For example, the plural light beams may have the same or effectively the same wavelength and the same or a similar polarization. Here, effectively the same wavelength means that at least 95% or at least 98% of the energy of the plural light beams is within a wavelength band that spans no more than 30 nm or no more than 20 nm or no more than 10nm - thereby making it impractical and/or inefficient to use a dichroic element to efficiently combine the light beams.