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Comparing Transflective and Sunlight Readable Displays

Application Note FAN4210

This application note will discuss the available options in enhancing display visibility in bright environments. 

 

1. Introduction

This application note will discuss the available options in enhancing display visibility in bright environments. Displays can be difficult to view under bright ambient conditions such as in outdoor applications. This note will compare the differences of transflective displays and sunlight readable transmissive displays. These are two popular options of compensating for the decreased visibility caused by the ambient environment. This application note will provide an example of each display and discuss the advantages of each. The three displays used in this analysis range from a sunlight readable transmissive TFT, a transflective TFT and a transflective graphic LCD. The displays are provided below.

fan4210-1.png fan4210-2.png fan4210-3.png

E35KA-FW1000-N

E20RB-FW345-N

G126FLGFGSW64T33XAR

In order from left to right the displays are as follows: sunlight readable, transflective TFT and transflective graphic LCD.  Below is a brief description of each display. The descriptive characteristics vary between the graphic and TFT display types. The backlight voltage is included to note the difference in power consumption between the sunlight readable and transflective TFT’s.

 

Display Description  Size    Polarizer     Resolution  

 Backlight Voltage 

E35KA-FW1000-N Sunlight Readable TFT 3.5" Transmissive 320 x 480 Pixels 15.0 V
E20RB-FW345-N Transflective TFT 2.0" Transflective 240 x 320 Pixels 3.3 V
   G126FLGFGSW64T33XAR   

   Transflective Graphic LCD   

   80 x 57 mm   

   Transflective   128 x 64 Dots 3.0 V


2. Method Descriptions

The first method is to use a transflective display. Transflective displays reflect the available light off the surface to illuminate the image. These displays are called transflective because they reflect and transmit the light; transflective = reflective + transmissive. Focus LCD’s offers both graphic and TFT transflective display options. Both display types are great for outdoor applications where bright ambient lighting is available. A benefit of transflective displays is reduced backlight power. The backlight can be turned off when utilizing the reflective aspect of the display. This feature makes transflective displays favorable to battery powered applications.

fan4210-4.png fan4210-5.png

The second method is to use a transmissive TFTs with a high-powered backlight to compensate for bright ambient lighting. These TFTs are very bright and can range from 800-1100+ nits to illuminate the display. A non-sunlight readable transmissive TFT would have a much lower brightness and would look washed out or have limited visibility in a bright environment. Sunlight readable TFTs can maintain a detailed and colorful image in a variety of environments which make them a great solution for indoor and outdoor applications. The backlight is illuminated to a high brightness to make the image visible even in direct sunlight.

3. Example Lighting Environments

   B/L    Ambient Condition 

Examples 

(Transflective TFT, Sunlight Readable TFT, Transflective Graphic) 

ON Bright Indoor Lighting fan4210-6.jpg
OFF fan4210-7.jpg
ON  Dark Environment  fan4210-8.jpg
ON Full Sunlight fan4210-9.jpg
OFF fan4210-10.jpg


4. Power Consumption

A notable factor when choosing between sunlight readable transmissive and transflective displays is the power consumption of the backlight. The backlight consists of a number of LED’s in series and/or parallel. The sunlight readable TFT’s will have more LED’s to provide a higher brightness. It is important to consider the backlight circuit when choosing an LCD because they are often the biggest power drain of a display. Below are the backlight LED circuits for the displays in this example.

fan4210-11.png fan4210-12.png fan4210-13.png

Sunlight readable transmissive TFT’s and tranflective displays are on opposite ends of the spectrum of power demand. The backlight of a sunlight readable TFT requires high voltage and current to overpower the bright ambient environment. This power becomes more significant with the size and brightness of the display. A transflective display uses the bright ambient lighting to illuminate the screen, thus removing the need for a backlight when these conditions are available. A comparison of power demand on the backlight between these display types are seen below.

Display Size 

 Brightness (Nits) 

 # of LEDs  Voltage (V)  Current (mAh)  Power (mWh)  Power (kJ) 
Sunlight Readable Transmissive TFTs
E35KA-FW1000-N
3.5" 1000 10 15 60 900 3.24
E40RC-FS1000-C 4.0" 1000 12 18.6 40 744 2.68
    E43RG64827LW2M1000-R    4.3" 800 18 28.8 40 1152 4.15
Transflective TFTs
E20RB-FW345-N 2.0" 345 4 3.0 80 240 0.95
E22RB-FW1180-N 2.2" 1180 6 19.5 20 390 1.4
E35RC-FW115-N 3.5" 115 6 18.6 20 372 1.34
Transflective Graphic LCDs
G126FLGFGSW64T33XAR 128x64 -- 6 3.3 50 165 0.594
G126GLGFYSY6WT 128x64 -- 8 4.7 80 376 1.35
 G160BLGFGSW6WTC3XAM   160x100   -- 3 3.3 60 198

0.712


4. Considerations

The reflective and transmissive properties are inherent to each display. These modes specify the type of polarizer within the display and are not something that can be turned on or off. The transflective display will reflect the light in bright ambient conditions. In dark environments the transflective display can use the backlight to illuminate the display. The backlight does not make a significant difference for a transflective display in direct sunlight. Power can be conserved when the backlight is not used. This makes transflective displays energy efficient and favorable for battery powered applications. A standard transmissive TFT (non-sunlight readable) would have limited visibility and a washed-out appearance in direct sunlight.

Sunlight readable TFTs maintain color vibrancy and contrast in bright ambient lighting. The high brightness of the sunlight readable TFTs increases the power demand on the backlight, this can result in an increase of heat emission from the display. Heat emission and power consumption should be considered for outdoor applications specifically in high temperature environments. When not in a bright environment the display’s backlight can be a lowered to avoid eyestrain and decrease power demand.

5. Summary

Focus LCDs offers a variety of display options for bright ambient environments and outdoor applications. Sunlight readable TFTs are a great solution for maintaining a vivid and colorful image in any lighting environment. Transflective displays, both TFTs and graphic LCDs, can illuminate the display with or without the backlight. These displays have the benefit of low power consumption because the backlight can be turned off utilizing the reflective polarizer of the display. This makes transflective displays favorable for battery powered devices. It is important to consider these factors when choosing your next display and Focus LCDs has a solution for any application. For more information visit FocusLCDs.com.

DISCLAIMER

Buyers and others who are developing systems that incorporate FocusLCDs products (collectively, “Designers”) understand and agree that Designers remain responsible for using their independent analysis, evaluation and judgment in designing their applications and that Designers have full and exclusive responsibility to assure the safety of Designers' applications and compliance of their applications (and of all FocusLCDs products used in or for Designers’ applications) with all applicable regulations, laws and other applicable requirements.

Designer represents that, with respect to their applications, Designer has all the necessary expertise to create and implement safeguards that:

(1)     anticipate dangerous consequences of failures

(2)     monitor failures and their consequences, and

(3)     lessen the likelihood of failures that might cause harm and take appropriate actions.

Designer agrees that prior to using or distributing any applications that include FocusLCDs products, Designer will thoroughly test such applications and the functionality of such FocusLCDs products as used in such applications.