US Patent 7354179 Prism set and light emitting apparatus using the same

A prism unit includes a first prism having a first incident face and a first refraction face that is adjacent to and that cooperates with the first incident face to define a first angle ranging 50° to 70°, a second prism having a second incident face that is generally parallel to the first refraction face and a medium layer sandwiched between the first refraction face and the second incident face, and having a refractive index smaller than that of the first and second prisms.