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High-Bay Lighting

Definitions

Ballast

A voltage-current controller required to provide the electrical conditions needed to start and operate a discharge lamp.

Colour rendering index (CRI)

The colour rendering index (CRI) describes the effect of a light source on the colour appearance of objects, compared with a reference source of the same colour temperature. It serves to distinguish quality differences between light sources that emit light of the same colour. The highest CRI value attainable is 100. Typical cool white fluorescent lamps have a CRI of 62. A value of 85 or higher is preferable in areas where people work with colours.

Fluorescent lamp

A low-pressure mercury discharge lamp.

HID (high-intensity discharge) lamp

This class of lamps includes high-pressure sodium, mercury vapour and metal halide lamps. All HID lamps have an inner arc tube within another tube. Of these three types, metal halide lamps are the most common choice for interior lighting because they have the best colour rendering. Low-intensity discharge lamps are better known as fluorescent lamps.

High-bay space

Generally, these are spaces with at least five metres and, more often, at least seven metres of clear height. High-bay spaces are widely used in warehousing, big box retail and manufacturing.

High-pressure sodium lamp

A type of HID lamp filled with sodium vapour. These are more efficient than metal halide lamps but have poorer colour rendering.

HO (high output)

A standard T5 lamp is a 32-watt lamp with a rated output of 2900 lumens; a T5 HO lamp is rated at 54 watts and produces 5000 lumens at 35°C.

Lamp

The lighting industry term for a bulb.

Lumen

The flux of light being produced by a light source or received by a surface. The intensity of a light source is measured in candelas. One lumen represents the total flux of light emitted, equal to the intensity in candelas multiplied by the solid angle in steradians [1/(4×pi) of a sphere] into which the light is emitted.

Lumen maintenance

A measure of how well a lamp maintains its brightness over time.

Lumen maintenance = light output of a lamp at 40% of its rated life
                                        light output when new

Luminaire

A complete lighting unit (or fixture) that consists of lamp(s) and ballasts(s) with parts for reflecting light into the space to be lit and for connecting the lamps to the power supply.

Metal halide lamps

A type of HID lamp filled with metal halides in addition to the argon and mercury used in mercury vapour lamps. Metal halide lamps provide improved performance over mercury lamps.

Mercury vapour lamps

An argon and mercury-filled HID lamp. These are less efficient and have poorer colour rendering than metal halide lamps.

T5, T8, T12

Shapes and sizes of fluorescent lamps. "T" refers to shape (tubular), and the number refers to the diameter of the lamp in eighths of an inch.

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