Backlighting can be incorported within Membrane Switch Panels, Keypads and Keyboards. Normally to enchance the appearance of the product OR in applications where the ambiant light is low.
Intraaction Electronics are developing the following options.

Surface mount LED's are incorporated using conductive epoxy and can provide selective backlighting. LED's are efficient and do not radiate heat.
Various type of LED's can be incorporated "low profile" "side emitting" "dual emitting" and others.
IntraAction can offer various options.
The use of optical fibers carring light along the lengths of fibers provides uniform lighting in required areas. The actual light source can be one LED or several LED's.  Again as the light is LED, they incorporate the long life and low heat feature.
IntraAction Electronics can offer variouse options.

EL backlighting, uses a printable ink embedded with light emitting phosphors.  This type of backlighting provided possible the best type of backlighting but has disadvantages such as higher in cost than LED options and requires a  higher voltage. IntraAction Electronics can provide variouse options.