What is a Lumen?

A lumen is the standard for measuring the total amount of visible light given off by a source.  It is the SI derived unit of luminous flux and has been the standard of measuring non-directional lighting for as long as we can remember.  More recently however, the lumen has made a resurgence, mainly due to the new way of classifying LEDs set out by the EU and it is because of this that the majority of the population simply do not understand it and this article should help understand the complications of 'Lumens'.

If you cast your mind back a few years, before the existence of LEDs, you would probably know in your mind how bright a 25W, 40W and 60W light bulb was.  This is because there wasn't really much else to choose from.  Granted there were car bulbs and torch bulbs but not really much else.

Unfortunately because there was no real policing, the manufacturers cut corners in the race to the highest profit.  Sub-standard filaments were being used, poor cap paste, the wrong gas, the list goes on.  Only when you looked at the difference between 4 or 5 manufacturers and the lumen values did you really see who was best and who wasn't measuring up, however all would list for example 40W on the light bulb and the manufacturers didn't have to state this lumen value anywhere on the product or literature associated with the product, for this reason we just don't understand lumen on light bulbs.

Fast forward to the current year, and manufacturers have to put every value possibly associated with the light bulb on the box and on the packaging and boy, is this confusing.  Now lumens is everything, in order for an LED to claim an equivalent wattage, the LED bulb must output a specific lumen value and that is why there are strange values to the lumens and not numbers to the closest 100 or 10 even.

The following table lists the lumen values and the equivalent wattages (this is for non-directional lights only, so not spotlights):

 Equivalent Wattage Value Lumen Value the LED Bulb must be
15W 136 lm
25W 249 lm
40W 470 lm
60W 806 lm
75W 1055 lm
100W 1521 lm
150W 2452 lm


The EU dictates to manufacturers that the lumen value must be 2 times the size of the wattage on the light bulb now, and this is why you see a large random number on the front of LED packaging.  This is definitely a really good thing as it makes sure that the standard of LEDs is kept high because there was a time that it was certainly dipping and a lot of websites popped up with poor quality LED bulbs and it started to give LEDs a bad reputation when they certainly didn't deserve it.

Directional lights, for example spotlights and GU10s, are a different kettle of fish altogether and their light is measured in 'Useful Lumens'.  Click the link below to find out more about useful lumens:

Useful Lumens Guide

Here at LEDSmiths, we will only sell you an LED bulb that is the equivalent wattage that you need.  If it says 40W equivalent on the website, it is a 40W equivalent in the box.

Try our free lumen to wattage calculator below to find out what your LEDs lumen value works out in old wattage equivalence: 

Lumen to Equivalent Wattage Convertor
What LUMEN value would you like to convert? (number only)
Click the following button to convert into an equivalent wattage:
The Equivalent Non-Directional Wattage is:


If actually you need to find out what LED lumens you need from a wattage of bulb that you have then use our Equivalent Wattage to Lumens calculator instead: 

Equivalent Wattage to Lumen Convertor
What WATTAGE would you like to convert? (number only)
Click the following button to convert into the correct lumen value:
The LED Lumen value is:


If you have any questions on lumens or the article above then please don't hesitate to get in touch with us through our details on the "contact us" page.