Alas, why do you think the P value measurement of this LED screen is like a blind date? It looks simple, but it’s all a trick when you start! Last year, a shopping mall in Shanghai installed a large screen, and the construction team turned P2.5 into P3. The text showed that it was completely blurred, and it cost 280,000 more to rework. Today, let’s talk about this technical job that seems to be gestured with a ruler, but actually has hidden mystery.

The miscalculation position is equal to the drying

Novice are most likely to fall on the starting line—​​Measure whether the center distance of the lamp beads or the margin distance​? Here is a cold knowledge: the serious scientific name of P value is pixel spacing, and you have to​Adjacent lamp bead luminous center​Start the test.

To give a practical example, when a cinema in Suzhou installed a curved screen, an apprentice took a tape measure to measure the distance between the shells, and the P2 screen forced a P4 effect. Remember the formula:​Tear off the protective film, find the luminous point, and avoid structural adhesive​​, if these three steps are done correctly, the measurement is accurate.

The error difference between tool selection

Don’t believe it, the difference between the vernier caliper and the laser rangefinder can be 15% different! Last year, I helped my friend measure an outdoor screen and used a 20-yuan plastic caliper to measure the P6. When I switched to a micrometer, it was actually P5.8. This 0.2mm gap directly led to the error of the optimal viewing distance of 8 meters. Recommended configuration:

• ​Electronic digital graphics caliper with accuracy ≥0.01mm​(Don't save that 300 yuan)
• ​Range finder with cross laser positioning​(Avoid visual error)
• ​​Highlight flashlight​(Look at the arrangement of lamp beads)

There is an abnormal operation:The diagonal spacing of the quantity is more accurate than that of the horizontal quantity​, especially when encountering lamp beads arranged in plum blossom shapes. When I was helping a gymnasium in Hangzhou to correct, I used this trick to control the error within 0.03mm.

Environmental factors are damaging

Do you think everything will be fine if the quantity in the workshop is accurate? Temperature and humidity will cause trouble. When a northern city installed a screen, P3.91 at -15℃ will heat up to 35℃ in summer and turn into P3.85, causing ripple in the image. Remember these three points:

1. ​20℃±5℃ environment measurement​(The thermal expansion and contraction energy changes by 0.1mm)
2. ​​The screen is powered on for 1 hour​(The size is small in cold screen state)
3. ​Avoid direct sunlight measurement surface​(Hot deformation will cause the value to drift)

To tell me the truth, a project team in Shenzhen took a constant temperature box to the on-site measurement. Although it looked exaggerated, it did reduce the annual volatility to below 0.7%.

Multi-point measurement anti-routine

Don’t believe the nonsense of “sampling three points”! Last year, there was a curved screen in Foshan. The construction party only measured it in the middle area, and the P value of the edge position floated to 5.2mm (nominal P4.8). The correct way to do it is:

• ​​Nine-grid method takes 9 measurement points​
• ​​Exclude maximum and minimum values ​​to average​
• ​​ Pay special attention to both sides of the splicing seam​​

The most exaggerated case I have ever handled is that the P value of the four corners of a second-hand screen can be 0.8mm different, and it makes the entire screen display effect "myopia with reading glasses".

Word game in nominal value

Now some manufacturers have started to play the routine of "±5% error is reasonable". If you calculate it, if the P3 screen reaches +5%, it is actually P3.15. This 0.15mm gap can make the optimal viewing distance from 13 meters to 16 meters. Three tricks to break the situation:

1. ​​The contract states the actual measured value range​​ (such as P3±0.1mm)
2. ​​Request a third-party test report​
3. ​​Bring your own instrument to retest during acceptance​​

A commercial complex in Jiaxing relied on this trick to return all the P4.2 screens that he had originally accepted, saving 17% of the procurement budget.

I have to say that the P value is like taking the pulse of traditional Chinese medicine, and experience is more important than instruments. Now the industry has begun to promote AI measuring instruments, but the old man can still tell the truth with a caliper. Next time, when you see a screen that claims P value, don’t rush to see the parameters. First ask "How do you measure this number?" and keep it and let the person who is loaded with garlic immediately show its true form. Remember, the difference is a slight mistake, and it is not just a joke in the LED display industry!

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