05 · Backlit lineage
LED & the lamp behind the screen
Here is the thing nobody prints on the box: an LED TV is an LCD TV. The LCD layer cannot make its own light, so it is really a stack of shutters in front of a lamp. That lamp is a wall of LEDs, and there are two main ways to build it. Line the LEDs around the rim and bounce their light across with a plastic guide, and you get an edge-lit screen thin enough to hang like a picture frame. Pack them into a grid right behind the panel, and you get a direct-lit screen that is thicker but lights up far more evenly, and can dim itself in patches for deeper black. Same shutters out front, very different picture, depending on where the light comes from.
LEDs hide along the rim and a plastic light guide spreads their glow across the whole panel. That is how you get a screen thin enough to look like a picture frame. The catch: the light comes from the sides, so the middle can read dimmer and the corners can leak.
Station 01
Two ways to light one panel
Same LCD out front, three ways to put the light behind it. Tap a layout to see where it wins and where it pays for it.
| Trait | Edge-lit | Direct-lit | Full-array |
|---|---|---|---|
| Where the LEDs sit | Around the rim | A grid behind the panel | A dense grid behind the panel |
| Thickness | Slim | Medium | Chunky |
| Even light | Can dim in the middle, leak at corners | Even | Most even |
| Local dimming | Crude, by columns | Usually none | Yes, dozens to hundreds of zones |
| Black in a dark room | Grayish | Grayish | Much deeper |
| Cost | Cheapest | Middle | Priciest LCD backlight |
| You will find it in | Thin budget TVs, laptops, phones | Midrange TVs | High-end LCD and QLED TVs |
Station 02
White light, faked
An LED chip does not glow white. Almost every white LED is a blue chip wearing a coat of yellow phosphor. Drag the coat on and watch the color land on white.
Station 03
The light that leaks
The LCD shutters can never fully block the backlight, so a black screen is where the lamp shows its seams. Pick a layout and dim the room.
Station 04
Local dimming, and the halo it leaves
Split the backlight into zones it can dim on their own and black gets deeper, but a bright object on black bleeds a halo as wide as its zone. Add zones and watch the halo shrink.
The tradeoff
What the backlight buys, and what it can't
An LED backlight is bright, cheap, and lasts for years. It just can never fully get out of the way.
Strengths
- Gets very bright, brighter than OLED can hold across a full white screen, which helps in a sunlit room.
- Cheap and mature, the reason most TVs on a shelf are LED-LCD.
- No burn-in, and the LEDs hold up for many years of use.
Weaknesses
- Black is never truly black, because some backlight always leaks through the shutters.
- Edge-lit panels can show bleed and clouding on dark scenes.
- Local dimming helps, but a bright object on black still blooms a halo unless the zones are tiny.
Questions
LED backlights, quick answers
Is an LED TV different from an LCD TV?
No. An LED TV is an LCD TV. The LCD layer makes the image but no light of its own, so it sits in front of an LED backlight that supplies the brightness. LED just describes the lamp, not the picture layer. Older LCDs used fluorescent tubes for the same job.
Edge-lit or direct-lit, which is better?
For picture quality, full-array direct-lit wins. Its LEDs sit in a grid behind the panel for even light, and it can dim zones on their own for deeper black. Edge-lit is thinner and cheaper, which is why slim and budget sets use it, but it lights less evenly and can leak at the corners.
What is backlight bleed?
Backlight bleed is light from the backlight escaping around the edges or in cloudy patches on a dark screen, because the LCD layer cannot block it completely. It is easiest to spot in a dark room and is usually worst on edge-lit panels. A little is normal; a lot can be a defect.