Lumen – unit of luminous flux

9/15/2025 #From the World of Lighting

When choosing a light bulb or LED lighting today, we usually no longer focus on power consumption in watts, but rather on the value in lumens (lm). This term has become a common part of specifications and marketing materials from lighting manufacturers. But how did it originate and why is it used?

What does lumen mean?

The word lumen comes from Latin and means “light” or “radiance.” Within the International System of Units (SI), lumen represents the unit of luminous flux.

Formally, it is defined as follows:

1 lumen is the luminous flux emitted by a point source with a luminous intensity of 1 candela, radiating uniformly into a solid angle of 1 steradian.

In other words, a lumen expresses how much light a source actually emits into space, within the spectrum perceived by the human eye.

Historical development and the reason for its introduction

For a long time, light bulb performance was expressed in watts – for example, a “60 W bulb.” However, a watt is a unit of power consumption, not the amount of light. With the introduction of energy-saving fluorescent lamps and LED lighting, which produce much more light at lower power consumption, it became necessary to find an objective and comparable unit. This became the lumen, as it directly describes the light output perceived by humans, not the energy consumed.

Lumen does not carry a personal name

Unlike units such as ampere, watt, or tesla, which are named after notable scientists, lumen is named neutrally – from the Latin “lumen” (light). The name was chosen by the International Committee for Weights and Measures (CIPM) as a clear and symbolically accurate term for luminous flux.

How to imagine lumen in practice

For better orientation, here are approximate luminous flux values of common light sources:

How we use lumen on the Solight e-shop

On the Solight e-shop (solight.cz/en/e-shop), you can find a filter on the left side within each category that allows you to search by luminous flux (lumens). This makes it easy to find a product with exactly the level of lighting you need – without complicated calculations.

Examples of products with the highest luminous flux on the Solight e-shop:

Preview	Product	Luminous flux (lm)
	Solight high bay, 240W, 33600lm, 120°, Philips, MW, 5000K, UGR<25, LM80, DALI	33,600 lm
	Solight linear high bay	19,500 lm
	Solight LED connectable linear lighting	4,750 lm
	Solight LED linear tube	3,080 lm

Conclusion

Lumen has become a practical and universal indicator because it directly answers what we are actually looking for when choosing lighting: how much light we get. It represents an elegant combination of scientific accuracy and linguistic tradition – and a reliable tool when selecting lighting.