These lenses come in a wide variety of sizes and thicknesses, both in standard ceiling size, and fabricated to fit your specific application. Lenses refract light so that most of the light is directed downward, some of it is refracted into the higher angles. Prismatic lenses will display more of the light source's brightness than specular parabolic louvers. This additional brightness will tend to brighten the ceiling and upper portions of adjacent walls. Lenses are most appropriate when brightness and economy are desired and where visual tasks are not being compromised.