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Q&A with Chris Bartram, Crystal Display Systems (CDS) Managing Director, who discusses transparent display technology


Q: Tell us more about transparent displays

A: Interestingly, despite their name, transparent displays don’t go clear when they are powered off;they are dark – somewhat transparent. For them to become transparent, they need a voltage across the display, and when you apply a white pixel, the displays become transparent at a rate of around 15%.

These type displays can be used in sunlight since they have films with sunlight-readable properties. However, you will also need to ensure there’s sufficient light behind the transparent display, as well as ensure limited dissipation so the backlight is more effective in sunlight conditions. When used in direct sunlight you should also apply UV protection on the front glass.

Transparent displays don’t include backlights and so the user/integrator must supply their own backlighting for the box/showcase solution with a sufficient brightness to ensure a good crisp image to optimise the performance. The backlight should be white for optimal contrast and image quality.

These displays work with a full range of touchscreen technologies, but if you can use it, we recommend infra-red which gives excellent image quality and finish with its pure glass front (i.e. no transparency lost through wires or ITO layers like with other technologies).

The transparent displays’ standard operating temperature is 0-50oC, but for extended temperature versions talk to your manufacturer/supplier.

Q: Do transparent displays suffer from heat problems?

A: Heat is normally not a problem since the displays produce very little heat themselves; they have no backlight just a simple connector box on the back incorporating a small PCB. They will only be affected by heat from the LED backlighting within a showcase box solution, but as every application/design is different, it’s difficult to comment on how much heat. Air vents can be used for heat dissipation and ventilation, if this is a concern.

We recommend LED backlighting to help keep heat to a minimum. The standard LEDs we use are 6000K cool/daylight white. They are fixed on and non-dimmable.

Q: Why are the backs of some transparent displays mirrored?

A: This is standard on all displays now, since the mirror acts as a contrast enhancement film and increases the contrast and colour depth of the image and maximises the light within the showcase.

Q: What brightness is needed behind the screen?

A: This depends on what brightness you want at the front of the screen, but, with transparency of around 15-20%, to achieve 300cd you will need around 1500cd. With high-brightness white LEDs this is not a problem and not expensive.

Our experience with incorporating transparent displays in shop windows has made us consider conditions such as:

1. Window position;

2. Level of direct sunlight;

3. Any potential reflections on the outside of the store widow;

4. Light needed behind the transparent screen;

5. Best location for the display, say, inside the store as people enter the main doors; and so on.

Q: How does content work on a transparent display?

A: Content is simply created in the same way for any other display, but you must remember that black stops the light completely and white makes the display translucent (see-through).

There is an interface kit that can be used for uploading content, either via a USB (for simple local updates) or VGA or HDMI inputs to connect a PC or media player of choice.

Several options help with the content, the most common being MPEG4 at a resolution of 1920 x 1080. With an interface card, all file formats/codecs can be accepted.

Content can be updated remotely by connecting your PC or media player via the HDMI input on the interface card provided.

Q: How do colours work on transparent displays?

A: Basically, if you take the two extremes of black and white, black blocks out the light so nothing can be seen behind the screen, whereas white becomes translucent so it is ‘see-through’, and

all those colours in between become more or less transparent depending on how dark or light

they are. For example, dark blue and grey are not very translucent but light pink and pale blue are very translucent.

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