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Display Exam

How Spectroradiometer Exam The Mobile Phone Screen?

Mobile Phone Screen Difference
Mobile Phone Screen Difference

【Question】My friends and I use the same model same brand of mobile phones. His screen is better than my own in terms of brightness and color. I don't know if it is a psychological reason. You can't see this problem alone, but it's obvious when you compare it to each other! Is this due to the OLED screen? Is there such a situation on the LCD screen? What is the reason?

【Answer】Hello there! It's sad that the same mobile phone screen is inconsistent, this problem is indeed ubiquitous. So if the contrast of your mobile phone screen is obvious, it is not a psychological reason. This problem is not only happening with mobile phones, but also with TVs, tablets, and computers. This is the case whether it is an LCD screen or an OLED screen, as shown in the figure below. If you are unfortunate to buy the middle one, you have to contact the after-sales.
When I mentioned this problem, I had to move out a word: panel characteristic. There are no two identical leaves in the world, and even twins have subtle differences in appearance. The same is true for our display or panel. Even a manufacturer produces the same batch of displays, it still has 5~10 nm offset at the peak wavelength which human eye cannot notice easily and it can lead to measurement error!
However, according to the test results, the wavelength has 1 nm offset and might lead to colorimetry(x,y color coordinator) error reaching to 0.0025. If the wavelength shifts to 10 nm, the colorimetry(x,y color coordinator) error will be 0.025. Please refer to the chart below.
This is not finished! The longer a twin grows, the less they look like. If the older brother is often sunbathing, maybe he will eventually be blacker than the younger brother. Not only is the display screen inconsistent, but the performance difference of the color detection instrument and the measurement error can also lead to further widening of the difference between the displays.
Traditional Colormeter optical design uses RGB color filter sensor which simulates colors red, green and blue and estimates the color value which is close to spectral sensitivities of the human eye. However, the following disadvantages remain
1) The value is not objective due to the following:
A. The reflectance or transmittance rate is not included in the calculation.
B. There is no standard observer and perspective.
C. It calculates using RGB alone.
2) The processing of RGB color filter is difficult to control perfectly→The main reason is each RGB color filter sensor cannot perfectly match to CIE1931 XYZ color matching function.
Please refer to the table below. The wavelength shows an error at ±2%→The maximum chroma error value is about 0.0066.
It is precisely because of the characteristics of the panel, coupled with the instrument measurement error in the post-process, it is possible to produce a number of products with poor screen performance in the display of a large number of production. This is why the two phones of the same model have a very different screen performance.
Can this situation be improved?
The answer is yes! Although the congenital insufficiency of the panel characteristics is difficult to change, in the later stages, through the quality inspection of the panel process, in addition to the abnormality of the light color parameter, the abnormality factor can be further analyzed through the “spectral” parameter. Even "Metamerism" cannot be avoided. For most of the luminescent materials, such as "OLED, LED..."; in addition to the quality of the luminescent material, the spectral anomaly also directly affects the specifications of the panel and the performance of the color.
We are constantly exploring a better solution. For example, the UPRtek MK550T Handheld Spectroradiometer uses high-level spectroscopy instead of traditional RGB color separation technology and combines calculation functions to make sure that the spectral sensitivities of x (λ) / y (λ) / z (λ) are comparable to the CIE1931 color matching function.Easily enhance the chroma accuracy and provide measurements result which closer to the human visual function.
In addition, the MK550T spectroradiometer is lightweight, portable, with 3.5 UI colored touchscreen and stand-alone which means it can be operated without computer connection. At the same time, MK550T luminance meter is suitable for various display measurements of LCD, LED, BLU, OLED, MiniLED, microLED that are applied to smart phone, TV, Microdisplay, AR/VR ( Augmented Reality/ Virtual Reality) products and even recommended wearable devices.
So, more manufacturers can use the UPRtek MK550T spectroradiometer to detect on the mobile phone screen, the less chance you will get the poor phone screen. That's what we gonna do.
Note1: This article was co-authored with Hangjianet and published in https://www.hangjianet.com/v5/topicDetail?id=15459612704410000
Note2: Released on 2019/05/10
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