The rapid pace of advancement in television technology over the past few decades has brought flat, sleek panels with vivid colors and stunning clarity into homes worldwide. But behind all those eye-catching displays lies sophisticated backlighting engineering that makes it all possible. This guide dives deep into the sciences of the different backlight technologies to reveal their inner workings and how they impact the picture you see.
Backlighting – the foundation of the TV image
Modern TVs utilize two primary methods to display images – LCD and OLED. Liquid crystal display (LCD) screens work by modulating a backlight to block and pass through certain amounts of white light. This light then passes through red, green and blue color filters to create the color image. Organic light emitting diode (OLED) screens directly emit light from each individual pixel without requiring a backlight.
Fig. 1 – Edge lighting from sides vs direct lighting covering entire back
For LCD TVs especially, the type and implementation of the backlight technology strongly impacts the final picture quality across criteria like contrast, viewing angles and motion clarity. Backlights have evolved from early CCFL tubes to various configurations of LED lighting driving the LCD panel.
Meanwhile OLED TVs offer the best contrast by directly dimming their self-emissive pixels – no backlight required. But before we crown OLED as king, let‘s analyze the advancements in modern LED backlight technology and see how they stack up.
CCFL backlights – antiquated tech
Early LCD TVs over 15 years ago utilized cold cathode fluorescent lamp (CCFL) backlights. CCFL tubes run a high voltage electrical discharge through an electrically stimulated gas to produce visible light emission. But compared to today‘s LED backlights, CCFL technology had major drawbacks:
- High power consumption
- Large form factor prevented slim TV designs
- Wider color gamuts for HDTV not supported
- Slow response time leading to motion blur
Once LEDs became efficient and affordable enough, they quickly replaced CCFL tubes as the backlight of choice. Modern LED backlights can be categorized by their physical structure behind the LCD panel.
Edge Lit LED backlights
The simplest and most affordable LED backlight design places LED assemblies along the edges of the LCD screen. Light from the LEDs gets directed across the panel with a light guide plate and diffusion sheet.
Pros:
- Very thin display depth possible (~2 cm)
- Low cost to manufacture
- Energy efficient operation
Cons:
- Clouding and uniformity issues in dark scenes
- Narrow effective viewing angles
- Fewer dimming zones limit contrast
Measurements of a 43" edge lit LED LCD TV:
- Contrast ratio – 1100:1
- Peak brightness – 270 nits
- Viewing angle – 160° horizontal
Bottom line: Edge lighting cannot fully illuminate larger panels leading to frustrating light uniformity problems. But for smaller, secondary TVs on a tight budget, edge lit LED gets the job done.
Fig 2. – Comparing edge lit vs full array LED uniformity
Direct Lit LED backlights
By covering the entire rear of the LCD screen with horizontal LED strip lights, direct lit LED backlights can operate brighter while delivering enhanced uniformity:
Pros:
- High total brightness
- Minimal backlight bleed issues
- Wide viewing angles maintained
Cons:
- Increased display depth (~5 cm)
- LED strip lines can cause banding in some scenes
- Limited contrast without local dimming
Measurements for a 55" direct lit LED LCD TV:
- Contrast ratio – 4600:1
- Peak brightness – 550 nits
- Viewing angle – 178° all directions
- Display depth – 5.3 cm
Bottom line: The full LED coverage prevents uniformity problems and pumps out major luminance. But with LEDs always fully on, intra-scene contrast depends fully on the LCD panel rather than backlight.
Full Array LED with local dimming
For the best image quality, modern LCD TVs tend to use full array LED backlights complete with local dimming (LD). This arrangement divides the LEDs into zones then precisely controls each one‘s output. By selectively dimming zones down to total black, far superior contrast emerges compared to edge lit and direct lit approaches.
Pros:
- Excellent contrast with deep blacks
- Great screen uniformity
- High peak brightness over 1000 nits
- Wide viewing angles maintained
Cons:
- Increased display depth (~6 cm)
- More expensive to produce
- Blooming around bright objects in dark scenes
Measurements for a 65" full array local dimming LED LCD TV:
- Contrast ratio – 20,000:1
- Peak brightness – 1400 nits
- Full array local dimming (FALD) zones – 192
- Viewing angle – 178° all directions
- Display depth – 6.2 cm
Bottom line: By independently controlling LED zones across the entire panel, full array local dimming LED backlights unlock superior contrast and High Dynamic Range capability. Dedicated media consumption rooms benefit most from the enhanced depth and shadow detail.
Fig 3. – Full array local dimming (FALD) LED backlights
Mini LED & Micro LED – The future
Just when we thought LED backlights perfected, new shrinking LED die technologies emerge offering orders of magnitude more control. Enter mini LED and micro LED:
Fig 4. – Mini LED and Micro LED shrink down die size dramatically
Mini LED backlights shrink phosphor-coated LED dies down to just 0.2 mm to 1 mm. This permits well over 1000 zones even in 65" and larger TVs for precision dimming control. Contrast and peak brightness can match premium OLED televisions.
Micro LED takes miniaturization even further to less than 0.1 mm LED diodes. But we are still years away from mass producing affordable self-emissive micro LED displays. For now, mini LED delivers stunning full array local dimming performance at the bleeding edge.
OLED – self-emissive pixel perfection
The holy grail display technology for enthusiasts skips LED backlights entirely. OLED uses organic (carbon-based) compounds that directly glow red, green and blue when electrically charged. By combining OLED materials that emit all three primary colors in a multi-layer "sandwich", self-emissive pixels emerge needing no backlight.
And with each OLED pixel operating independently without any light crosstalk between zones, the contrast can be essentially infinite. This makes OLED unmatched for dynamics and realism, especially in dark room viewing.
Pros:
- Perfect black levels and contrast
- Instant response times reduce motion blur
- Excellent off-angle viewing
- Ultrathin panels (~0.5 cm)
- Flexible/bendable options
Cons:
- Peak brightness more limited than LED LCD
- Potential for temporary burn-in
- Currently still expensive
Performance measurements for a flagship 77" OLED TV:
- Infinite contrast ratio
- Peak brightness – 820 nits
- Per-pixel local dimming
- Viewing angle – 178° all directions
- Panel depth – 0.45 cm
Bottom line: If your movie nights demand inky shadows and eye-popping contrast for a premium cinematic experience, OLED rules the roost. The self-emissive pixels switch off completely to achieve perfect pixel-level blackness.
Head to head performance comparisons
Now that we analyzed the panel architectures and underlying operation of each backlight technology, let‘s stack them up against key picture quality criteria:
Contrast ratio
| Backlight type | Native contrast | Real scene contrast |
|---|---|---|
| Edge lit LED | 1100:1 | 3000:1 |
| Direct lit LED | 4600:1 | 5000:1 |
| Full array LED w/ FALD | 20,000:1 | 50,000:1 |
| Mini LED w/ FALD | 1,000,000:1 | 100,000:1 |
| OLED | Infinite | Infinite |
Table 1. Measured contrast ratio across backlight technologies
The zones of local dimming allow LED LCD contrast to approach OLED levels. But no LED backlight can fully extinguish pixels like OLED can.
Peak brightness
Higher peak brightness expands the contrast, fights room glare and boosts pop in HDR content.
| Backlight type | Peak brightness (nits) |
|---|---|
| Edge lit LED | 270 nits |
| Direct lit LED | 550 nits |
| Full array LED w/ FALD | 1400 nits |
| Mini LED w/ FALD | 2000 nits |
| OLED | 820 nits |
Table 2. Measure peak luminance across backlight types
FALD LED backlights can far outshine OLED, but dark scene detail still falls short.
Color volume
Combining color gamut coverage and luminance yields an overall color volume score – higher is better.
| Backlight type | % DCI-P3 coverage | % Rec. 2020 coverage | Color Volume |
|---|---|---|---|
| Edge lit LED | 90% | 69% | 258,117 |
| Direct lit LED | 93% | 71% | 389,544 |
| Full array LED w/ FALD | 96% | 75% | 703,185 |
| Mini LED w/ FALD | 98% | 81% | 1,015,829 |
| OLED | 97% | 86% | 719,765 |
Table 3. Color performance metrics across backlight technologies
Quantum dot filters placed over LED backlights continue to enhance color performance. But OLED pixels directly emit desired wavelengths.
Real-world TV model comparison
Let‘s examine how this tech manifests across a 65" LCD TV with three different LED backlight systems:
Entry-level edge lit: TCL 65S535
- Contrast ratio: 7000:1
- Peak brightness: 350 nits
- Local dimming zones: 12
- Inputs: 4 HDMI 2.0
Mid-range full array: Sony X90K
- Contrast ratio: 14,000:1
- Peak brightness: 730 nits
- Local dimming zones: 32
- Inputs: 2 HDMI 2.1
Flagship mini LED: Samsung QN90B
- Contrast ratio: 383,000:1
- Peak brightness: 2000 nits
- Local dimming zones: 792
- Inputs: 4 HDMI 2.1
Review measurements confirm the mini LED Samsung delivering contrast and peak luminance in a class above thanks to the sheer zone density. But the Sony full array model still impresses for under $1500.
The best backlight for your next TV
For shoppers seeking:
- Visual pop – Favor full array or mini LED for high peak brightness
- Cinematic realism – OLED rules with infinite contrast
- Sports motion – Full array and mini LED offer 120 Hz gaming
- Bright room usage – Direct lit LED cuts through glare well
- Console gaming – Mini LED has HDMI 2.1 and VRR support
- Streaming box TV – Edge lit LED fits budgets under $500
In 2023, full array local dimming LED represents the performance sweet spot. Contrast, color and motion all impress without breaking budgets. We are also on the cusp of mini LED delivering stunning results more affordably. Meanwhile OLED remains the picture quality champ focused on contrast over peak luminance.
Understanding your room lighting and viewing priorities helps narrow the myriad backlight technologies down to a few great options. And remembering that the LED backlight directly enables the LCD image allows buyers to focus on contrast, brightness and dimming capabilities during research. So savvy shoppers should ignore pure panel specs and model names, peering behind the display at the backlight within. This holds the real key to your next TV fulfilling your needs.
