01
More Compact Backlight Structure
A shorter optical distance reduces the space required between the LED light-source area and the optical layers, helping reduce the depth of the backlight module.
BACKLIGHT TECHNOLOGY
What Is Optical Distance in an LCD Backlight? Understanding OD10 and OD20 for High-Brightness Displays
When sourcing a high-brightness LCD display, buyers usually compare brightness, panel specifications, operating temperature, power consumption and cooling design. But another important part of the display is often overlooked: the LED backlight.
One parameter commonly used in direct-lit LED backlight design is OD, or Optical Distance. Terms such as OD10, OD15, OD20, OD25 or OD30 describe the optical distance inside the backlight structure rather than a brightness level or quality grade.
QUICK ANSWER
OD10 generally means an optical distance of approximately 10 mm, while OD20 means approximately 20 mm. A smaller OD can help create a more compact backlight, but it also gives LED light less space to spread and mix. For this reason, low-OD backlights require more careful control of LED pitch, lenses, diffusion and uniformity.
01
What Does OD Mean in an LCD Backlight?
OD stands for Optical Distance.
In a direct-lit LED backlight, LEDs are distributed behind the LCD panel. Above these LEDs are optical components such as a reflector, diffuser and optical films that help spread and manage the light before it passes through the LCD.
The distance available for the LED light to spread and mix before reaching the diffuser is commonly referred to as the optical distance.
OD10
≈ 10 mm
Short optical mixing distance
OD20
≈ 20 mm
Longer optical mixing distance
Other OD values also exist. Depending on the display size, backlight manufacturer and optical design, OD15, OD25, OD28, OD30 and other configurations may be used.
Important:
OD is not a standardized quality grade. A smaller OD does not
automatically mean a better or brighter LCD display.
02
Why Does Optical Distance Matter?
Imagine placing several small light sources behind a translucent white panel.
When the light sources are farther away from the panel, their beams have more distance to spread and overlap. Move those same light sources closer to the panel and individual bright spots become easier to see.
A direct-lit LCD backlight faces a similar challenge.
LARGER OD
More Light-Mixing Space
LEDs have more distance to spread before the light reaches the diffuser, making uniform illumination relatively easier to achieve.
SMALLER OD
More Compact Structure
The backlight can be thinner, but LED distribution, lenses and diffusion must be engineered more carefully to control visible hotspots.
This means reducing optical distance is not simply a mechanical change.
The LED layout, LED pitch, secondary lens, reflector, diffuser and other optical materials all have to work together.
The goal is not simply to achieve the smallest possible OD. The goal is to achieve the required brightness and uniformity within that optical distance.
03
OD10 vs OD20: What Is the Difference?
OD10 and OD20 are two configurations frequently used in commercial direct-lit LCD backlights, including many high-brightness designs.
| Factor | OD10 | OD20 |
|---|---|---|
| Optical Distance | Approx. 10 mm | Approx. 20 mm |
| Light-Mixing Space | Shorter | Longer |
| Backlight Depth Potential | Lower | Higher |
| Optical Design Requirement | More demanding | More forgiving |
| Hotspot Control | More challenging | Relatively easier |
| Slim Design Potential | Higher | Moderate |
| High-Brightness Capability | Depends on complete design | Depends on complete design |
| Cost | Depends strongly on LED density and optical design | Depends on complete backlight design |
The most important point is that OD10 is not automatically brighter than OD20.
Brightness is determined by the complete backlight system, including LED specification, quantity, optical efficiency, LCD transmission, power design and thermal conditions.
04
Why Is OD10 More Demanding to Design?
With only around 10 mm of optical distance, LED light has less room to spread before reaching the diffuser.
If the LED spacing is too large, or if the optical lens and diffuser are not properly matched, individual LED positions may become visible.
01
Visible Hotspots
02
Dark Areas
03
LED Patterns
04
Uneven Brightness
This is why LED pitch becomes especially important in a compact direct-lit backlight.
A lower OD may require a denser LED arrangement, different secondary lenses, different diffusion characteristics or a combination of these measures.
A properly designed OD10 backlight is not simply an OD20
backlight with 10 mm removed from the housing.
It must be engineered as a complete OD10 optical system.
05
What Is a Dense Direct-Lit LED Backlight?
In many high-brightness displays, VMision uses a dense direct-lit LED backlight structure.
In the Chinese display supply chain, this arrangement is sometimes informally called a “starry-sky backlight” because, before the diffuser and LCD panel are installed, hundreds of LED light sources can be seen distributed across the entire backlight area.
For international customers, we normally describe this more technically as a Dense Direct-Lit LED Array.
INSIDE THE BACKLIGHT
Dense direct-lit OD10 LED backlight used in a VMision
high-brightness LCD display.
Hundreds of LEDs are distributed across the backlight area in a
regular matrix, providing the foundation for high light output
and uniform illumination.
The dense distribution allows the backlight to generate and spread a large amount of light directly behind the LCD panel.
But LED quantity alone does not determine performance.
LED Specification
+
LED Quantity
+
LED Pitch
+
Optical Lens
+
Diffuser & Films
+
Power Design
Together, these determine the actual brightness and uniformity of the finished backlight.
06
Why VMision Uses OD10 in Many High-Brightness Displays
VMision uses dense direct-lit OD10 backlights in many of our high-brightness and outdoor LCD products.
We select OD10 based on the complete backlight design rather than the optical distance alone.
For many high-brightness products, a dense direct-lit OD10 structure allows us to achieve high light output while keeping the backlight relatively compact.
02
Suitable for Dense High-Brightness LED Arrays
Combined with an appropriately designed dense LED layout, OD10 can support the high light output required by commercial high-brightness LCD applications while maintaining controlled brightness distribution.
03
Better Use of Internal Space
High-brightness and outdoor displays also require power supplies, controller boards, cooling components, air channels, filters and structural parts. A compact backlight leaves more flexibility for the complete mechanical design.
04
Balance Between Brightness and Thickness
OD10 gives engineers another way to control product depth while still allowing a direct-lit high-brightness architecture to be used.
07
Does OD10 Improve Heat Dissipation?
Not by itself.
This is an important distinction because OD describes an optical distance, not the cooling capability of the display.
A dense high-brightness LED backlight can generate considerable heat regardless of whether it uses OD10 or OD20.
LED Efficiency
Total LED Power
PCB Design
Metal Backplate
Heat Conduction
Airflow
Cooling Fans
Enclosure Design
For outdoor LCD displays, ambient temperature and solar radiation must also be considered.
OD10 is an optical and structural choice.
Thermal management must still be designed according to the actual
LED power, enclosure and operating environment.
08
Why Do We Still Use OD20?
Because OD10 is not the correct solution for every product.
VMision also uses OD20 backlights in selected high-brightness displays where it better matches the required product structure.
Compared with OD10, the additional optical distance gives LED light more space to spread and overlap before reaching the diffuser. This can make brightness uniformity easier to control.
Brightness
Uniformity
Thickness
Complexity
Cost
For certain screen sizes, brightness targets and mechanical structures, OD20 can provide a very practical balance between all five factors.
If OD20 already achieves the required brightness, uniformity, thermal performance and product structure, there is no engineering reason to force the design to OD10 simply to obtain a smaller number.
09
Does OD10 Cost More?
Sometimes, but OD itself does not determine the price.
A simple OD10 backlight is not automatically more expensive than a sophisticated OD20 design.
The actual cost comes from what is required to achieve the target brightness, uniformity, thickness and reliability.
LED Quantity
Number of LEDs used across the backlight area
LED Specification
Efficiency, output and operating characteristics
LED Pitch
Spacing between individual light sources
Optical Components
Lenses, reflector, diffuser and optical films
PCB & Backplate
Electrical and structural design of the backlight
Thermal System
Heat conduction, airflow and cooling components
When a smaller optical distance requires a denser LED arrangement or more demanding optical components, the total backlight cost may increase.
Reducing optical distance does not automatically reduce cost.
In many high-performance OD10 designs, the cost comes from the dense LED array and the optical, electrical and thermal engineering required around it.
10
The Same Brightness Does Not Mean the Same Backlight
Consider two commercial LCD displays that are both specified at 3,500 nits.
The headline brightness value may be identical, but their internal backlight structures can be very different.
How many LEDs are used?
How are the LEDs distributed?
How uniform is the brightness?
How much power does the backlight consume?
How is the generated heat managed?
How does the system behave during continuous operation?
This is why backlight cost should not be compared as an isolated component.
The cheapest backlight is not automatically the most economical solution for a commercial display expected to operate for several years.
At the same time, using a more complex and expensive OD10 structure where it provides no practical benefit is also unnecessary.
11
What Should Buyers Compare Besides OD?
Knowing whether a display uses OD10 or OD20 can help you understand its internal design, but OD should never be the only purchasing criterion.
What brightness does the finished LCD actually achieve?
Is illumination consistent across the complete display area?
How is the direct-lit LED array distributed behind the LCD?
How much electrical power is required at maximum brightness?
How is heat transferred and removed from the backlight?
Can the complete display operate reliably at the required temperature and installation location?
12
OD10 or OD20: Which Is Better for High-Brightness LCD?
Neither can be described as universally better.
When the goal is a compact high-brightness backlight and the LED density, optical structure and thermal system are correctly engineered, OD10 can provide important design advantages.
This is why VMision uses dense direct-lit OD10 backlights in many of our high-brightness and outdoor LCD displays.
For other designs, OD20 can provide an excellent balance between optical performance, module depth, manufacturing complexity and cost.
A BETTER WAY TO COMPARE OD10 AND OD20
The right choice depends on the complete display design —
including brightness, uniformity, product thickness,
thermal performance and cost.
FAQ
Frequently Asked Questions
What does OD10 mean in an LCD backlight?
OD10 generally refers to an optical distance of approximately
10 mm between the LED light-source area and the diffuser or
optical section of a direct-lit LED backlight.
Is OD10 brighter than OD20?
No. OD describes optical distance rather than brightness.
Brightness depends on the LED system, optical efficiency,
LCD transmission, power design and complete backlight structure.
Why is OD10 used in high-brightness LCD displays?
A properly designed OD10 structure allows the backlight to remain
relatively compact. When combined with a dense direct-lit LED
array and matched optical components, it can be well suited to
high-brightness commercial displays.
Why does VMision use dense OD10 backlights?
Many VMision high-brightness and outdoor LCD products use dense
direct-lit OD10 backlights because the architecture fits our
requirements for high light output, uniformity and compact
mechanical design. Selected products use OD20 where it provides
a better overall balance.
Is OD10 more expensive?
Not automatically. OD itself does not determine cost. However,
achieving high brightness and good uniformity within a short
optical distance may require a denser LED arrangement and more
carefully matched optical components, which can increase the
cost of the complete backlight.
Are there OD values other than OD10 and OD20?
Yes. OD is not a fixed grading system. Depending on the backlight
design, values such as OD15, OD25, OD28, OD30 and others may also
be used.
CONCLUSION
Optical Distance Is Only One Part of a High-Brightness Backlight
OD10 provides a shorter optical distance and greater potential for a compact backlight, but achieving good uniformity within that space requires a properly matched LED array and optical system.
OD20 provides more light-mixing distance and can offer an excellent balance when a slightly deeper backlight is acceptable.
VMision therefore does not select a backlight simply by choosing the smallest OD available.
We use dense direct-lit OD10 backlights in many of our high-brightness and outdoor LCD displays, while OD20 is used in selected designs where it better fits the complete product.
Brightness
Uniformity
Thickness
Power
Thermal Performance
Reliability
Cost
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