Luminous flux is the measure of the amount of light a light source emits in all directions, and is expressed in lumens (lm) . It's a key metric for understanding how much light a light source actually produces, regardless of the direction in which it's emitted. Luminous flux is therefore a quantitative representation of the total light output of a lamp or lighting source.
What is luminous flux?
Luminous flux is a unit of measurement used to quantify the amount of visible light emitted by a light source. It indicates how much light the lamp generates and is an important factor in choosing lighting for a particular space or application.
Unlike luminous intensity (measured in candelas ), which measures the amount of light in a specific direction, luminous flux indicates the total amount of light emitted by a light source. A lamp with high luminous flux produces a lot of light, while a lamp with low luminous flux produces less light.
Units of luminous flux
The unit of luminous flux is lumen (lm) . This is the amount of light emitted in all directions by a light source. It is a measure of the lamp's overall brightness .
- 1 lumen (lm) is the luminous flux generated by a light source of 1 candela (light intensity) in a space of 1 steradian .
For example:
- A 60-watt incandescent bulb produces approximately 800 lumens .
- A 10-watt LED bulb can produce the same amount of light, which is much more energy efficient than the incandescent bulb.
How luminous flux is used
Luminous flux is particularly important for determining the brightness of a light source, which affects how well a room is illuminated. The amount of lumens required for a room depends on several factors, such as the room's size, the color of the walls and ceiling, and the desired brightness.
Example:
- Bedroom (approx. 10-15 m²) : About 1500-2500 lumens is often sufficient for general lighting.
- Kitchen (approx. 10-15 m²) : Approximately 3000-4000 lumens , as work areas in the kitchen often require more light.
- Living room (approx. 20 m²) : Approximately 3000-5000 lumens , depending on the desired atmosphere and activity.
Luminous flux and types of lighting
- Incandescent bulbs : Traditional incandescent bulbs produce relatively little luminous flux compared to modern energy-efficient light sources. For example, a 60W incandescent bulb produces about 800 lumens.
- Halogen lamps : Halogen lamps are a type of gas discharge lamp that produce more light than a standard incandescent bulb for the same wattage. A 50W halogen lamp can deliver approximately 900-1000 lumens.
- Fluorescent Lamps : Fluorescent lamps, such as fluorescent tubes, typically produce more luminous flux than incandescent and halogen bulbs while consuming less energy.
- LED bulbs : LED bulbs are highly energy-efficient and offer high luminous flux per watt. A 10W LED bulb can easily produce 800 lumens or more, equivalent to the light output of a traditional 60W incandescent bulb.
Luminous flux and efficiency
The efficiency of a light source is often expressed as lumens per watt (lm/W) . This indicates how much light a lamp produces relative to its energy consumption. LEDs, for example, have a much higher lumen output per watt than incandescent or halogen bulbs.
Example of lumens per watt:
- Incandescent lamp : About 10-15 lm/W .
- Halogen lamp : About 15-20 lm/W .
- Fluorescence : About 35-100 lm/W .
- LED : About 80-100+ lm/W .
This means that LED lights use much less energy to produce the same amount of light as older technologies, making them much more energy efficient.
Luminous flux and color temperature
The color temperature of a light source, measured in Kelvin (K) , doesn't directly affect luminous flux, but it can influence how we perceive light intensity. For example, with warm white lighting (around 2700K ), the light will be perceived as softer and less harsh than with cooler white lighting (around 5000K ), even if the luminous flux is the same.
Summary
Luminous flux (lumen) is the measure of the amount of light a light source emits in all directions . It represents the overall brightness of a light source and is an important metric when choosing lighting for a space. The more lumens a lamp produces, the brighter the light will be. Luminous flux is crucial in choosing the right lighting for various applications, such as homes, workspaces, and commercial settings, to achieve the desired brightness and ambiance.