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Experiment on OLED display brightness decay by suffering UV damage

The Ultra-violet (UV) light has a shorter wavelength and greater energy than visible light. If human beings expose to high-intensity UV light, which will damage the human body. Organic materials in OLED displays also suffer UV damage.

 

The Electromagnetic Spectrum

 

It is common to use UV index to define the intensity of UV, which is an international standard measurement of the strength of the sunburn-producing ultraviolet (UV) radiation at a particular place and time.

 

UV index Media graphic color Risk of harm from unprotected sun exposure, for the average adult Recommended protection
0 to 2 Green "Low" A UV index reading of 0 to 2 means low danger from the Sun's UV rays for the average person. Wear sunglasses on bright days. If you burn easily, cover up and use broad spectrum SPF 15+ sunscreen. Bright surfaces, sand, water, and snow, will increase UV exposure.
3 to 5 Yellow "Moderate" A UV index reading of 3 to 5 means moderate risk of harm from unprotected sun exposure. Stay in shade near midday when the Sun is strongest. If outdoors, wear sun-protective clothing, a wide-brimmed hat, and UV-blocking sunglasses. Generously apply broad spectrum SPF 15+ sunscreen every 1.5 hours, even on cloudy days, and after swimming or sweating. Bright surfaces, such as sand, water, and snow, will increase UV exposure.
6 to 7 Orange "High" A UV index reading of 6 to 7 means high risk of harm from unprotected sun exposure. Protection against skin and eye damage is needed. Reduce time in the sun between 10 a.m. and 4 p.m. If outdoors, seek shade and wear sun-protective clothing, a wide-brimmed hat, and UV-blocking sunglasses. Generously apply broad spectrum SPF 15+ sunscreen every 1.5 hours, even on cloudy days, and after swimming or sweating. Bright surfaces, such as sand, water, and snow, will increase UV exposure.
8 to 10 Red "Very high" A UV index reading of 8 to 10 means very high risk of harm from unprotected sun exposure. Take extra precautions because unprotected skin and eyes will be damaged and can burn quickly. Minimize sun exposure between 10 a.m. and 4 p.m. If outdoors, seek shade and wear sun-protective clothing, a wide-brimmed hat, and UV-blocking sunglasses. Generously apply broad spectrum SPF 15+ sunscreen every 1.5 hours, even on cloudy days, and after swimming or sweating. Bright surfaces, such as sand, water, and snow, will increase UV exposure.
11+ Violet "Extreme" A UV index reading of 11 or more means extreme risk of harm from unprotected sun exposure. Take all precautions because unprotected skin and eyes can burn in minutes. Try to avoid sun exposure between 10 a.m. and 4 p.m. If outdoors, seek shade and wear sun-protective clothing, a wide-brimmed hat, and UV-blocking sunglasses. Generously apply broad spectrum SPF 15+ sunscreen every 1.5 hours, even on cloudy days, and after swimming or sweating. Bright surfaces, such as sand, water, and snow, will increase UV exposure.

 

The emitting layer made by organic material is the key factor behind the light emission of OLED displays. High-intensity energy can damage the structure of organic material in the emissive layer, and the device will suffer from low light-emitting efficiency and fast brightness decay.

In order to protect the organic material from UV damage, we have to minimize the intensity of UV wavelength. Meanwhile, we don’t want to decrease the intensity in the visible light range(400nm~700nm). For this purpose, polarizers are very suitable.

 

Transmissioin for Visible Polarizer

 

To find out the polarizer’s ability of UV protection, we designed an experiment using a polarizer. Polarizer covered the half area of the OLED panel, and the remaining area was not covered. Then we kept the OLED panel inside a UV chamber and measured the brightness of both areas of the panel. We recorded the brightness decay ratio under UV expose. Please check the following figure, the blue line data is the area covered by the polarizer, the brightness has been decayed 0.76% after suffering energy which equals to 1 UVI intensity expose 450 hours, and the red line is the area without any cover, the brightness has been decayed 4.97% at the same time. Without polarizer protection , the brightness decay ratio is about 6.5 times faster than the area with polarizer coverd.

 

1UVI intensity exposure time

 

We’d like to calculate the lifetime that brightness of OLED display decay to 50% exposed by different UV intensity. The environmental conditions are supposed as follows, we suppose all day in a year is a sunny day, and the total UV energy in one day is equivalent to 4 hours midday UV intensity expose.

In this case, the estimating lifetime of OLED displays that are exposed by different UV intensity levels showing below. It shows the ability to protect OLED displays from UV exposure. With Polarizer covered, the lifetime is 3 times longer than without being covered In a high UV intensity environment (6UVI).

 

  Exposure
intensity 
1UVI
+naturally decay
2UVI
+naturally decay
3UVI
+naturally decay
4UVI
+naturally decay
5UVI
+naturally decay
6UVI
+naturally decay

With
polarizer

How long brightness decay to 50% 749 days 680 days 623 days 575 days 533 days 497 days
w/o
polarizer
How long brightness decay to 50% 481 days 338 days 260 days 212 days 179 days 154 days
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