A system to provide radiant energy of selectable spectral characteristic
(e.g. a selectable color combination of light) uses an optical
integrating cavity to combine energy of different wavelengths from
different sources. Sources of radiant energy of different wavelengths,
typically different-color LEDs, supply radiant energy into the interior
of the cavity. The cavity has a diffusely reflective interior surface and
an aperture for allowing emission of combined radiant energy. Control of
the intensity of emission of the sources sets the amount of each
wavelength of energy in the combined output and thus determines a
spectral characteristic of the radiant energy output through the
aperture. A variety of different elements may optically process the
combined light output, such a deflector, a variable iris, a lens, a
variable focusing lens system, a collimator, a holographic diffuser and
combinations thereof. Such systems are useful in various luminous
applications as well as various illumination applications.