This paper presents an efficient, low-cost, versatile LED-based light simulator intended to produce a well-characterized spectrum for tests of solar cells and other photosensitive devices. Three major design aspects are addressed: LED spectra, power converters for LED drive, and control. Visible light emulating a standard solar spectrum is used as a test application using six LED colors. The number of LEDs and their placement for uniformity are addressed. Independent control of the six colors can simulate a range of different light sources and solar spectra. Boost converters under current-mode control are used to achieve reproducible LED brightness through adjustable currents, or equivalent radiant flux commands. Spectral uniformity tests verify that the system achieves standard uniformity requirements over an area of 100mmx100mm in simulations, and 100mmx50mm in experiments. The system is much less costly than available spectral test equipment. Current-mode controllers successfully maintain the desired illumination commands with low steady-state error and ripple, at converter efficiencies exceeding 93%.