Why LED Lights Are Measured in Lumens and Not Watts

The lighting industry is changing the way we pick and choose our light bulbs. As of the 1st September 2010, it has become mandatory for all lighting equipment within the EU to be labelled in terms of lumens, instead of watts.

For years, we have shopped for light bulbs based on their wattage. With the arrival of energy saving light bulbs on the market, this terminology has become redundant.

Watts are only able to tell us how much energy a light bulb uses and nothing about the type or amount of light given out.

LED Lights use a tiny amount of power compared to halogen and fluorescent bulbs, while producing the same amount of light. This makes it difficult to gauge their performance using watts and even harder to draw comparisons.

What are Lumens?

Lumens are a measurement of the total amount of visible light emitted from a source.

One lumen is about the same as the amount of light given off by a single birthday candle at a distance of one foot from the observer. A light bulb that produces 1 lumen of light will therefore be as bright as that birthday candle. An 100 lumen light bulb will be as bright as 100 birthday candles perceived from a distance of 1 foot.

Lumens per Watt

The efficiency of a light bulb is expressed in lumens per watt (lm/W), also known as its lumen-to-watt ratio. When we talk about lumens per watt, we are measuring how many lumens of light are produced for each watt of electrical energy consumed.

Naturally, if a light bulb produces a greater number of lumens and consumes fewer watts, it is more efficient. The most efficient incandescent light bulb will only produce about 17 lumens per watt. CFLs (Compact Fluorescent Lamps) are slightly more efficient, and will run at between 35 and 60 lumens per watt.

LED Lights exhibit far more impressive figures. A typical LED will easily manage a light output of 160 lumens on a single watt. However, some of the most advanced LED Bulbs are already achieving the legendary 200 lumens per watt predicted by Haitz's Law.

As LED Lights produce more light while using less energy, they are more cost effective to run. As well as saving money, this also means they are helping our environment by reducing CO2 emissions.

Equivalent Incandescent Wattage

Not everyone is versed in the language of lumens and, recognizing this, most light bulb retailers will include an 'equivalent incandescent wattage' to simplify matters. In short, this tells the customer the wattage of the incandescent or halogen bulb the LED is designed to replace.

So, for example, the actual wattage of a GU10 LED may be 4 watts, but its equivalent incandescent wattage will be 60 watts, as it produces enough light to replace a 60 watt halogen.