EL backlight is an obsolete technology, it is disappearing. CCFL backlight is disappearing, too. They are both being replaced by LED Backlight. I have never heard anyone ask for a quote about CCFL backlight. But every now and then, I can hear my customers ask about EL backlight, so let us dig in and find out “What is EL backlight?” and “Why EL backlight still has market demand?”
Our first question: What is EL backlight?
EL is abbreviation for ELECTRO LUMINESCENT which is a type of flat cold light. The luminous principle of EL Backlight is that two pieces of paper plates which sandwich the phosphor are driven by the high voltage and the phosphor is emitting light because of the high voltage. The brightness depends on the magnitude of the voltage and the frequency of the alternating current. Within the range of 30V ~ 250V, the higher the voltage, the brighter the EL backlight. However, although the higher voltage can make the EL backlight brighter, excessive voltage will directly and seriously affects the using time of EL backlight and we strongly suggest that the voltage should not exceed 140v under normal circumstances. Within the range of 50Hz ~ 2000Hz, the brightness will increase with the increasing of the frequency of alternating current. Certainly, the frequency is another important factor in determining the using time of EL backlight. It is considered that in general the frequency should not exceed 2000Hz. By the way, the using time of EL backlight is that the time span from the initial luminance to the half luminance. If it is calculated by hours, the using time of EL backlight is more than 10,000 hours theoretically. Working temperature is the most important factor affecting the using time. It can make the brightness rapidly decrease until the complete loss of light. Therefore, a good environment and working condition is the premise of long-term using of EL backlight.
The Feature of EL Backlight
◆ It has a wide visual angle and it is a flat and solid state light emitting source.
◆ It is super thin, which is as thin as 0.12mm.
◆ It is extremely lightweight.
◆ It has rich and luminous colors.
◆ It can be bent and the bending radius can reach 5cm.
◆ It has a strong resistance of shock and impact.
◆ It is a low power consumption light source.
◆ It is a cold light source that generates no heat. It is considered that more than 97% of the electrical energy is converted into the light energy.
◆ It has a long using time.
◆ It is easy to be processed into arbitrary shapes.
◆ No ultraviolet is generated.
◆ It has high visibility when it is in a foggy condition.
◆ The light is soft and evenly and will never hurt your eyes.
◆ It is good waterproof and it can emit light under the water.
◆ Operating Voltage: 30V ~ 250V.
◆ Operating temperature: -35℃ ~ +60℃.
◆ It can be driven by voltage transformer or IC.
The Main Technical Parameters of EL Backlight
1. Operating voltage range: 30V ~ 220V. Optimum operating voltage: 120V.
2. Operating frequency range: 50Hz ~ 5000Hz. Optimum operating frequency: 1500Hz ~ 2000Hz.
3. Static capacitance: 6nF/m (20℃, RH<80%).
4. Brightness is 30cd / m2 ~ 126cd/m2 under the working conditions: Voltage: 120V, frequency: 200Hz ~ 2000Hz.
5. Power Consumption is 108mW/m ~ 1032mW/m under the working conditions: Voltage: 120V, frequency: 200Hz ~ 2000Hz.
6. Using time is about 8,000 hours under the working conditions: Voltage: 100V, frequency: 400Hz, normal temperature and humidity.
7. Continuous working temperature / Relative humidity: -20℃ ~ + 70℃; RH<90%.
8. Storage Temperature / Relative Humidity: -10℃ ~ + 40℃; RH<65%.
9. The Main Wire Size: φ0.9, φ1.3, φ2.3, φ3.2, φ4.3, φ5.0.
10. The primary colors: red, yellow, blue, green, orange, purple, pink and white.
Here is our second question: Why EL backlight still has market demand?
I think I have already given you the answer. We can see that among all the light sources of backlight, EL backlight is the thinnest one. I am sure that the trend of LED backlight is becoming super thin and lightweight. I have made the thinnest LED backlight for one of my clients. The light guide plate is as thin as 0.6 mm, but it is the best we can do. The total thickness of LED backlight is 0.9 mm. You may not know that it caused lots of troubles for us. 0.6 mm is too thin to install SMD LED into PCB in the traditional way. The minimum thickness of PCB to install SMD is 1.0 mm, so we have to make a dedicated FPC for it.
EL backlight can be made as thin as 0.12 mm. No wonder why it is popular in a world where people pursuit super thin and regard the thinner the better as aesthetical standard.
Although EL backlight has so many “virtues”, LED Backlight is replacing EL backlight that is beyond all doubts.
◆ Brightness. There is no way we can use EL backlight as a lamp for illumination. It is too dim to be used as a light source. As we know, LED backlight can be divided into edge LED backlight and bottom LED backlight. Theoretically, we can install as many SMD LEDs as we want.
Take edge LED backlight for example. If two edges are installed with SMD LEDs , it is not bright enough, we can install 4 edges with SMD LEDs. Please see the picture above. Generally, the pitch between two SMD LEDs is 8.0 mm-15.0 mm. If 4 edges with SMD LEDs are not bright enough, we can make the pitch 6.0 mm to increase the numbers of SMD LEDs.
Even if you still think it is not bright enough, we can double the SMD LEDs or even triple the SMD LEDs by increasing the thickness of light guide plate from 3.0 mm to 6.0 mm and 9.0 mm.
Then the brightness will be double or triple. Please see the picture above. I admit that is insane. It is too expensive. Usually, edge LED backlight with two edges which are installed with SMD LEDs is more than enough in the brightness.
I never suggest my customers using bottom LED backlight under normal circumstances because of the cost. But the bottom LED backlight is much brighter. See the picture below.
Generally, the pitch between two SMD LEDs is 20.0 mm. But we can make it 10.0 mm, even 5.0 mm, so we can make the numbers of SMD LEDs double or fourfold.
This is crazy. It will be incredibly expensive. We have never made the pitch 5.0 mm bottom LED backlight for any of my customers before. I just want to tell you it is possible that we can increase the brightness of LED backlight.
It is very difficult to increase the brightness of EL backlight. Generally, EL backlight is much dimmer than LED backlight.
◆ Color. EL backlight usually only has one color which is white. And LED backlight is much better in color saturation and color variousness. See the advantages of LED backlight.
You may have seen EL backlight which has displayed several colors at the same time.
Actually, we print all the colors we want on the diffusion film and use white light as light source. See the picture above, we print purple, yellow, red, orange, pink on the diffusion film and use the black light proof paper to cover the part we don’t want to emit light. Finally, we use an electronic controller to control the display, which we need to input the control program in the control IC.
This is a RGB LED backlight which has 8 colors. We only use RGB SMD to make it happen. Theoretically, we can make almost any color with RGB lamp.
◆ Using time
Theoretically, the using time of LED backlight is 100,000 hours and the using time of EL backlight is 10,000 hours. But practically, the using time of LED backlight is 20,000~30,000 hours and the using time of EL backlight is 2000~3000 hours. The practically using time is determined by so many factors and there is a huge difference in each individual.
◆ Driving voltage
LED backlight is driven by low voltage and EL backlight is driven by high voltage.
The driving voltage of white LED lamp is 2.7v ~ 3.4v. Because large LED backlight has so many LED lamps, we can have to use Serial and Parallel Hybrid Connection for LED lamps.
3 LED lamps and 1 electronic resistor are serially connected as one group. The driving voltage is 12V. I am not here to talk about the benefit of LED Serial and Parallel Hybrid Connection.
The output voltage of portable battery is usually 3.0 v~4.5 v, so it can generate LED backlight.
Meanwhile, the driving voltage of EL backlight is from 30V ~ 250V. By the way, direct current of portable batteries can generate EL backlight too. But it usually needs an exterior battery voltage booster. Please see the picture below.