General downlights use various optical devices to control light distribution including: reflectors, cones, baffles, and diffusers.
Reflectors are used primarily with A lamps and combine the optical characteristics of two geometric shapes, a parabola and ellipse. A parabola directs light straight down. An ellipse directs the light to a point just below the fixture and then spreads it out from that second point. This combination distributes light in a uniform spread.
The reflector combined with an A lamp or low wattage HID lamp provides an excellent balance between efficiency and light control making it the most popular downlight. The open reflector is available in different finishes: white, clear alzac, or gold alzac.
PAR and low voltage lamps have their own internal reflectors and may be selected with either flood or wide spread beam distribution.
A bare lamp hanging down from the ceiling can produce an annoying glare. Recessing the lamp above the ceiling reduces direct glare but also reduces light output. Cones were designed to overcome this problem. Cones are parabolic in shape and act as a continuation of the lamps internal reflector. They're generally specified when low brightness is important. Cones provide a narrower distribution of light than a standard reflector, and they're normally used in applications with higher mounting heights.
Cones are made from an alzac material and are available in three finishes. The clear cones provide a crisp, bright appearance while gold adds a warmer tone. Black creates a very low brightness, dark hole effect. Each type of cone has distinct reflective characteristics that affects the overall efficiency of the lighting system.
Another means for controlling overall fixture brightness is the baffle. Baffles are straight sided sleeves with V shaped grooves. They reduce glare by absorbing a significant portion of light and are used with A, PAR, and HID lamps. Overall fixture efficiency is sacrificed in favor of ambiance and brightness control.
A diffuser is the fourth optical control that uses a lens to hide the lamp and redirects the light emitted from the fixture. The position of the lens also impacts the overall appearance. For example, a drop lens emits more light into the space but also increases the brightness of the ceiling. A flush lens reduces brightness while reducing overall efficiency. A lens recessed above the ceiling plane with a splay provides the best brightness control for opal lenses. The fresnel produces a controlled spread of light using clear etched glass with concentric circles. Other diffusing lenses include the concave, tempered prismatic, and drop opal.