Integrating spheres are proposed as light-confining cavities for enhancing the absorption of light by devices such as solar cells, and also for making photovoltaic converters with cells of several band gaps. A new concept for achieving this light confinement by angular restriction of the escaping of rays, which avoids the requirement of having a small entry aperture and therefore concentrations on it that are much higher than those required on the solar cells, is proposed here.