The difference between lumens and lux - and why it matters

Lux is the measure of the total amount of light that illuminates a surface, described as units of brightness. The closer a light-emitting device is to the surface, the higher the lux will be. Additionally, the brightness exists on a sliding scale: Imagine a dark room and a single light hovering over a table. The light emitted onto the surface of the table is brightest directly beneath the bulb. As you move farther away from that direct point, the lux measurement also decreases.

By contrast, lumens are a measure of the total amount of light generated from a lamp or other light source that is visible to the human eye. Whereas watts measure the energy it takes to power an incandescent light source, lumens tell us the brightness of an LED or halogen bulb.

Re-evaluated measurements

Today’s light bulbs are more energy-efficient than ever before and require us to look at their measurements in a whole new light. In an effort to form and maintain such cutting-edge energy standards, the Australian Government’s Energy Council has implemented the Equipment Energy Efficiency (or E3) Program. This initiative encourages the use of energy-efficient light bulbs that have maximum brightness from minimal energy output.

For example, you can appear to have the same brightness with an old 75W incandescent bulb as you see from a halogen using 52W, a compact fluorescent bulb using about 16W or an LED using just 14W. Therefore, 1,100 lumens would look equivalent to the brightness of that same 75W incandescent bulb.

Due to these new standards, a new point of measurement has also been created to help consumers make the right decision when purchasing these new light sources. The energy efficiency of light bulbs is measured in lumens per Watt (lm/W) – the higher the better.

The measurement of lumens are easy to see in terms of household use, but what about lux? These measurements of light go hand in hand, but lux is the one that can most accurately shed light on the rest of the field.

Practical applications

There are a number of applications where lux measurements are vital – namely, places that need very specific measurements of light. For example, in a modern hospital’s operating theater, the ability to see clearly is vital to a doctor’s success and a patient’s recovery.

The art world would be a different place without the ability to measure lux, as even low light levels – when seen over a long period of time – can ruin everything from oil paintings to cloth tapestries. The damage occurs because light is radiant energy that causes irreversible change, either through radiant heating or photochemical action. The duration and intensity of these potent sources of destructive energies are from just beyond the limits of visible light. Additionally, important documents and other paper content can be impacted by these low light levels as well.

Yet another example is the illuminance recommended when it comes to maintaining an office setting. With more than 80% of information taken in visually by a given company’s staff, the ability to not just maintain adequate light but establish optimum lighting conditions can make a real difference in employees’ lives. For example, the minimum lighting for a task like paint retouching or the colour-matching of dyes requires an illuminance measurement of 800 lumens or more. Similarly, watchmaking and its minute mechanisms require 1600 or more lumens.

Most of us spend more time at work than nearly everywhere else, and an accurate lux measurement can set up the entire workforce for success. The luminous flux per unit area between a light source and the area illuminated by it is measured using the lux meter. To measure these readings efficiently and precisely a photometer is also required, such as those from Testo’s line of Lux Meters.

While the difference between these two measurements are – literally – easy to see, the similarities are also useful when it comes to understanding the full spectrum. To design an optimum plan for every scenario it’s important to understand how these two measurements coincide.

Lumens and lux measurements allow consumers, governments and businesses alike to illuminate a new world full of energy efficient and powerful light sources. They give us the ability to showcase beauty on the wall of a museum as well as help keep office workers healthy.