Reader Q&A

Using a Computer Screen as a Mirror

I found your email address on a website about pencomputing and displays. I have been wondering for some time if it's possible to write software to make a "mirror" or reflective surface on a computer display. Do you know if it's possible? Has it been done? I would love to know more about this, as I think a widget [Ed: a small, specialized desktop application] would be very popular with those of us who work all day at a computer and hate to miss that piece of spinach in our teeth from lunch.
-- Christine Hollender

Technology Editor Geoff Walker answers:

Christine, the reflectivity of an LCD display's surface is a physical characteristic that isn't changeable through software. Many LCD displays include an anti-reflective (AR) coating intended to reduce the amount of light reflected from the display. In general, the more light that's reflected from the surface of a display, the lower contrast the image on the display appears. If you take a notebook screen outdoors into the sunshine, so much light is reflected from the screen that you can't see the image on the screen at all.

However, if you set all the pixels on the screen to black (or just turn off the screen) and take it into a brightly lighted area, even with AR there is still enough light reflected from the screen to allow seeing at least some of your own reflection. How clearly you can see your reflection depends on whether the LCD surface also has an anti-glare (AG) treatment. AG scatters any light reflected from the screen, making the reflection very fuzzy. Many of the very latest widescreen laptops don't have AG (they have "glossy" or "glare" screens), so the reflection from their screens is much clearer.

There is one exception to the above description, and that's reflective displays. These displays work by reflecting ambient light off a mirror layer behind the pixels. You can see yourself more clearly in these screens when the screen is off because they are designed to reflect more light. Transflective displays use a partial mirror behind the pixels, so the same effect happens with them, just not as strongly. Blackberry PDAs use transflective screens, and you can get a program for the Blackberry that allows the screen to be used as a flashlight (backlight on with white pixels) or a mirror (backlight off with black pixels).

It's possible to add a film to a cellphone or PDA LCD screen that increases light reflection from the surface such that it becomes more of a mirror when the screen is off. For two examples, click here and here. Note, however, the caution at the bottom of the second example's description - after you apply the film you can't use the device outdoors because the mirror effect obscures the screen!

It's also possible to use a different display technology such as OLED (Organic Light Emitting Diode) to solve your problem. A very bright, single-color emissive screen with a reflective top layer can act as a mirror when the screen is off, yet display messages clearly when the screen is on (as long as you aren't in sunlight). Click here for an example of a cellphone that does this. Finally, click here to see another clever but very simple and logical approach to solving your problem.

Based in Silicon Valley, Geoff Walker is Global Director of Product Management at Elo TouchSystems. Prior, he was a consultant with Walker Mobile, LLC (www.walkermobile.com). Geoff has worked on the engineering and marketing of mobile computers since 1982 at GRiD Systems, Fujitsu Personal Systems (now Fujitsu Computer Systems) and Handspring. In addition to mobile computers, Geoff's areas of particular expertise include displays and digitizers.