If you are still complaining about that your LED
There are basically two stages where the brightness can be improved. The first one is during the production of LEDs and the latter is when you already have your signs.
During the production process or so called encapsulation process, the luminance can be enhanced by improving the luminescence efficiency of the LED chip's active layer or changing the chips' shape or size to achieve a better luminous quality. If you haven't bought your sign, it's always a good idea to consult the supplier about the chips and check out the luminance test report to make sure the chips that they will use are bright enough for your sign.
However, there are lots of cases that you already got your LED outdoor displays but don't think they are not as bright as you expected when you are testing them in the field. Actually you can try 3 methods to enhance it.
1. Change the current that is running through your LED display. Generally speaking, LEDs allow a 20 milliampere working current continuously. But only red LED has saturation phenomenon, other LEDs' (Blue and Green) luminance is in ratio with the current amount that runs through them. A higher but safe current will make your sign much brighter.
2. Adjust the brightness from the controlling system. Yes, it is adjustable. Normally if you find that the brightness of your sign seems to be lower than the data you got from your supplier, it means probably they decreased it before shipping it to you to save more energy. Your supplier should be able to teach you how to make it brighter step by step or their engineer can just do it for you. As the matter of fact, adding another multifunction card is a very good idea to help you do it automatically and a lot of controlling systems makers are producing it too. It will adjust the luminance of your display based on the brightness of the environment as well as some other additional functions such as auto switch, temperature probe, etc.