Thursday, June 20, 2013

LED Sign Tech & Spec: Factors Affecting Image Quality on Outdoor Digital Signage

-Scott Hofheins

I’ve been actively evaluating virtually every LED sign I happen to see for quite some time. Its almost an instinctual reaction to immediately determine the manufacturer, quality, size, pitch, etc... This is a common affliction that affects most people in the industry and is a running inside joke.  We are constantly being told (usually by our significant others) to stop looking at the LED signs, and start paying attention to the world around us. Although this may be a long term issue for us, it can be a great temporary issue for those looking to find a high quality LED sign. The aspect I’m going to focus on today is: Why is there variation in the image quality on an LED sign and what are the factors that affect this quality?

The LEDs
An LED display is really just a large group of individual LEDs laid out on a grid, like your computer monitor or TV. Individual LED’s come in many colors, shapes, sizes, configurations and quality. These factors all come into play when dealing with the image on an outdoor digital sign. High quality LED’s that are matched correctly will significantly improve the image displayed.

LED manufacturing is not perfect, and every LED manufacturer must deal with a certain variation of color from LED to LED. The method used to organize LED’s with the same color is typically referred to as “binning”. LED’s with the same color output within a certain tolerance will be put together. This is very important for both  indoor and outdoor digital signage because they are using so many LED’s that if you didn’t bin correctly, the display would look “blotchy” from the different shades of Red, Green or Blue LED’s spread out across the entire unit.

It’s important that the manufacturer address this and can reliably replace LED panels with LED’s in the same “bin grade” as the rest of the sign. You can see this pretty clearly on a display that has one or two squares that are “tinted” against the rest of the sign.  Unfortunately this usually means that the manufacture wasn’t able to provide a matching LED Module (or panel) and the business had to settle for the best of two evils, have a blank square, or a “tinted” square.

Module Construction and Mounting
LED displays are built using groups of LED’s mounted to an LED Module, or panel. These panels will hold multiple LEDs, usually in grids or 8x8 or 16x16 pixels. These modules also house some of the hardware and circuits that control and drive the LED’s on a fundamental level.

The construction of these modules is very important to the quality of the image. Just like mismatched LED’s, modules that are not uniform in construction will create an inconsistent image across the display. This situation will cause a “patchwork” effect, where you can see the individual modules seams, making it look like a patchwork quilt. This may not be noticeable from directly in front of the display, but as you move to the side, you will quickly see the quality difference when lines start appearing out of nowhere.

The module mounting system and cabinet design are also factors manufactures have to consider. A mounting system that doesn’t uniformly pull the LED’s onto the cabinet can cause some of the same effects I mentioned above. The cabinet design must also be consistent. An uneven cabinet will make for an uneven display.

Louver Panel Design
The LED’s must be shaded from direct sunlight.This might sound odd to someone new to the industry, but it is true. Fully exposed LED’s will be washed out by the sunlight and their effectiveness diminished. Louvers are put in place to shade the LED’s from the sun and isolate the light, but not block the visibility of the sign itself. This provides higher contrast by giving the image the blackest surface possible.  

The design of these louvers is important. If the louvers are too small, they won’t shade enough. If they are too big, they might block the view of the LED’s above. The material of the louver panel is also very important. A Flat black non-reflective finish that absorbs the light will improve the contrast and the overall depth of the colors.

Additionally, LED’s in a pixel group (a group of Red, Green and Blue LED’s) will have at least one LED that is physically positioned lower than the rest. Well designed louver panels should shade each LED, not the entire pixel group. Some manufactures are also using “mini” louvers that help divert even more light from the panel surface itself.

Brightness and Contrast
These two principles go hand in hand on a quality display. The display has to be very bright during the day, but it also has to maintain contrast. The blacks must be black, and the whites, white. The contrast is physically determined by the louver face and LED panel design. As I mentioned before, flat black louver panels affect this. The brightness aspect is determined by the LED’s themselves, and how hard they are “driven”. High quality LED’s can be “driven” brighter without a significant loss of life. However, some sub par manufacturers will drive lower quality LED’s harder, and they might be bright at install, but start to fail quite often, over time.

Color Calibration
This relates to the Brightness and Contrast mentioned above, but also includes Color. LED signs need to be calibrated to make sure red is actually red, or chartreuse is actually chartreuse. This is done by calibrating the video signal, and the internal hardware at the factory. Unfortunately there are still manufacturers out there, usually overseas direct, that do a poor job of calibration.The result is an end user with an LED sign that will always look worse than the others around it, regardless of any software adjustments they make.

This is a big one for me, because it is the easiest to control, yet many people don’t realize it’s importance. Good content can make a lower quality sign physically look better than a high quality sign. This is an unfortunate truth that many dealers have felt directly when a customer sees a sign with great content, and decides to use that manufacturer for that reason alone. They are then stuck with a sign that might look great for a couple of months, or maybe a year, but will soon start to fail, over and over again.

Remember, it’s not enough these days to just have an LED sign, it has to look great too. If you're looking into an LED sign, start investigating the ones around you. Note what looks good, and what doesn’t and do your research. Use this blog and the other great resources out there to make sure you get a sign that’s going to look good for a long time. It’s worth the extra effort to really get to know the industry yourself and be an informed buyer.


I hope this post has been informative and helpful. As usual, I welcome ALL constructive comments. Please feel free to comment and add anything I’ve missed, or additional tips you may have regarding this topic. Please visit for many other resources, white papers, and of course: Great looking LED Signs!

**All posts/thoughts/writings are strictly the viewpoint of me and me alone and do not reflect nor speak for Vantage LED’s beliefs, attitudes, thoughts, etc. unless specifically stated.

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