A tissue illumination apparatus is useful in identifying caries, calculus, fractures, diseases or other defects in tissues within the oral cavity. The tissue illumination apparatus includes a light emitting device and at least one focusing lens. The lens may be configured to be integrally or releasably attached to the light emitting device. The tissue illumination apparatus may optionally include one or more intermediate focusing lenses. The fluorescing lens and/or any intermediate focusing lenses are made from any desired material that may be impregnated or coated with one or more fluorescing compounds and/or one or more light-absorbing dyes or pigments. The fluorescing lens converts light emitted by the light emitting device into light having a longer wavelength in order to transilluminate oral tissues and render certain dental tissues and/or defects therein visible to a dental practitioner.