Understanding Sunlight Readable Displays

Understanding Sunlight Readable Displays
March 8, 2017 Eric Hawkins
In Journals

Not all displays perform well in bright lights. For example, displays used in cell phones, tablets and laptops have poor performance in sunlight but are readable inside where the brightness is much lower.

Sunlight readable means that the display is not ‘washed-out’ from sunlight or high brightness environments.

Examples of products that require Sunlight Readable Displays:

      1. Test Equipment
      2. Automotive/Marine
      3. Communications
      4. Solar/Battery powered products
      5. Medical

Which types of displays are best for sunlight?

Two methods used to make displays readable in direct sunlight are:

      1. Choosing the optimum polarizer
      2. Increasing the backlights brightness

1. Choosing the optimum polarizer

There are 3 types of polarizers available when building a LCD

      • Reflective – Best choice for sunlight readability
      • Transflective – Second best choice for sunlight readability
      • Transmissive – Third choice. The backlight must be ON for the display to be readable

Reflective Polarizer

Displays that work best in sunlight contain a reflective polarizer.

reflective.jpg

The reflective LCD polarizer is nothing more than a mirror applied to the bottom layer of glass. It reflects 100% of the sunlight entering through the top layer of glass back towards the user. The brighter the sunlight, the easier to read the display.

Transmissive Polarizer

transmissive.jpg

A Transmissive LCD polarizer, unlike the reflective polarizer, does not reflect any sunlight. All light must be provided by the backlight. 100% of the backlight passes thought the bottom and top layer of glass towards the user. The backlight must be ON for the display to be readable. Ambient light from office lights or sun light will pass through the bottom layer of glass and not reflect back towards the top glass; so sunlight will add very little illumination to the display. The brighter the sun, the more washed-out the display.

Transflective Polarizer

transflective.jpg

The Transflective LCD polarizer is a combination, or hybrid, of the Reflective and Transmissive polarizers. It reflects some of the ambient (sun) light passing through the front of the glass and at the same time allows some of the light from the backlight to pass through to the front layer of glass. It is good in direct sunlight, but will not produce as sharp of contrast as a Reflective polarizer.

2. Increasing the backlights brightness

A select number of LCD technologies must use a Transmissive polarizer. It is possible to make a Transmissive display more readable in sunlight by increasing the brightness of the backlight. The brightness is increased by adding more LED (light emitting diodes), the additional LEDs will draw more power and in some cases require a one-time tooling fee.

As a general rule, a Transmissive display will need a brightness of 800 NITs or brighter. A NIT is how much light one candle will produce.

Questions to ask your customer:

    • Do you need this to be sunlight readable?
    • Does this need to be readable in the dark?
    • Is this a battery or solar-powered product?

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