Conventional LEDs exhibit a broad spectral width but do not suffer with the electrical driving complexity, temperature sensitivity and optical feedback problems found with the use of lasers. Passively filtering the light from a conventional LED can narrow the spectral width but will always reduce the spectral power density of the output light and would require additional packaging and optics. However a new class of structures, namely Resonant Cavity Light Emitting Diodes (RCLEDs), have been developed in the last few years which appear to overcome several of these issues as well as offering better high-speed modulation performance and efficiency. We have been investigating RCLED's in both the GaAs and InP material systems. The quantum well emitters in both of these systems are chosen such that emission may be through the substrate, i.e. strained InGaAs QW (on GaAs operating around 980 nm) and InAsP QW (on InP operating around 1350 nm). The results demonstrate narrower spectral widths, higher peak spectral power densities and lower temperature sensitivity than nonresonant reference devices grown with nominally the same luminescent region. In this report we concentrate mainly on the GaAs structures. (5 pages)