Lux, Lumens And Lighting

Lux, Lumens And Lighting

There are lots of terms that are used when people talk lighting.  The introduction of the LED technology into the lighting domain has turned the traditional thinking of lighting on its head.   Not only has this Comparison have historically been made using lumen output, but the comparison is no longer valid.

How can that be when it has worked consistently for so many years?  What is so different that it no longer works now?

Well, to understand this, it is probably worth spending some time explaining what these words mean.

A lumen is a standard unit of measure of the total amount of light that is produced by a light source.  When thinking of a tradition bulb or globe, if you were to look at it while on (like in the picture), you can see that the light is emitted in full 360 degree directions.  The light source is like the sun with light being radiated in all directions, whether light is needed in that direction or not.

Lux is a standardized unit of measurement of light level intensity, which is commonly referred to as "illuminance" or "illumination".

In summary:
Lumen = total light emitted
Lux = measured light at a specific location.1 lux = 1 lumen/sq-m
Here are some standard lumen comparisons.  Bear in mind, each of these technologies has many wattage options, these are just a few:

LUMENS 3600 8100 1350 12000
WATT 36 60 15 100
LUMEN/WATT 100 135 90 120

Historically, lumen output or lumens/watt have been important measures to understand the relative strength or efficiency of a light source.

It is fair to say that the real reason for invalidating this measure as the only effective means of comparison between a LED light source and a traditional light source is all in the technology.  LED lighting is not traditional lighting.  It is directional in nature and this changes the way we need to think about comparing light sources.  In other words, all of the LED lumen output is used, unlike the wastage from a ‘normal’ globe.

So if lumens are less important, what has taken over as the key consideration?  At the end of the day, the most important dimension in determining appropriate lighting is – lux.  Lux is what defines the effectiveness of lighting…and after all, why have any lighting unless it is effective?

We’ve seen how lumens and lux are related, however, due to a number of factors, it is fair to say that the lumen output of a fitting doesn’t directly translate to the lux on the ground (or wherever else it is needed!)

Given that traditional lighting throws light everywhere, lighting companies have worked hard over the years designing fittings with guards, reflectors, and other features in order to focus the light to where it is needed, seeking to waste as little light as possible.  Depending on the design, these ‘improvements’ have varying impacts on the overall effectiveness of the fitting.  By the same token, LED manufacturers look for ways to spread the light for certain applications.  This again changes the lumen to lux relationship.

So, what does all of this mean?

It’s simple.  As ever, choose your lighting options to suit your needs.  If you are replacing a bulb that is designed to illuminate a room, then look for a bulb with a similar design and lumen output.  This also applied for a LED substitute, however, make sure the light distribution from the LED is also going to illuminate the room in the same way.  There are plenty of LED options here, and it isn’t hard to find a substitute.

BUT – if you are looking to create a design that is compliant with a specific standard, such as a sports field, car park or office, you need to understand the requirements of that standard in terms of lux levels.  From there you can create a design that works for that application.  Lumen output is immaterial as long as the lowest lux levels (and other parameters) are achieved.  This is validated by understanding the light distribution of the light source and is best confirmed with a design.

As you can see from these simple examples, there are very different comparisons depending on what the lighting requirements are.

Hopefully now you will have a better appreciation of this lighting jargon and you will feel confident in handling your lighting needs.