Lighting Fixture Parts Explained

Fluorescent fixtures differ from halogen fixtures that differ from metal halide fixtures, but they all have several lighting fixture parts in common. The fixture provides the physical support, electrical connection, and light control for an electric lamp. Here is the breakdown.

Housing
It is the electrical connection and physical support for the light source. They are divided into 5 categories.

1. Recessed – mounted above the ceiling and hidden entirely from view with only an opening in the ceiling plane to allow light to pass through. With fluorescent, metal halide or low voltage fixtures the ballast or transformer may be in the housing making the whole unit larger.
2. Semi-recessed – mounted partially above the ceiling with the remainder of the finished fixture visible from below. With fluorescent, metal halide or low voltage fixtures the ballast or transformer may be in the housing making the whole unit larger. 
3. Surface-mounted – mounted to the surface of a ceiling, wall or in rare cases a floor. The junction box is recessed into the mounting surface giving it a cleaner appearance. 
4. Pendant mounted- the luminaire is separated from the ceiling by a stem, chain or cord. The junction box is also recessed into the ceiling giving it a cleaner appearance.  
5. Track mounted – a recessed, surface mounted or pendant mounted track provides both physical support and electrical connection through an adapter on the luminaire.  With low voltage and metal halide track heads, the transformer is usually attached to the fixture head.

Light controlling element
Reflectors are beam control devices that take many forms that its main uses is to direct the light into a particular direction. In case of a downlight, it’s to efficiently direct it downward. Specular aluminum reflectors produce the most efficient beam control. Semi-specular reflectors are slightly less efficient but they eliminate the irregularities in the lamp beam ore reflected images of the filament coil or lamp phosphors, in the case of compact fluorescent. You can find reflectors in downlights, linear slots, troffer-type fixtures, wallwashers, strip lights etc.

Glare control element
Shielding material is a critical component because this element is most prominent in the direct field of view. The purpose of diffusers, lenses, louvers, reflectors and other shielding materials used in fluorecent downlight fixtures is to redirect light from the glare zone towards work surfaces. There are several different kinds. Prismatic lenses incorporate a pattern or prisms or other refracting elements to reduce the brightness of the luminaire and inhibit direct glare.
Egg-crate louvers made of intersecting straight –sided blades reduce luminance by blocking light rays that otherwise would emerge at glare angles.
Parabolic louvers control luminance precisely by using multiple cells with parabolic reflectors and a specular or semi-specular finish.

This is just a general specification of the fixture components. Each particular fixture, whether it be fluorescent, incandescent, low voltage, LED or metal halide has specific components to it, depending on its source and function.