an instrument and method for curing light - curable compounds in the mouth of a patient , the instrument comprising a housing and a plurality of solid state , light - emitting elements on a substrate supported by the housing . the elements form a collective array on the substrate operable for collectively emitting light having wavelengths within a narrow band of wavelengths . an optical focusing device is positioned to intercept the light emitted by the array of elements and includes a non - imaging optical device which is operable for collimating the light from the array into a beam to be directed onto a compound for curing the compound . a disposable sleeve covers the housing and array and may incorporate the optical focusing device . the sleeve is removed and discarded after use to eliminate the need to autoclave the instrument .