Non-imaging radiation collecting and concentrating devices, and assemblies, are disclosed. The non-imaging radiation collecting and concentrating devices comprise an entrance aperture for receiving incoming radiation, an exit aperture located opposite to the entrance aperture for outputting concentrated radiation, and one or more concaved reflectors arranged between the entrance and exit apertures. The concaved reflectors define an acceptance angle of the device relative to an optical axis thereof and configured such that their optical focuses are located between edges of the exit aperture and the optical axis, thereby substantially preventing escape of the incoming radiation received in the entrance aperture within the acceptance angle and providing substantial uniform radiation collection at the exit aperture of the device.