What makes best Sunlight Readable Display

Why we need sunlight readable display? For the displays that used in outdoor, have you struggled to read the instructions on the display under sunlight? We could see a display that looked good in the outdoor, but the display image wash out in outdoor environment with high ambient sunlight. So for outdoor environment, we need sunlight readable displays, if we use the regular lcd display, it would be looked blurs because the interference of the strong sunlight to the lcd display, so we have to use the sunlight readable displays in the outdoor screen.

1. What is sunlight readable display meaning?

Sunlight readable display means the display that could be read under sunlight, we also call it daylight readable display. the sunlight readable display technologies are including traditional sunlight readable LED display, sunlight readable lcd display, and sunlight readable oled display. The sunlight readable display could be clearly viewed under the strong sunlight without blur or color fade.  A good sunlight readable display would be with high contrast, lower heat emission and power saving.

2. What makes display sunlight readable?

To make the display in sunlight readable or viewable, we have to know the definition of readable or viewable. The visibility means an object is detected by a viewer’s eyes. In scientific words, it means an object’s brightness and contrast is higher than its ambient light, and the different ratio must be higher than human being eyes’ viewing threshold.

So for a display that under the strong sunlight, a display with higher brightness light to complete the ambient light, it would be the key point for making the sunlight readable displays.

There is the way to get sunlight readability:  High brightness compete to the strong sunlight

1) From the test data, the display ambient contrast is declined as the ambient illumination increased, they are inverse relationship

2) The display with lower brightness, the contrast declined faster than higher brightness display

A sunlight readable display = a screen with the brightness on top surface (A) higher than the ambient illumination on screen (B).

that it is A >B for making a sunlight readable display.

A: the brightness on screen top surface

B: the ambient illumination on screen (the ambient illumination means the screen’s reflective light from ambient light)

So we have three directions to create sunlight readable display,

1)     Increasing the brightness on top surface from screen (Coefficient A)

2)     Reduce the reflective light from ambient light on the screen surface. (Coefficient B)

3）  Reuse the ambient light to the screen ( reuse B to A)

A best sunlight readable screen have to improve all these points 1,2,3.

As the research result, for comfortably viewed by eyes, the display brightness needs to 2.5 multiple than its reflective light.

As the result, for making a sunlight readable display, we need a higher brightness light that can compete the ambient light on the screen surface.

There are Three directions for making sunlight readable display:

1.  Increasing display's brightness -- High brightness display

2.  Reuse the ambient light inside the screen -- transflective lcd or reflective lcd

3.  Reducing light reflectance on the surface of screen -- Antiglare surface treatment on the screen.

3. Display solutions for sunlight readable screen:

3.1     High brightness display:

For a sunlight readable led display or sunlight readable OLED screen, since they are active display, we need to increase the light intensive of the LED or OLED screen.

For a sunlight readable lcd display, because lcd is a passive display, the lcd display light would be from LED backlight or ambient light, so we would improve in both direction.

To sunlight readable lcd screen, a common solution is to make high brightness lcd, people make high brightness backlight with more LED chips and use more and better brightness enhance film (DBEF) on high brightness lcd display. However, if for small lcd screens, there would be limited space to place more LED chips, so beside the LED chips, adding DBEF film would improve the brightness in 10%~30%.

The disadvantage of high brightness lcd screen would be in power consumption.

If an outdoor display for handheld, power consumption is a key factor for the small lcd screen and device’s battery.

Another disadvantage of high brightness lcd , especially for large size of outdoor screen, heat dissipation is also important.

3.2   Transflective lcd display and reflective lcd:

Transflecive lcd and reflective lcd could reflect the ambient light on the screen, the reflective light would increase the brightness of lcd screen and reduce the ambient light on the screen.

For transflective lcd display vs. reflective lcd, which is better for sunlight readable display?

Let’s see the test result as following:

2.2 inch transflective tft lcd test in transflective mode (backlight power on, 150cd/m2) and reflective mode (backlight power off)

From the test data, transflective lcd mode have better contrast ratio than reflective mode lcd under 15000 Lux ambient illumination. To the ambient illumination higher than 15000 lux, the contrasts are near for transflective mode and reflective mode, but transflective mode is still better than reflective mode, it might be caused by the lcd screen brightness increased in the transflective mode.

You could find more details about the comparison of transflective tft lcd and high brightness tft lcd : https://www.szmaclight.com/new/How-to-choose-Sunlight-readable-tft.html

4. Surface treatments for the sunlight readable display

The surface treatment could reduce reflectance on the screen surface. the display are made by many materials layers, such as a Sunlight readable tft lcd display with capacitive touch, from the top layer to bottom layer, it is made by top cover lens -->  touch sensors layer-->OCA layer or air gap layer --> top polarizer --> top glass -->  bottom glass-->bottom polarizer-->backlight films.

when the ambient light go through the display, the refraction and reflection happened in each layer. the refraction and reflection light combine to diffuse lights inside the display, it leads to display blur to the screen,  the situation would be worse under the sunlight that with strong incident light to the screen.

The solutions for reducing reflection would be:

4.1  Reduce the reflection of screen surface by AR and AG treatment.

We could add the surface treatments such as Anti-Reflection and Anti-Glare film or apply AR coating. it could reduce 2%~3% surface reflectance on the top surface of sunlight readable display. the surface treatment could be made by additional materials coating on the screen's surface or an external film on the screen.

Anti-glare surface treatment with high haze surface, it could reduce the mirror reflectance on the screen surface.
An external film with AR properties not only reduces reflected light, but also brings some other benefits in some application. a top film always reduces TFT LCD’s surface hardness. And it is susceptible to scratches. On the other hand, AR coating retains LCD’s hardness and touch performance. But it comes with a bigger price gap.

For the sunlight readable tft display with PCAP touch,

An additional linear polarizer on the top of tft screen would also decrease the surface reflectance from ambient light.Or a circular polarizer (O-film) to block reflected light. when ambient light passes through circular polarizer it gets circularly polarized. And when it is reflected, the polarization direction flips by 180 degrees. So when reflected light comes back to the circular polarizer, nothing goes through to viewer’s eyes. But the additional polarizers would make the more thickness to the screen, and reducing the brightness of the lcd screen,  a surface coating with AR or AG treatment are more effective and popular for the sunlight readable lcd display.

The brightness will be reduced if the module requires touch panel or O-Film on it). meanwhile, high brightness displays will generate more heat and use more power than a traditional LCD.

4.2 OCA bonding to replace air gap bonding to the PCAP touch screen

OCA bonding would help to reduce the reflection light of the lcd display. Air-gap reflection is the main culprit causing worse sunlight readability. We can improve it from two directions. Add AR films or AR surface treatment on both interfaces of internal air gap. it could reduce the reflection ratio from 8.5% to 2%.

·        The most effective way is to eliminate air gap totally, by using OCA bonding (optical bonding). OCA bonding means we fill air gap with special optical adhesive (OCA), to smooth out the area’s refraction index differences. it leads to the reflectance by internal air gap drops from 8.5% to 0.5%. Optical bonding is expensive but effective way to improve TFT LCD sunlight readability. Moreover, no air gap means no moisture condensation and fogging for the sunlight readable tft display.

5. Typical types of sunlight readable displays:

5.1  Sunlight readable oled display or led display.

Traditional LED display can be in higher brightness when in outdoor working, but common LED screen is hard to make with high resolution(PPI). so it is hard to get a high quality display effect. To the OLED display, even the organic led display(OLED) can be in high resolution, but its cost is more expensive than lcd display. in the same time, LCD's lifetime is longer than oled display.

5.2  monochrome lcd display

Monochrome lcd display can be used for sunlight readable screen, Its display modes have TN or stn lcd with Positive mode, they are with dark display letters on lighter background. the sunlihgt readable lcd can be reflective or transreflective display mode, the costs are similar for monochrome reflective lcd, transflective lcd, and transmissive lcd, Transflective or reflective monochrome lcd are the common and economy solution for sunlight readable lcd displays. Since the reflective lcd and transflective lcd has the lowest power consumption than other sunlight readable display,  reflective lcd doesn't need backlight, while transflective lcd only need the backlight in dark environment. the monochrome lcd is easily to custom make, its tooling cost is also cheaper than other custom tft display or oled display.

5.3 Sunlight readable tft display:

For lcd displays in daylight and outdoor application, if you'd like color displays, we would suggest sunlight readable tft displays, because the cost of sunlight readable tft is lower than color OLED display,  the color tft displays have longer lifetime than OLED display. Different to traditional monochrome lcd, tft lcd screen have full display colors, the high brightness TFT and transflective tft lcd display would be good solutions for sunlight readable outdoor display.

6.  Sunlight readable display from Maclight:

Maclight's high brightness TFT LCD panels are featured with brightness up to 1000 nits. high brightness tft by choosing a very bright backlight to keep the display visible even when the sun is on it. we could upgrade the backlight to dramatically increase brightness with our high-quality LED backlights.

Maclight's sunlight readable display models are available in resistive touch panel and capacitive touch screen, but the brightness would be affected after adding the touch panel.  Maclight Sunlight Readable LCD Modules (High Brightness TFT Display and transflecitve tft lcd display module) are suitable for outdoor applications. Maclight transflective tft including 1.8 " , 2.2" transflective tft, 2.4" tranflective tft display, 2.8", 3.0, 3.5" transflective. Maclight's  high backlighting sunlight viewable TFT display sizes including 2.4 “ tft , 2.8” tft lcd, 3.5"tft LCD, 4.3”, 5",7" and 10.1 inch tft lcd, the sunlight readable display sizes are up to 85" , the upgraded backlight brightness can be up to 3000 nits in maximum.

Please find some sunlight readable displays as following:

1.8" high brightness tft display module:

1.8" sunlight readable tft lcd

128(RGB)x160 pixels

1000 cd/m2 hight brightness

8 bits/16 bits MCU interface

256k full color tft lcd

2.4" transflective tft lcd: