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Lumen, lux, wattage and kelvin - what are they and why does it matter?

Lumen, lux, wattage and kelvin - what are they and why does it matter?

Lumen, lux, wattage and kelvin are potentially the terms most misunderstood by first time LED lighting buyers.

At first, the terms can appear interchangeable, and so are often mentioned in conversations about LED lighting. But, they are 4 distinct terms with 4 entirely different meanings.

So what do they actually mean?

Wattage (w): The amount of electrical power used to run equipment

Lumen (lm): The amount of light emitted from a light source

Lux (lx): The brightness of a room

Kelvin (k): A measurement used to describe the color temperature of a light source

So that’s the basic explanation. And these are the most important things to know about this terminology when you’re considering a lighting upgrade.

1 - The wattage of a light tells you how much it costs to run, not how much light it will generate.

So, the higher the wattage, the higher ongoing cost as it will consume more energy. It’s obvious that a 200 watt light will use double the energy of a 100 watt light.

But what’s not obvious is how bright each of those lights are. Just because one has double the wattage, does not mean it will be twice as bright.

2 - The lumen output of a light is a direct, and universal measure of the light output of a fitting.

The higher the lumen, the more “pieces of light” the fixture emits and the brighter it will make the room.

3 - The wattage and lumen output are not directly linked.

Just because you have a high wattage light, it does not mean you will have high light output.

For example, a 150 watt fitting could emit the same amount of light (lumen) as a 100 watt fitting. But, the 100 watt fitting will cost less to run, all other factors remaining the same.

Consider that two years ago a top of the range 60 watt LED linear fitting may have output 4,000 lumens (pieces of light). Whereas today, UrbanVolt’s equivalent 60 watt outputs almost 8,000 lumens.

The efficiency of both the wattage and light output is called the lumen per watt ratio (lm/w) and is a measure of the efficiency of a light fitting.

So, when someone says they need a 100 watt fitting to make their warehouse bright enough, that’s incorrect. Because it’s not the wattage that will light the warehouse, it’s the lumen output.

4 - Lights range in colour from warm and romantic, to clinical white.

Depending on your business, you will want the light to be ‘yellow’ or ‘white’ or somewhere in between.

The term for this colour temperature is kelvin.

Ironically, the higher the kelvin, the ‘colder’ the light.

For example, a very white light - which would be used in a hospital theatre - will have a kelvin of 5,000+.

A colour temperature of 2700–3600 K is generally recommended for most general indoor lighting. However, speciality and complex manufacturing will require a much higher kelvin.

5 - What people are usually referring to when they talk about their ‘required lumens’, is lux levels.

Lumen output is the amount of light which a light fitting generates. But the lux level is the level of light on the ground.

For example, a 150 watt light may have a high lumen output, but if it is at a height of 25 metres, it may not be delivering enough light at ground level.

The lux level is measurable (via a lux meter) and this measure factors in the lights above your head, the sunlight shining in through the windows, the shape of the room and the various obstructions to the light bouncing around the room.

It is lux levels which are truly important when making a decision on LED lighting. Many businesses have minimum required lux levels to be achieved for the work they are doing - from office work, to painting aeroplanes, to making tiny little chips for computers. When we hear ‘minimum lux’, we first determine the lumen output we need to achieve that brightness level on the ground. And then we deliver that light output with the lowest wattage fitting so that the LED lights cost less in the long run.

In summary, the brightness of a room (lux) will be increased if the lighting in the room has a higher light output (lumen). The amount of energy they use (wattage) will be reflected in your ongoing energy bill.


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