Bright, brighter, brightest? Why a display backlight system is more than meets the eye
Let there be light!
If only it was that simple in the world of display backlight systems.
The human eye doesn’t perceive light in a linear way. So, if you’re looking to achieve a super-bright result, your display will need a huge amount of energy – in fact, more than double the cost of a standard display. For energy critical devices, this often means compromising brightness for battery life.
But sometimes displays must shine brightly when used. In direct sunlight, for example, or under the glaring lights of a hospital emergency room. But extreme light comes at a cost in many ways: Financially, in energy usage, lifespan, thermal dissipation and, it may surprise you, in terms of coloration.
Shooting more light through a TFT cell will wash the colors out, so even the cell itself needs to be modified to convert a dim display to a sun-defeating lantern that is still capable of showing saturated colors. High-performance LEDs can also help to reduce heat, but additional passive cooling techniques are still often required.
Proper backlighting is complex even in advanced edge or back lit arrangements, where LEDs are arranged in a line (edge lit) or array (back lit). The LEDs form miniature points of super bright light and subsequently take on the characteristic of a spotlight. Therefore, a system of light shaping elements is needed to convert the multiple tiny dots into a uniform area of light.
The end goal is high brightness, low heat dissipation and the correct white point. Which, in and of itself, is not straightforward. A proper mix of wavelengths is required to ensure a wide color space for the emitted picture, because what is considered ‘white’ in one context may not necessarily be the same as ‘white’ in another. Adding to the challenge is that the whole backlight system must be as thin as possible.
All these considerations for just one function?
When we describe all the challenges of backlighting this way, it may sound impossible to get it right, but we do –again and again, millions of times with the best results. We know and understand just how important each of these elements is for application designers. The selection of proper display brightness, and in some cases even the correct customization of a display backlight is mission critical and may well result in the failure or success of the final product.