Grating

A grating is any regularly spaced collection of essentially identical, parallel, elongated elements. Gratings usually consist of a single set of elongated elements, but can consist of two sets, in which case the second set is usually perpendicular to the first (as illustrated). When the two sets are perpendicular, this is also known as a grid or a mesh.

Grating can also come in 4 feet (121.9 cm) or 2 feet (61 cm) x 8 feet (243.8 cm) which are often used for decks on bridges, footbridges and catwalks. Other panel sizes may also be available. Grating can be made of different materials like steel, aluminum, fiberglass. Fiberglass grating is also known as FRP Grating.

A grating covering a drain (as illustrated) can be a collection of iron bars (the identical, elongated elements) held together (to ensure the bars are parallel and regularly spaced) by a lighter iron frame. Gratings over drains and air vents are used as filters, to block movement of large particles (such as leaves) and to allow movement of small particles (such as water or air).

Grating can also be a diffraction grating: a reflecting or transparent optical component on which there are many fine, parallel, equally spaced grooves.

A grating can also be a picture having the characteristics of a grating. For example, a picture might be of a collection of parallel black bars separated by equal-sized white bars. These sorts of gratings are described by a graph (illustrated). On the y-axis of the graph is the luminance obtained by moving a light meter over the grating perpendicular to the orientation of the grating. On the x-axis of the graph is the distance the light meter moved. The example is a square-wave grating (see second panel of the illustration); the graph consists of flat, low lines (corresponding to the black bars), with abrupt corners leading to flat high lines (corresponding to the white bars). One period (or ) of such a grating consists of one black bar and one adjacent white bar. Gratings where the black bars have a different width from the white bars are rectangular and are described by the duty cycle. The duty cycle is the ratio of width of the black bar to period (or pitch, i.e. the sum of the widths of one black and one white bar).

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