Consider the anti-glare angles for outdoor displays

Using a TFT display outside brings a new set of challenges, not least because the glare created from direct sunlight can make them very difficult to read. Mathew Rehm, Displays Business Manager at Relec Electronics offers a guide for when to choose anti-glare etching or anti-glare coating for an all-angle viewing experience.

The characteristics of TFT displays mean they have become a common feature in our everyday lives. The displays are low in energy consumption and slim, making them convenient and versatile for a wide variety of applications. In the course of a single day, it is usual to come into contact with several as we use our mobile phone, our desktop computer, buy lunch using a supermarket’s automatic checkout and when watching TV at the end of the day. The technology is also popular because it delivers a sharp image with good contrast and clarity of image. However, all of the TFT displays examples mentioned above are indoors.

There are many examples where a slim, high resolution display is required to be in an outdoor setting, for example transport information and ticket kiosks. Large TFT displays are also used for digital advertising signage in town centres where they are exposed to various lighting levels and are viewed from many angles. Anti-glare protection is required in these exterior situations and also for indoor displays where there is a high level of ambient light, for example corporate reception areas or medical settings.

An untreated piece of TFT glass will exhibit many of the properties of a highly polished mirror.  Specular reflection is when incident light from the surrounding landscape is reflected from the glass surface at the same angle it hits the display. The result is that it is extremely difficult to clearly read the image on the display.

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Option 1 – anti-glare etching

There are two common techniques which can be applied to a TFT display so that information is not obscured, even on screens used outside on the brightest of days. These are anti-glare etching or an anti-glare coating. This article looks at the optimum uses for each and where and when they can be applied.

First, let us look at anti-glare etching. This is ideal for use on displays where its optical properties are of a high importance, and where the top surface will be under direct contact, for example when a touch panel is used within the optical stack.

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The treatment involves an etching process using a solvent which incorporates hydrofluoric acid.  This solvent is applied to the cover glass, on either one or both sides, to create an uneven surface which helps to diffuse or scatter the reflected light waves. 

This process means that the display maintains the same hardness level as the original assembly. Another advantage is that the display’s optical properties provide excellent uniformity (gloss value) across the full surface area, thus optimising the backlight performance. Additionally, anti-glare etching provides a higher light transmission level which improves the visual brightness, compared to anti-glare coating. The result produces a strong and durable finish, which is unlikely to need replacing. This is particularly useful if the display’s location is remote or difficult to reach for repair and maintenance.

There are some disadvantages to using anti-glare etching, however. The first is that it is only suitable for some TFT displays. For example, the nature of the process means it can only be applied to a glass display and not to a resistive touch panel display.

Applying anti-glare etching is also a difficult and time consuming process, which is typically reflected in the price of the final product. The increased price may mean it is not practical for some more cost-sensitive applications. 

Option 2 – anti-glare coating

The second option is to choose an anti-glare coating. This treatment can be used for indoor applications as well as those used outdoors and is ideal for displays used under bright light conditions, such as hospitality or medical applications. It is also suitable for an installation which requires the use of a resistive touch panel.

An anti-glare coating creates a similar effect as the anti-glare etching, but this is achieved by spraying the top cover lens with optical micro-particles. These particles cause the incoming light to be scattered and it is the dispersal of light in different directions which reduces the glare.

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This process is easier and less time consuming to apply than anti-glare etching and it can be applied to any surface material because it has no effect on the optical characteristics. It is also suitable for use with resistive touch panels because it does not impact sensitivity. It is also a more cost-effective solution for providing anti-glare protection to displays. This is ideal where the displays themselves are reasonably inexpensive and used in applications that are cost-sensitive.

There are some disadvantages to anti-glare coating which mean that it is not suitable for all use cases. For example, the coating can cause a matte effect on the screen and a poorer gloss uniformity that is achieved with anti-glare etching. For some use cases, in digital signage for example, a high gloss appearance is required to maximise the impact of the advertising content.

The anti-glare coating can also have a slight impact on light transmission which can reduce the visual brightness of the display. In some applications, for example where detailed information is presented on the display, this may detract from the user experience. Another thing to consider is that anti-glare coating is not as durable as anti-glare etching. It may need to be replaced after a period of time as repeated contact or excess force may cause the coating to peel. Replacing the coating poses more of an inconvenience in some locations that others and needs to be weighed up with the overall cost of applying the anti-glare protection.  

Designers and installers have to consider the advantages of each anti-glare process – they are both best-suited for different applications, for the reasons mentioned above.

It is always advisable to discuss the project with a specialist which can listen, advise and recommend the best products for a specific application.

Find out more by visiting https://www.relec.co.uk/display-solutions/screen-enhancements/surface-treatments/ 

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