{"id":202,"date":"2025-12-12T11:16:27","date_gmt":"2025-12-12T11:16:27","guid":{"rendered":"https:\/\/blog.lyco.co.uk\/blog\/?p=202"},"modified":"2026-03-27T13:52:52","modified_gmt":"2026-03-27T13:52:52","slug":"lumen-lux-candela-an-introduction","status":"publish","type":"post","link":"https:\/\/blog.lyco.co.uk\/blog\/lumen-lux-candela-an-introduction\/","title":{"rendered":"Lumen, Lux & Candela – An Introduction"},"content":{"rendered":"\n
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Posted on 30 December 2013<\/p>\n\n\n\n

Author: Charles Barnett<\/p>\n\n\n\n

Last updated on 29 July 2021<\/p>\n<\/div>\n\n\n\n

Lumen (lm), lux (lx) and candela (cd) are units of measurement used to describe the output of\u00a0bulbs<\/a>\u00a0and\u00a0light fittings. With incandescent and halogen lighting it was always easy to equate wattage with light output, because the same wattage always produced the same amount of light.<\/p>\n\n\n\n

Now that different technologies have entered into the equation, using wattage as an indicator of output has become increasingly obsolete. In retrofit CFLs or LEDs, and even energy-saving halogen lamps, an equivalent incandescent or halogen wattage is given by manufacturers to make life easier.<\/p>\n\n\n\n

Like-for-like comparisons between modern light sources are complex, since their output per watt varies considerably from one product to the next. Therefore, more universal units of measurement are required \u2013 measurements that actually record light.<\/p>\n\n\n\n

Lumen, lux, and candela are definable as follows:<\/p>\n\n\n\n

Lumen (Lm)<\/h2>\n\n\n\n

Lumens measure the total amount of light energy from any source, regardless of direction. The lumen answers a simple question: how much light does this source produce?<\/p>\n\n\n\n

When buying modern bulbs you\u2019ll find the lumen measurement added to the packaging and stated prominently \u2013 usually at twice the size of the wattage.<\/p>\n\n\n\n

Lumens are used to measure energy efficiency, using a lumens-per-watt formula. In the lighting industry this formula is called \u2018luminous efficacy\u2019. Efficacy refers to a ratio between two different units of measurement.<\/p>\n\n\n\n

Sometimes lighting manufacturers give a \u2018LOR\u2019 measurement (Light Output Ratio), which accounts for the percentage of light in lumens wasted between the source and transmission through a light fitting.<\/p>\n\n\n\n

A guide to the energy efficiency (or luminous efficacy) of various technologies is as follows:<\/p>\n\n\n\n