LCD backlighting in laptops
LCD backlighting in laptops
This is my second article on this theme. Here I will share with some more knowledge that I got recently from the net. The first article gives basic understanding what is meant by word “backlighting”, so I’ll try be short and focus only on things that were missed or covered not so clear.
LCD (Liquid Crystal Displays) are not emissive – they don’t have a light. This is why LCD displays must have som kind of backlighting we could see the colors and clear image. This is the essence understanding displays. No matter where is built in cell phone, laptop or tv all displays has it in common.
All displays has the following 3 items:
1. Light source – CCFL or LED lamps.
2. Light guide (diffusion) panel that diffuses light from the light source equally through all surface. I’m not 100% sure is it must for direct-lit type displays, but for edge-lit for sure.
3. LCD panel.
There are 2 main types of backlighting by light source placement:
1. Edge lightning – the light source placed in the edges of panel, not behind.
2. Direct lightning – the light source placed behind panel (in LED arrays, or few CCFL lamps).
Edge lightning approach makes display much thinner and durable so all displays in laptops are made using this kind of construction.
Edge-Lit Line Source (CCFL) with Light-guide:
Edge-lit with LED:
As you see, the construction basically is the same. Just instead of CCFL lamp placed few LEDs. Usually it is on one or 2 edges. Light source in two edges gives more brightness comparing with one edge but consumes more power.
Direct lighting construction examples:
I’m sure such construction is not for laptops. It creates more brightness, but consumes more power, construction is heavier and thicker.
Here I covered only main concept of understanding what is behind LCD. It is clear that edge-lit approach has many advantages over direct one. Developing light-guide technology plays very important role there. It has its limits and large size TV’s still cannot use it.
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