Sourcing LED Displays from China: Pixel Pitch, Brightness and the Specs That Actually Matter
I have bought four LED walls in the last six years, and the first one was a mistake I still hear about. It was a 3.91mm indoor panel quoted at "6,500 nits" by a trading company in Shenzhen. Six weeks after install the leftmost cabinet had two dead pixels per square meter and the buyer blamed me. The specs were technically not lies. They were just written by people who knew I would not read the datasheet carefully. This is the article I wish someone had handed me then.
Pixel pitch is not a quality rating
Pixel pitch is the distance between LED centers, in millimeters. A 2.5mm panel crams pixels closer than a 4mm panel, which is why it looks sharper up close. That is all it means. It tells you nothing about the LED chip brand, the driver IC, the power supply, or how long the thing lasts.
What pitch you actually need comes from viewing distance. The old rule of thumb is minimum viewing distance in meters equals pixel pitch in millimeters, roughly. In practice people sit closer than that and still want it sharp, so I use about 0.8x. For a 3mm panel that means nobody should be closer than 2.4 meters. If your audience walks right past the wall, a 1.5mm panel is the honest answer, and it costs roughly double per square meter. Budget accordingly instead of arguing with the supplier later.
Nits: the number everyone inflates
Indoor panels are honestly rated between 800 and 1,500 nits. Outdoor panels need 5,000 nits and up to beat direct sunlight. Here is the trap. Suppliers quote "peak brightness" measured on a single white module at the factory, often with the current pushed above the safe operating limit, and they call it the panel rating. Five minutes in, thermal derating kicks in and you are at 60% of that number.
Ask for the sustained brightness figure and the derating curve. A supplier who cannot produce a curve in writing is selling you peak numbers. For outdoor work I also ask what happens at 40 degrees Celsius ambient, because a wall that hits 5,000 nits at 25C can drop to 3,500 nits at 40C, which is exactly when the summer sun is worst.
Cabinet sealing and IP rating
Outdoor cabinets live or die on sealing. IP65 on the front face is standard. The rear, where your installer works, is usually the weak point. I look for IP54 minimum on the back and a proper gasket, not a bead of silicone someone squirted on by hand. Ask to see a photo of the gasket channel. Ask whether the cabinet breathes through a vent with a filter or is fully sealed with a pressure equalization valve. Fully sealed with a valve is better in humid coastal cities like Shenzhen and Xiamen, because breathing cabinets pull in moist air at night and condense it inside.
Refresh rate matters more than you think
If your display will ever be on camera, refresh rate is the spec that will embarrass you. A 1,920Hz panel looks fine to the eye and produces rolling black bands on a phone camera recording at 60fps. For broadcast or event work, 3,840Hz is the floor. For anything going on live TV, ask for 7,680Hz and get it in the contract. This is the single most common reason a perfectly good wall looks broken on video.
What I put in the purchase order
- Pixel pitch and exact module dimensions, in millimeters, not "P3 class"
- Sustained brightness at 25C and at 40C ambient, with derating curve attached
- Refresh rate in Hz, minimum, with a sample video shot on a phone as evidence
- LED chip and driver IC brands, written down. Nationstar and Kinglight chips are common references
- Cabinet material, die-cast aluminum is worth the premium over sheet steel for outdoor
- Warranty in years on modules and on power supplies separately
- Spare parts: 2% extra modules, 5% extra power supplies, quoted in the same order
The spare parts line is the one buyers skip and regret. A dead module six months in, replaced by air freight from China, costs more than the 2% spares you should have bought on the same container. Budget for it up front.
Certification reality check
For the EU, look for CE plus the EMC and LVD reports, not just the CE mark sticker. For the US, FCC Part 15 for the controller and UL or ETL for the power supplies. RoHS for the whole assembly. A supplier who shows you a CE certificate with no test report behind it is showing you a piece of paper. Ask for the report number and check the issuing lab.
Where to buy? The cluster is Shenzhen, and the second cluster is in Fujian. Many of the Shenzhen sellers are trading companies reselling from a handful of factories in Bao'an and Longgang. There is nothing wrong with that if they are honest about it, but pricing moves a lot between the trading layer and the factory, so ask who actually welds the modules. See our Shenzhen electronics sourcing guide for how to tell the layers apart.
Final point on price. A 3.91mm indoor panel at a reasonable spec ran around 1,100 to 1,600 RMB per square meter in 2025 depending on chip and driver grade. Outdoor 6.67mm with a proper cabinet sat around 2,000 to 3,000 RMB per square meter. If someone quotes you half of that, they cut something. Find out what.