Common LED module are divided by the "P" number indicates the distance between each of the LED in the module in mm.
The "P" number can also use it as a indicator as the recommended viewing distance.
For example, a P3 LED module has a recommended viewing distance of 3 meter.
As of today, the most commonly use modules are P: 1.67, 2, 2.5, 3, 4, 5, 8, 10.
For outdoor purposes, P: 5-10 are recommended due to a potential bigger display area for outdoor and longer viewing distance.
For indoor purpose, P: 2-4 are are recommended due the a potential smaller display area for indoor and shorter viewing distance.