One of the aspects people look to in order to judge the quality of an LED display is how bright it is. Brightness as an indicator of quality can be overrated a bit. If a display is bright enough to be seen in daylight then it is doing its job. People have become sensitive to brightness levels because of the introduction of some low quality imported displays that actually aren’t bright enough to be seen when the sun is out!
There are two units of measure that are primarily used to express the brightness of a display. The first is “Nits” and the second is “CD per square meter”. Both are a measurement of luminescence. In fact, they are precisely equal to one another (1 nit = 1 cd per square meter). The “cd” stands for candela. In the US, we tend to refer to brightness in terms of “nits” probably because of our fear of all things metric. In the case of outdoor LED displays, typically a user would want a display which is at least 4000 nits depending on how much sunlight it was going to be exposed to. Some single color displays have trouble meeting this brightness level if they are foreign imports but almost all full color displays would have no trouble. That’s due to the fact that full color displays use more diodes in each pixel and can therefore shine brighter than a single color. Sticking to US based manufacturers is always a sure way to assure yourself that your display will be bright enough.
To go deeper into how brightness is determined, we need to examine how “luminescence” is defined. Luminescence is determined by a derivative of luminous flux, and the angle and area of the luminous source. In other words, it is a reflection of how much luminous power your eye would detect from looking at a given surface from a given angle. It is a measurement of how bright that surface would appear. To put this definition to use with an interesting example, the sun at noon, is about 1.6 X 10^9 nits! The computer screen that you’re looking at right now to read this article is emitting about 50 to 300 nits depending on what your brightness setting is.