Lighting - The Basics

Measuring Light

Light is measured in lumens and lux.

The 'lumen' is the unit of flow of light, from any one source.

This table shows how much light different light sources give:

one candle	12 lumens
one gas mantle	600-700 lumens
one 100 watt electric bulb	1200 lumens

Thus ten candles give about the same light as a 10 watt bulb and a gas mantle is equivalent to a 50 watt bulb.

The 'lux' measures the amount of light striking a surface. One lux is one lumen per square metre. In the USA, the term 'foot-candle' i.e. lumens per square foot, is used.

For example:

fitting type	range	lux
one low-voltage halogen spotlight with a 35-watt bulb or 100-watt spotlight bulb	3 metres	500	from ceiling to floor
as above	1.5-2 metres	1000	from ceiling to table or desk

A safe minimum for a room is 50 lux.

Glossary

bowl	a ceiling-mounted, upward pointing light with a glass bowl underneath
bracket	wall-light, often swivelling
candelabrum	a branched candlestick or lamp with several lights
candle stick	traditional fitting holding one or more candles
chandelier	pendant from ceiling with three or more arms, lit using candles, and usually decorated with glass crystal decorations
electrolier	an electric chandelier
gasolier	a gas-lit chandelier
lantern	a glass-enclosed light, in house lighting generally hung from the ceiling
pendant	a hanging light with less than three light sources, or otherwise used as a generic name for any hanging light
picture light	a wall-mounted light used in an accent role to illuminate a picture
sconce	a wall-light employing a candle, with an ornamental bracket
uplighter	upward pointing light, usually wall-mounted