Simply put, lumen (lm) measures the brightness of a light source. The unit indicates how much light a lamp emits - in all directions. The higher the lumen value, the more light a lamp emits per unit of time.
Whereas with conventional light bulbs the brightness could be determined on the basis of the power consumption in watts, nowadays the lumen value is decisive when buying a lamp. While watts measure power consumption, lumens provide information about the visible light emitted by a lamp.
Luminous efficacy: lumens per watt
The efficiency of a lamp is measured in terms of luminous efficacy (lumens per watt). This value describes how much of the required energy is converted into light. In other words, the higher the value, the more efficient the luminous efficacy.
Tip: The lumen values of different lamps can simply be added together. For example, you can easily replace old lamps with efficient LEDs without losing brightness. You simply add up the values of the old lamps and provide adequate replacements.