The difference between Watts and Lumens

A Watt (W) is an International Standard unit of electrical and mechanical power measuring the rate of energy transfer. It can be defined as one Joule per Second.

Watts are named after Scottish mechanical engineer and inventor, James Watt (1736 – 1819), who is renowned for his work in steam engine technology.

All light bulbs have a wattage rating. It follows that the higher the wattage, the greater the amount of electrical consumption or electricity used, thus the more it will cost to run the light bulb.

When incandescent light bulbs dominated the lighting market, it was easy to tell how ‘bright’ a bulb would be. Typically choosing from 150w, 100w, 75w, 60w and 40w bulbs, it was understood that the greater the wattage, the brighter the light.

However, since new low energy lighting technologies such as LED, CFL and Halogen have emerged, vying with one another to be the most efficient; the Watt has been made redundant as a reliable measure of light ‘brightness’.

Take for example the images below, the 60w incandescent, 42 halogen energy saver and 11w energy saving CFL are all equivalent to a traditional 60w bulb with similar levels of ‘brightness.’

To understand how ‘bright’ a light bulb is, Lumens now need to be considered.

Whats the difference between Watts and Lumens

Did you know? 746 Watts = 1 Horsepower!

What is a Lumen?

A Lumen (lm) is the International Standard unit for the total amount of visible light emitted from a source. Like Watts, Lumens are a standard measurement within the lighting industry and can be found on the box of most light bulbs.

To illustrate the relationship between Watts and Lumens across different lighting technologies, consider the following.

The information below shows the typical Lumen levels expected from traditional incandescent bulbs.

  • 40w incandescent = 380 – 460 Lumens
  • 60w incandescent = 750 – 850 Lumens
  • 75w incandescent = 1100 – 1300 Lumens
  • 100w incandescent = 1700 – 1800 Lumens
  • Direct sunlight = 100,000 Lumens

The information below shows the typical Lumen levels expected from LEDs.

  • 5w LED Candelabras = 400 Lumens
  • 7w LED A19 = 600 Lumens
  • 12w LED PAR30 = 850 Lumens

As you can see by comparing the above tables, LEDs are able to produce high Lumen levels with comparatively low wattage consumption. In fact, LEDs are able to produce up to 110 Lumens per Watt, whereas, incandescents only produce 12-17 Lumens per Watt.

Therefore, next time you choose a light bulb, remember to consider both Watts and Lumens. Watts measure the amount of electricity used and Lumens determine the ‘brightness’ of a bulb. The ideal combination being:



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