If you want to compare the relative ‘brightness’ of two light-sources – a traditional halogen bulb vs a metre of LED tape, for example – then the two lumen figures will give you the comparison you need.
But if you need to know how brightly a floorspace or other surface area will be lit, then lumens aren’t the right measure. Instead, you should use lux.
Lux values provide a means to measure ‘illuminance’ – which is the intensity of light falling on a particular area. One lux is defined as the illumination that will light a surface one metre from a single candle, which is to say, it’s the light produced by one lumen over an area of one square metre.
The lux value of a light-source on a surface is affected by the source’s beam-angle and its distance from the surface being lit.
- A narrow beam will light a smaller area more brightly, while a wider beam will light a larger area with less intensity;
- A light-source close to the surface being lit will light a smaller area more brightly, while a more distant source will light a larger area with less intensity.