size. For 2121 led lamp, it is hard to increase the brightness because led chip is too small to enlarge the current passing. So at this time we will consider choosing big size led lamp to reach the high brightness requirement. That’s the reason why we choose big size led lamp for outside application.

Most of time we will face a question that is why at same color and brightness, led will have big difference at price? The difference is because of LED reliability, luminous degradation, led lamp design and technology etc. Low price led most of time adopts small size led chip and rough electrode, sometimes even uses poor material to cut down the cost. But it will absolutely shorter the lifespan of led lamp and cause fast luminous degradation problem. So when you meet same color and brightness but at very cheap price, then you should consider the material question.From longtime consideration it will lose money than choosing high quality led screen at beginning.

What will influence the led lamp’s lifespan?

1.The quality of led chip.This is most important factor.

2.The technology of encapsulation. Poor encapsulation technology will cause the heat dissipation problem.

3.Reasonable led lamp design: related with conductive,heat dissipation etc.

4. Driving method. There are constant current and constant voltage driving method. Constant current driving method will longer the lifespan of led.

5.Acidic conditions. Under acidic conditions, LED will be easily affected, so when in acidic conditions we need consider the high level of IP protection.

6.Heat. The temperature around the led .

7.Humidity.The performance of LED also depends on the ambient humidity. Because in humid environments, electronic components, metal parts etc. tend to be quickly damaged and rust, so it’s very important to make the LED system avoid moisture.

Above we mentioned constant current will be good than constant voltage. Here I would like to talk why choosing constant current driving method but not constant voltage driving method.

1. LED nonlinear device, a small change in forward voltage will cause big change at forward current.

Like: LED at 3.3V voltage the current is 20mA, but if the voltage changes into 4.5V, the current will be more than 100mA, expanded 5times, it’s easy to cause burning of led lamp.

2. Like 1W power consumption LED. if forward voltage change 10%(from 3.4V decreasing to 3.1V),which will cause forward current changing from 350mA to 100mA, 3.5times change.

3. Led light output direct ratio with forward current. like following picture, if the forward current declines from 300mA to 100mA, the light output will decline more than 70%.

4,LED display is semi-conductive diode, which has Volt-ampere characteristic. It means that the voltage and current change because of temperature. Like following picture, if using constant voltage, when temperature is up to 85degree, forward current will change from 20mA up to 35-37mA, but the brightness will not increase. When temperature declines into-40degree, forward current declines from 20mA to 8-10mA, and brightness decrease.So we will choose constant current on led display.

That’s the reason why led screens usually adopt constant current driving method .

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