Kelvin and Lumen: Get to Know the Terminology

April 25, 2014

Kelvin and Lumen: Get to Know the Terminology

The world of lighting revolves around several key terms. When you look at the specs of a light bulbs, various ones pop up. We are all familiar with wattage, but what does a Colour Rendering Index (or CRI) say about the colour temperature of a bulb? And exactly what is lumen? Here’s a quick explanation to help you make sense of them.

What is lumen?

People sometimes assume that the more wattage a bulb has, the more light it gives. Nowadays that doesn’t hold true. Wattage is about how much power a light needs to work. How much light it emits, or to put it another way, how bright a bulb is depends on its lumen value (lm). Lumen is determined not just by how much power (wattage) a light bulb needs, but also by its technology. An LED bulb for example, uses much less wattage than a filament bulb but can produce the same amount of lumen. Be careful though - the fact that some light bulbs are brighter than others does not make them a better buy - it just means they’re suitable for different purposes. A bright LED bulb might be really good for in the kitchen, but would feel far too bright for a bedroom. A filament bulb with less lumen would do better there.



What about colour temperature?

Light bulbs can vary significantly by colour temperature. The colour temperature of a light bulb is to do with how ‘warm’ or ‘cool’ the light is that it emits. The usual measure of colour temperature is the Kelvin scale; this is where the term Kelvin, abbreviated as “K,” comes into play. Up to 3500 K is described as warm white colours, producing a red-yellow appearance. Between 3500K and 4100K is neutral, producing a yellow appearance. 5000K is considered cool, producing a blue appearance as the colour temperature is increased.



So how do I choose the best light bulb?

Let’s recap. The amount of wattage only says something about how much power a bulb uses. Ideally you want to buy a bulb with as low wattage as possible in order to save energy, but this sometimes means you’ll have to compensate on things such as style and CRI.

The lumen value you need depends on what you’re going to use the light for. In the kitchen and above the dinner table, for example, you might want to use a brighter light bulb (so higher lumen value) than for lamps on side tables and in the bedroom.

When it comes to the kelvin the colour temperature scale is the same for all light bulbs. A 3500K incandescent light bulb has the same degree of visual warmth (or coolness) as a 3500K LED or CFL light bulb.


We hope that things have become clearer. If you have any questions left, feel free to pose them underneath this post and we’ll get back to you asap!


(Image 1 viaMassimo Barbieri, image 3 via dteenergy, image 2 & 4 via Fat Shack Vintage)

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