...which type of digit technique should be deployed. There are reflective LCDs or self-lighting LED elements available, just to tell about two basic techniques which can be used to show digit numbers in 7-segment-code.
There are various differences: The surrounding light at the place where the display should be installed is a basic criteria. In general we recommend reflektive LCDs for a very bright surrounding, especially for outdoor application. Selflighting LEDs are typical for an indoor situation with moderate light.
Depending on the deployed digit technique there are different digit heights available, which are listed in the particular sections which follow. As an example, mechanical digits are gaining on applications where very huge digit elements are wanted. These digits should be legible from large distances.