A recessed light or downlight (also pot light in Canadian English, sometimes can light [for canister light] in American English) is a light fixture that is installed into a hollow opening in a ceiling. When installed it appears to have light shining from a hole in the ceiling, concentrating the light in a downward direction as a broad floodlight or narrow spotlight.
There are two parts to recessed lights, the trim and housing. The trim is the visible portion of the light. It is the insert that is seen when looking up into the fixture, and also includes the thin lining around the edge of the light. The housing is the fixture itself that is installed inside the ceiling and contains the light socket.
The earliest recessed lights were developed around the early 1940s.
In North America, recessed housings generally fall into one of four categories.
The main purpose of the housing is to ensure that no flammable materials come into contact with the hot lighting fixture. Badly-housed downlights can be a fire hazard, though all newer ones contain a thermal reset switch for safety.
Recessed lighting styles have evolved with more manufacturers creating quality trims for a variety of applications. You can find recessed lighting trim with the standard baffle in black or white, which is the most popular. They are made to absorb extra light and create a crisp architectural appearance. There are cone trims which produce a low-brightness aperture. Multipliers are offered which are designed to control the omni-directional light from "A" style incandescent light bulbs and compact fluorescents. Lens trim is designed to provide a diffused light and protect the lamp. Lensed trims are normally found in wet locations.
The luminous trims combine the diffused quality of lensed trim but with an open down light component. Adjustable trim allows for the adjustment of the light whether it is eyeball style, which protrudes from the trim or gimbal ring style, which adjusts inside the recess. These lights allow for full versatility. Lastly, there are the wall-washer trims, which are designed to eliminate the often seen "scalloped light effect".
There are two types of light bulbs for recessed lighting: directional and diffuse. Directional lamps (R, BR, PAR, MR) contain reflectors that direct and control the light. Diffuse lamps (A, S, PS, G) control light distribution through their omni-directional light.