EL backlight brightness for Transflective vs Transmissive displays

EL backlight brightness vs LED

The LED backlight or EL backlight brightness on Character LCD modules, Graphic LCD modules and Segment LCD modules have different levels of brightness depending on the type of polarizer that is installed. For additional information on LCD display polarizers: click here.

Although electroluminescence backlights have decreased in popularity in the last few years, we still come across them when building replacement LCDs for one of our customers. One question customers ask about is how to make the EL backlight as bright as an LED (light-emitting diode) backlight?

Brief history of LCDs with an EL backlight

In the past, customers have chosen electroluminescence backlights because they are thin and provide a more even light flow than older LED technology; but this has changed thanks to advances in LED and diffuser technologies. LEDs have become the industry standard for LCD backlight for several reasons:

  • They have a half-life of 50K to 70K hours, versus EL backlights with a half-life of 3K hours.
  • New diffuser technology allows the LED backlights to have a more even light flow and eliminates hot spots.
  • LEDs do not produce any noise or electrical interference that is associated with EL backlights.
  • They can be built with SMT (Surface Mount Technology) components allowing them to be as thin as EL backlights.

Increasing the EL backlight brightness

It is much easier to increase the brightness of a LED backlight than an electroluminescence backlight. Since LEDs are DC (Direct Current) it is a matter of modifying a resistor value to increase current flow to increase backlight brightness.

It is possible to increase the brightness of an EL backlight with complex circuitry, but the easiest method is to swap the top polarizer of the LCD glass from Transflective to a Transmissive.

How Polarizers affect backlight brightness

When ordering a LCD display with either a LED backlight or an EL backlight you have the option of two polarizers: Transflective and Transmissive. There is no difference in cost or lead time between Transflective and Transmissive polarizers.

The advantage of the transmissive polarizer on a monochrome LCD display equipped with an LED (light emitting diode) or electroluminescent is that the backlight brightness will be brighter. The disadvantage of the transmissive polarizer is that you can only read the LCD module when the backlight is turned “ON”.

The advantage of the Transflective polarizer on a LCD display module is that you will be able to read the LCD module with the backlight “OFF”, but the backlight brightness will not be as bright.

The photos below are of a custom LCD module with these characteristics: TN, positive mode with a white LED backlight.

The display on the left is Transmissive. The display on the right is Transflective.

Transmissive Transflective

Replacing EL backlights with LED

EL backlights have a high MOQ (Minimum Order Quantity). One solution is to replace the El backlight with a low profile LED. This is not a direct replacement, but with some redesign, it is possible.

Need help with your LCD design? Contact Focus LCDs today at 480-503-4295.