Lumen and wattage

Lumens are mainly used to determine the intensity of light from a bulb. A higher lumen count always indicates a higher amount of light.

A watt is a unit of power consumed by a bulb to produce light. The higher the wattage of a light bulb, the brighter the light is usually. A 12 W bulb will burn much brighter than a 6 W bulb.

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Luminous flux, or lumen output, is a measure of the light output of a luminaire. In other words, it indicates the luminous intensity of the luminaire. The higher the lumen value, the higher the luminous efficacy of the bulb, and vice versa. The exact figure is given by the manufacturer, as the specification is influenced by factors such as the shape of the lamp body, colour and other factors affecting the reflection of light.

The lumen is the best indicator of the overall luminous efficacy of the lamp.

Lumens (abbreviated lm) therefore indicate the total visibility to the human eye of light from any light source.

Exactly how many lumens are needed to say that we are in a well-lit space? Such an accurate reading can be told according to the intended use of different spaces. The number of lumens depends on a number of factors, such as the shape and size of the room, the height of ceilings, the needs of the person and the type of light source (shade, direct, indirect).

Basic amounts are defined by various sources as per 1 square metre. In this respect, the size of the room is therefore the determining factor. Different rooms in the home require different levels of lighting. The kitchen requires 400 - 500 lumens per square metre, while the bathroom (where make-up is applied) can be considered for 600 - 800 lumens per square metre.

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People usually buy each luminaire according to its wattage. But why? People are quite conscious of buying lamps after looking at the wattage, as this has been easy when only incandescent lamps were available as a technology. The higher wattage of a lamp meant it was brighter. Because in the days of incandescent light bulbs, everyone knew that the amount of light (and heat) was directly related to the watts.

A watt is a unit of power that can be used to determine the energy consumption of a light source, kWh.

The Led confuses this equation dramatically. What we have learned in the past no longer holds true in the same way. Watts still describe the power input of a light source, and LED lamps are now more efficient and do not consume as much energy, thus reducing the size of the electricity bill. But the light output per watt varies across LEDs.

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Lumen (lm) is the standard unit for luminous flux. It can be expressed as the amount of luminous flux from a light source to an area in a unit of time. In contrast, the watt is a typical unit of electrical power. It is measured in joules per second (j /s).

Lumens / Watts = luminous efficacy