A signal assembly is provided that includes a chamber defined by isotropically luminant back and side surfaces, and a front surface having a lens and a diffuser. The signal assembly also includes LED light sources having a beam angle ≧70° coupled to the back surface. The back and front surfaces are separated by a depth, and each source is located at a spacing from the other sources ≦the depth divided by a predetermined factor. The predetermined factor may be set to approximately 2.5 or 2.0 when the divergence angle of the diffuser is ≧20° or ≧30°, respectively. The signal assembly and its components can be configured to operate as a vehicular signal lamp.