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Making LCD Screens Readable in Full Sunlight?
irregular_hero asks: "I'm in the process of constructing a navigation and vehicle-management system based on Linux for a car. The trouble I'm having is finding a suitable screen to be mounted in the dash of the car. It seems that traditional SVGA/XGA LCD screens have a really bad tendency to totally wash out in bright sunlight -- in fact, nearly every screen that I've tried turns jet black in sunlight. Are there any SVGA/XGA LCD screens out there that one can get that are sunlight-readable? Or is there a way to make an existing screen not respond so badly to sunlight?"
The Color reflective thin film transistor (TFT) LCD used in the Compaq ipaq handheld, when backlit, is extraordinarily visible, even in full sunlight. Whether it's feasible to determine if there are any larger and similar screens available commerically, I am not sure, but this may be a starting point....
Eschew Obfuscation
Use a 1cm thick sheet of 2mm pitch honeycombed aluminum. Off angle viewing is shit but it makes everything readable by cutting glare and light hitting the screen to zero.
There are a couple of places that sell it but they tend to say "let us give you a quote" instead of just having the product at a given price.
It will be shiny when you get it so get some high quality flat black primer and paint it. It is also very fragile so if you so much as rub your finger across it it's ruined. Sort of like the fins of a radiator.
A cost no object project could use honeycomb aramid fiber (kevlar) or carbon fiber but both of those have drawbacks too. The aramid should only be used in a sealed environment because UV will destroy it in a matter of months. The carbon fiber is just extraordinarily expensive. Neither is as thin as the aluminum so the viewing quality will not be as good either.
If voting were effective, it would be illegal by now.
I dunno where you're mounting it, but you can convert to HUD (Heads Up Display) on the cheap with a mirror. Only problems are 1 - inverting the image, and 2 - need more depth for the display as it is now a prism shape rather than flat (display lies flat or on it's side edge facing w/mirror at 45 deg.)
Alternatively you could get a little open frame CRT from a surplus place like TimeLine (They usually have a wide selection of LCD stuff too if you want to keep experimenting with that).
NEC sells a laptop called the Versa DayLite (aka the LaVie MX in Japan) with a special "reflective LCD" screen that makes it usable outdoors. It also allows it (along with a second internal battery behind the screen) to run up to 8 hours.
On the downside, the screen isn't very good indoors - NEC says it's "suitable for occasional indoor use". The users reviews I've read agree with this. PCWorld also has a review.
Yes, this is exactly the new technology that PDA's are using. When Palm debuted it's m505 using reflective technology, the press whined and complained how the screen was not as bright as the IIIc. What they missed was that the IIIc tried to attack the sunlight problem by using different approach, a high intensity backlight. It was a big power drain, made the device bulky and was still difficult to read in the sun. By using the reflective technology in the m505 the screen became easier to read in the sun and without a bulky backlight. The new techology uses the sun to increase visibility rather than competing in a losing battle to make the backlight brigher than the sun. This makes for thinner devices that are still plenty bright with minimal backlighting at night. Good stuff, I'm waiting for prices to come down though.
We've used 10" and 15" LCDs in kiosks meant for outdoor use. Our supplier added a reflective film that enhances the screens still further. This is apparently possible even on notebook screens.
The downside is that these screens are so bright they can be unreadable at night. Imagine a car headlight shining into your eyes. Also the high intensity causes most colors to wash-out somewhat, especially when looking at the screen from above. Apart from that they are nicely usable indoors.
My blog
Touch Controls, Inc.
800-848-4385 They have what they call the SunTouch ultra high-bright LCD panels (touch screens!)
This may be exactly what you need.
Nothing to see here. Move along.
There are two kinds of LCD: reflective and transmissive. Laptop screens are nearly always transmissive backlit, that is there is a white flourescent light and a grid of red-green-blue filter dots behind it, and electric fields manipulate the liquid crystals to let light pass through in selected sub-pixels. In most office & home conditions this gives much better color, but in competition with the sun, that backlight is bound to lose.
Reflective displays put a mirror behind the LCD. Where a pixel is on, incident light passes through the LCD, is reflected off the mirror, and passes through again. Where a pixel is off, the light is blocked. Most reflective displays are cheap ones in calculators, hand-held games, gas pumps, etc. These are monochrome and with fairly poor contrast all the time. But there are better ones, and it _is_ possible for them to work in direct sunlight, if they are made with enough light blocking capability to stop even sunlight. It also needs a light to work at night -- since this cannot shine through, and it had better not glare in the driver's eyes, it's a little more complicated to add it, but others have cited some off-the-shelf modules you can use. And you will need a contrast adjustment with a very wide range, to handle everything from full sunlight to dim night-time lighting.
To go in a car, it also must handle a wide range of temperatures. Check the freezing and boiling or breakdown points of the liquid crystal material. The LCD displays in gas pumps do handle a pretty wide range, although they need a temperature sensor to adjust the bias in cold weather.