This is part 6 of the Windows Phone 7 series:
Resolution and orientation considerations
As you may know, there will be two screen sizes for Windows Phone 7 – the “small” screen and the “large” screen. The resolution of the “large” screen will be 480x800 pixels, while the resolution of the “small” screen will be 320x480 pixels. It will be great if we can write our programs to work on both of the resolutions(screens). In theory this is possible, but if you try to do it, you’ll find, that it’s not always possible, even if you use different XAMLs for both of the resolutions.
The greatest denominator of 800, 480 and 320 is 160, so we can visualize the screens as 160 pixels squares.
Keep in mind that the user can rotate the screen to put it in a landscape mode. Of course, your program may require the screen to be in a specific orientation mode. If you choose to support both landscape and portrait orientations, you should know that there are events for detecting the orientation changes and some orientation shifts are automatically handled in Silverlight.
The aspect ratio of the small screen is 3:2, while the aspect ration of the large screen is 5:3. As you may have noticed, none of the screen’s aspect ratios matches the TVs aspect ratio, which is 4:3 for standard definition and 16:9 for high-definition.
Display Considerations
Just like Zune HD and a lot of other phones recently, Windows Phone 7 devices will use OLED(organic light emitting diode) displays. Unlike the old flat displays, power consumption in OLED technology is directly proportional to the light emitted from the display.
OLED displays are double-edged sword, if you don’t know the technical details of the technology. OLED displays consume half of the LCD power, but only when the screen is mostly black. If you use white for your basic color, it is possible for the OLED screen to consume up to three times more power than the LCD.
Keep in mind that what we are talking about is a phone, and everybody should know how important the battery for the phone is. That's why we should make the design of our programs mostly with dark colors. And that is why in the default Windows Phone 7 style, backgrounds are black.
There is one phrase you should keep in mind, when you write Windows Phone 7 applications: “Black is beautiful”.