Transreflective LCD monitors for sunlight

Whether it's 6,4” (8,4”, 10,4”,...17”) or 19'' LCD monitors that are meant to be used in bright sunlight or other areas with poor lighting conditions, you need special precautions in order to prevent overheating. For a lot of interfaces, we will go as far as to say that strong fluorescent tube lights are not recommended at all. This is due to them requiring twice the ammount of power to achieve 1000 ca/m2. Because of this, panel-PC solutions based on traditional monitor technology with tramsissive panels and special fluorescent tube lights should be avoided.
Irontech has therefore chosen to standardise transreflective technology in the cases where readability in difficult lighting conditions is a must. This goes for just monitors or for panel-PC solutions.

Self adjusting light

To add readability in i.e. sunlight, without the need for more electrical energy, we saw the introduction of transreflective screens. These screens reflect most of the sunlight the monitor is exposed to, and automatically increase or decrease the light emanating from the screen depending on how much light that shines on it. Transreflective screens therefore reduce the need for manual light adjustment.
Below are two simple images which illustrate how this technology works.
 

Transreflective technology with backlight                      Standard technology with backlight

When only parts of the screen is exposed to sunlight

Most people have had the experience where they're sitting at work on a day with the sun shining outside, and we think that's great, until the sun starts shining on your computer screen, making you have to pull the curtains to cover your screen up so you can see what's on it. For industrial users, it's not that simple. There the screen is often attached to a wall or a rack, making it immovable. In these situations, it's nice to have a monitor that is readble in sunlight, all you would have to do is turn up the light. But what happens when the sun suddenly gets covered by a cloud? Then you would have to adjust the light settings again, turning the light down. In work situations where this has a tendency to occur frequently, tuning the light manually all the time is very impractial. These adjustments would need to happen automatically.
The advantage of special fluorescent lights is that they can provide great background lighting, from 1600 cd/m2 and more. The solutions Irontech can offer, however, will give an effect of up to 1200 cd/m2. A ''normal'' LCD will only give about 250 cd/m2.
In most situations the entire screen will not be affected by sunlight, only parts of it. Maybe only 10%, 20% or 50% will be. For LCD monitors with powerful lighting, the solution has to be to increase and reduce the brightness on the whole screen. For users with transreflective monitors, only the area exposed to the sun will be adjusted, and it will happen automatically. This way, the difference between normal and intense sunlight will be greatly reduced. We have tried to simulate this effect on the images below.
 

Standard LCD                   High bright LCD                  Transreflective LCD

We now know that regular LCDs are usually not suitable in situations with poor lighting. We also know that even if useable, a lot of manual adjustments would have to be used all the time to get the brightness the way we want it. And last but not least, we know that monitors with special fluorescent tube lights are not able to only adjust the brighness on some parts of the screen.

 What about heat?

As with all other electronic products, heat can be a major issue, and this problem usually occurs in enclosures, the type industries use. Enclosures can be based on the need for minimal electromagnetic or RF radiation in or out of the monitor. However, it can also be based on so called IP requirements on imperviousness to particles like dust or water. Others may have requirements relating to the Ex standards for explosion hazardous areas or related to the Atex standards. Regardless, enclosures create a potential heat problem. For most PC solutions, parts of this problem can be solved with fans.

Based on numbers from distributors of sun cell panels the sun gives an added effect of about 1000 watt per m2. Based on 19'' screens, this will produce 250 watt radiation. This is 60-70 watt more than the technology Irontech uses. In addition to this, monitors based on traditional technology and that are meant to be used in sunlight, are given extra effect to produce the brightness that is intended. A part of this naturally turns into light, but we don't see it as unreasonable that added heat is somewhere between 20-30 watt. An LCD screen that is designed to be readable in sunlight based on traditionall lightning will therefore absorb 80-100 watt more than LCDs from Irontech. You need exceptional cooling to handle this.

This problem naturally does not get any less severe if the monitor and the enclosure are exposed to sunlight. Many industrial screens also have a protective ''glass plate'' (plastic) in the front, which absorbs the heat compared to regular office monitors.

Transreflective monitors have the advantage that they reflect a great ammount of the heat (and light) rather than to store it in the enclosure.
 

Conclusion

 There are actually very few disadvantages this technology compared to the solutions that use high intensity fluorescent tubes for readability in sunlight. A short summary follows:

• The brightness on transreflective LCDs does not require regular adjustments as they adsjust themselves.
• Transreflective screens are easier on the eyes when only parts of the screen is exposed to bad lighting.
• There will be less heat issues due to the monitors reflecting a lot of the energy in sunlight. These monitors are therefore more suited for enclosures.
• Monitors with transreflective technology (1200 cd/m2) give off a little less light than monitors with special fluorescent tubes (1600-1800 cd/m2). Typical standard values for regular LCDs is 250 cd/m2. In return, transreflective LCDs do not have size limitations, and can be delivered in multiple sizes like 6,4”, 8,4”, 10,4”, 12,1”, 15”, 17”, 19” and so on.

Irontech's goal is to be among the best providors of professional computer equipment in Norway. To manage this, we have to be able to provide some of the best products we can find, but still compete with other companies when it comes to price.