Our eyes are easily attracted to a contrast of rich and deep colors. This is most often the goal when designing LED displays. But achieving a perfect outcome does not happen always. A fantastic-looking display is produced by matching the capabilities of human eye with the kind of technology that can take advantage of those capabilities. In this context, a few essential characteristics to keep in mind are:
- Vision capability
- Solution to ambient lighting
- Optical filters
The main characteristic for producing a great LED display is to consider how dark regions of the content are reproduced, keeping in mind the ambient lighting. ‘Brightness contrast’ is a term that describes how different the darkest and brightest regions of the display are, and is usually expressed as a ratio. When measuring this contrast ratio, it is important to keep in mind that every display will be operating in some sort of background lighting conditions. Hence the environment of the display should be considered in every situation.
Another factor to consider is the total range of colors that can be produced on the LED screen. This range is equal to the ability of displaying deeply saturated primary colors such as red, yellow, green and blue. Equal importance should be given to color saturation as well as the white areas of the display. Careful colorimetric engineering is needed to correctly obtain both these attributes.
The general rule of thumb is that high contrast will present attention grabbing and visually appealing images while low contrast may seem dull and may signify less important information. The visual system of a human being is a mixture of perception, sensitivity, adaptation, acuity, aging effects, day vs. night and so on. An interesting fact is that humans do not perceive brightness on absolute scale. Instead, they judge it based on other things within immediate attention.
In the above image you may notice that the left side of the stripe in the middle is brighter than the right side. In reality, the stripe is the same color throughout but because of the surrounding colors, the stripe appears brighter on one side and dull on the other. This is an example of relative brightness perception to prove that contrast affects the ability to notice details in an image. In other words, increasingly larger steps of actual brightness are needed to realize equal steps of perceived brightness.
Solution to Ambient Lighting
Ambient lighting is the biggest enemy for an LED display with high contrast images. The reflections of ambient lighting restrict the blackness and increase the noise for a display. Furthermore, the color range of the display will be compromised due to the reflections from surrounding light.
Specular reflections are mirror-like reflections that can affect day and night time operation of an LED screen. Diffuse reflections are scatter like reflections that appear from objects and light sources. The effects of specular reflection are dependent on viewing angles while diffuse reflections do not depend on angles so much.
Relatively modest contrast ratios would suffice for producing attractive content. Solar light reflecting a display is the biggest challenge for obtaining sufficient contrast ratios. In evaluating display brightness, look out for diffuse reflectance that does not exceed 0.4%.
Infra red (IR) and Ultra Violet (UV) filters are often used to restrict solar heat absorption but these have an adverse effect on the image quality of the LED display. Creating IR and UV filters that do not affect image quality is very difficult. This is because these filters produce an unnatural tint on images that makes them easily visible because of the way they shift colors of the image as if it were a function of the viewing angle. Also, these filters have a reflecting mirror-like appearance that is hard to miss.
One would then wonder why manufacturers use such filters on LED screens. Probably out of desperation! Buyers want LED panels that can withstand high temperatures, has a well functioning thermal design, and can reduce UV damage. When incorporating all these features, the color reproduction and luminance of the LED screen has to be compromised.
In conclusion, a fantastic looking display is one that is titled so by humans viewing it. The interaction between human eye and the LED display is where the mindset for a great looking display begins. Further characteristics such as location and environment will also play a role. Therefore, when aiming to design a fantastic looking LED display, the key is to consider the environment in which the screen will be operating and then think about how the human eye will perceive it.