LCD backlight units (BLU) for TFT and LCD modules · Edge-lit and direct-lit layouts, LED light bar, light-guide plate and dot pattern, reflector, diffuser and prism sheets, luminance, LED current and voltage, constant-current drive, lifetime to half brightness and temperature derating
A backlight assembly (backlight unit, BLU) is the light source behind a transmissive LCD panel: LEDs (or, in older designs, fluorescent lamps) whose light is spread into an even sheet by a light-guide plate or diffuser, redirected toward the viewer by prism films and recycled by a reflector, so that the liquid crystal can modulate it into an image. Ask three things first: what panel size, active area and luminance the display needs, how the LEDs will be driven (current, voltage, constant-current driver, dimming) and what lifetime and temperature range the product must meet.
Backlight units for LCD panels and modules: edge-lit and direct-lit LED backlights with their light bars, light-guide plates, optical films, reflectors and frames, supplied separately or as part of an LCD module. Complete LCD modules, LED driver ICs, OLED and other self-emissive displays and general LED lighting panels are outside this page except where compared.
01
A patent assigned to LG Display classifies LCD backlights as direct-type or edge-type according to where the light source sits, and lists electroluminescent, LED, CCFL and HCFL light sources. In the edge-type unit it describes, a first and second prism sheet and a light-diffusion sheet lie over a light-guide plate with a reflector below; the lamp sits at the side of the plate, and the plate — PMMA, chosen for its light transmittance — acts as a waveguide that turns the edge light into a plate-type source. [1]
To make the output even, a light-diffusing substance is printed on the lower face of the plate in dots whose size grows with distance from the lamp: small dots near the lamp, larger ones further away. The diffusion sheet (PET or PC with a particle coating) spreads the light for uniform luminance with viewing angle; the two prism sheets pass light within a range of angles and totally reflect the rest back down to the reflector — a reflective metal coating on PET or PC film — so that frontal luminance rises. The assembly is held in a mould frame, with a top case and bottom cover protecting the backlight and panel. [1]
Editorial note: the patent describes a CCFL edge-type unit as its related art; current LED backlights replace the lamp with an LED light bar at the plate edge (edge-lit) or an LED array behind a diffuser (direct-lit). Ask the supplier which layout, plate material and film stack are offered for your thickness and brightness.
Give the supplier the panel model or active area and outline, module thickness limit, required luminance and uniformity, colour temperature or chromaticity, edge-lit or direct-lit preference, number and position of LEDs, film stack, connector or FPC, operating and storage temperatures, and quantities.
02
Ampire's data sheet for the AM-480272MGTZQW-00H 4.3-inch TFT module (480 × 272 pixels, 95.04 × 53.856 mm active area, 105.5 × 67.2 × 2.9 mm module) describes an edge-lighting white-LED backlight with 12 LEDs. It lists LED current 40 mA (typ.) and 50 mA maximum, LED voltage 16.2–19.2 V, and luminance of 400 cd/m² minimum and 500 cd/m² (typ.) at 40 mA and 25 °C, measured at the panel centre with a 1° luminance meter after 10 minutes' operation. [2]
It rates operating LED life at 40,000 h minimum and 50,000 h (typ.), defined as the time until module brightness falls to 50% of its original value at 25 °C and 40 mA, and warns that life can be shorter if current exceeds 40 mA. [2] It calls for a constant-current source to drive the white-LED backlight and says that above 60 °C (panel surface) the LED current should be reduced to 30 mA maximum. [2] The data sheet labels this 60 °C as the panel surface temperature in one place and as the ambient temperature in another; confirm with Ampire which one applies before selection. [2]
Editorial calculation: at 40 mA (typ.) and the listed 16.2–19.2 V, the backlight draws about 0.040 × 16.2 ≈ 0.65 W to 0.040 × 19.2 ≈ 0.77 W, assuming the 40 mA is the total backlight current at the listed voltage; and 50,000 h (typ.) of continuous operation is about 50,000 ÷ 8,760 ≈ 5.7 years to half brightness. [2] Ask the supplier for the LED string arrangement and the life figure at your actual current and temperature.
03
3M's application guide for its Brightness Enhancement Film (BEF, January 2020) explains that the prismatic structure refracts usable light toward the viewer and reflects the rest back into the display for recycling, raising on-axis brightness by compressing light into a narrower viewing angle. One sheet, or two sheets crossed at 90°, can be used, and a reflective polariser film (3M DBEF) goes on top, closest to the LC module. [3]
The guide says prisms must face the LC module and away from the backlight; the viewing angle is compressed in the plane at 90° to the prism direction, with only slight compression in the other plane, and a second sheet must be crossed at 90° to compress both planes. Films should be left free-floating to avoid warping or buckling, or tacked along one edge or at two adjacent corners with double-coated tape, and assembled in a clean area at 10–30 °C and 35–65% relative humidity. [3] The stack order matches the prism sheets in the patent described above. [1]
Editorial calculation: replacing two 155 µm BEF2/BEF3 sheets with two 90 µm BEF4 sheets saves about 130 µm of stack height.
| 3M BEF film | Applied thickness (excluding liners) | Delivered thickness | Note from the guide |
|---|---|---|---|
| BEF2-T-155n | 150 µm | 230 µm | Non-halogenated acrylic prisms on polyester; features to avoid wet-out |
| BEF3-T-155n | 155 µm | 235 µm | Randomised prism pattern; slightly lower gain than BEF2 |
| BEF3-M2-155n | 154 µm | 234 µm | Matte version; softer brightness fall-off, may remove a separate diffuser |
| BEF4-GT-90 (24) | 90 µm | 170 µm | Thinner, higher-gain resin; for moiré avoidance |
State the backlight thickness budget, required on-axis luminance and viewing angle in each plane, and ask which prism and reflective polariser films the stack uses, their orientation and how they are fixed.
04
A 2025 open-access study in Polymers made prism films by imprinting UV-curable resin on 188 µm primer-treated PET from a master with grooves 50 µm wide and 25 µm high, and tested them on a 100 mm × 100 mm prototype edge-lit LED backlight (light-guide plate, diffuser films and LED source) with a luminance colorimeter at 100 cm in a dark room. The replicated film had a 5–8 µm base layer, prism peaks 24–26 µm high and peak bases 48–49 µm long. [4]
Adding a high-refractive-index thiol monomer raised the cured resin's refractive index from 1.564 without thiol to 1.574 at 30 phr, and at 30 phr the backlight luminance was 3.96% higher than with the thiol-free resin, with stable colour coordinates. Volume shrinkage fell from 6.55% to 2.40% as thiol content rose from 5 to 30 phr, and the thiol-free coating delaminated by more than 65% on bare PET (adhesion 0 B). [4]
Editorial calculation: grooves 50 µm wide and 25 µm high give a 90° apex angle (2 × arctan(25 ÷ 25)). The study shows that a refractive-index change of 0.010 moved luminance by about 4% on one backlight, so a supplier substituting prism film or resin should show a luminance measurement on your backlight, not only the film data sheet. [4]
| Prism film item (Polymers, 2025) | Value |
|---|---|
| Substrate | 188 µm PET, primer-treated [4] |
| Master groove width / height | 50 µm / 25 µm [4] |
| Replicated peak height / base | 24–26 µm / 48–49 µm [4] |
| Cured resin refractive index | 1.564 (no thiol) to 1.574 (30 phr) [4] |
| Luminance change at 30 phr thiol | +3.96% [4] |
| Volume shrinkage | 6.55% (5 phr) to 2.40% (30 phr) [4] |
05
Sanbum Optoelectronics lists backlight modules for these display classes; ask it for the LED current, hours to 50% brightness and film stack covered in the sections above.
06
The optical rows follow the edge-type stack in the LG Display patent; the LED bar and connector rows also draw on the Ampire module data.
| Part | Role | Fix in the order |
|---|---|---|
| LED light bar or lamp | Provides the light at the edge or behind. [2] [1] | LED count, colour, current. |
| Light-guide plate | Spreads edge light into a sheet. [1] | Material (PMMA), thickness, dot pattern. |
| Reflector | Returns light toward the panel. [1] | Film material and coating. |
| Diffusion sheet | Evens luminance across angles. [1] | PET or PC, haze. |
| Prism sheets | Raise frontal luminance. [1] | Number and orientation. |
| Frame and covers | Hold and protect the stack. [1] | Mould frame, case, bottom cover. |
| Connector and driver interface | Supply LED current. [2] | Anode/cathode pins, constant current. |
07
Apart from the film row (3M guide), the published values here come from a single 4.3-inch Ampire module; uniformity has no published figure in these sources.
| Field | What it means and published values | Ask the supplier for |
|---|---|---|
| Screen size (inch) | 4.3-inch module in one data sheet. [2] | Active area and outline. |
| Brightness (cd/m²) | 400 min, 500 (typ.) at 40 mA in one module. [2] | Luminance and measurement method. |
| Uniformity (%) | Ask: not stated in the reviewed sources; dot pattern grading sets it. [1] | Uniformity and points measured. |
| Colour temperature | White chromaticity x 0.320, y 0.345 (typ.), given for reference only, in one module. [2] | Chromaticity or CCT and tolerance. |
| Input voltage (V DC) | LED string 16.2–19.2 V at 40 mA in one module. [2] | Forward voltage range and binning. |
| Power consumption (W) | About 0.65–0.77 W by editorial calculation from one module's data. [2] | Power at your current. |
| LED lifetime (h) | 40,000 h min, 50,000 h (typ.) to 50% brightness. [2] | Life at your current and temperature. |
| Operating temperature | −30 to 70 °C operating, −30 to 80 °C storage (absolute maximum ratings) in one module; LED current reduced to 30 mA above 60 °C at the panel surface. [2] | Range and derating. |
| Thickness (mm) | 2.9 mm module thickness in one data sheet. [2] | Backlight thickness. |
| Interface | LED anode and cathode pins on the module connector. [2] | Connector or FPC type. |
| Brightness films | Prism films 90–155 µm thick; second sheet crossed at 90°; DBEF on top (3M guide). [3] | Film types, count, orientation. |
08
Paste it into your enquiry below or into an email to a maker, then replace every bracket.
Panel: [model; active area; outline; thickness limit] Optics: [edge or direct; LGP; film stack] Brightness: [cd/m²; uniformity; colour] Drive: [LED current; voltage; constant-current driver; dimming] Life and environment: [hours to 50%; temperatures] Supply: [connector; quantity; samples]
1 company lists this product among what they make. Company figures are quoted from each company's own website; every card states where the relationship came from.
Lists backlight modules for smartphones, tablets and notebooks, and industrial and automotive displays.
Product scope checked 2026-10-12
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A light source at the edge of a light-guide plate, a reflector below, and a diffusion sheet and prism sheets above. [1]
One module data sheet defines it as the time until brightness falls to 50% at 25 °C and 40 mA, rating 40,000 h minimum and 50,000 h (typ.). [2]
LED brightness and life depend on current; the data sheet calls for a constant-current source and lower current above 60 °C. [2]
3M's BEF guide says prisms face the LC module, a second sheet is crossed at 90° to the first, and a DBEF reflective polariser, if used, goes on top closest to the LC module. [3]
In a 2025 Polymers study, raising the cured prism resin's refractive index from 1.564 to 1.574 increased edge-lit backlight luminance by 3.96%. [4]
Sources checked 2026-10-12. The LG Display patent describes one company's backlight construction, the Ampire data sheet one module's backlight ratings, 3M's guide its own brightness films, and a 2025 Polymers paper measured prism-film resin effects on a prototype backlight; values for your display must come from the supplier offered.
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