Light collectors for use in building-integrated solar concentrators comprise waveguiding components incorporating spaced-apart light collecting elements arranged to collect light from a plurality of lenses in a lens array and deliver light to solar cells for photovoltaic conversion, where several lenses are coupled to each individual solar cell. The light collecting elements may comprise shaped ends of bulk waveguides to deliver incident solar radiation directly to the solar cells, or luminescent or amplifying material that converts the incident radiation to a secondary light signal that is delivered to the cells. The lenses may be pivotally mounted in a variety of ways to improve solar tracking by avoiding mechanical clashes between lenses and optimising the amount of incident light that is harvested. Filters containing heavy water may be positioned in front of the solar cells to absorb long wavelength light unconvertible by the cells, heat energy being then extractable from the heavy water.