Lumen is the standard unit of measurement for luminous flux in the International System of Units (SI). Luminous flux refers to the total amount of visible light emitted by a light source per unit of time. In simpler terms, it measures the total brightness of a light source, encompassing all the light emitted in all directions.
Another way to understand luminous flux is as the “flow” of light, similar to how we might measure the flow of water in liters per second. The more lumens a light source emits, the brighter it appears to an observer. Therefore, when you see a lumen rating on a light bulb or a lighting fixture, it indicates how much light that particular source emits, allowing you to gauge its brightness relative to other light sources.
Lumen Easy Explanation:
Here is detailed explanation of the relationship between luminous intensity, apex angle, and total luminous flux. This relationship is crucial to understand when selecting lighting solutions, especially when considering factors like brightness and beam angle.
In summary, the luminous intensity of a light source, measured in candela (cd), is directly related to the angle over which the light is emitted. LEDs with a high luminous intensity typically have a narrow apex angle, resulting in a concentrated beam of light and higher intensity in that direction. Conversely, LEDs with a wider apex angle emit light over a broader area, resulting in lower luminous intensity.
Total luminous flux, measured in lumens (lm), takes into account both the luminous intensity and the angular span over which the light is emitted. The relationship between luminous intensity (Iv), angular span (Ω), and total luminous flux (Φv) is given by the formula Φv = Iv ⋅ Ω.
For isotropic light sources that emit light uniformly in all directions, the total luminous flux is calculated by multiplying the luminous intensity by 4π steradians (the total solid angle of a sphere). This relationship is expressed as
Φv = 4π Iv.
As a point of reference, a standard 230V/60W incandescent light bulb typically produces around 700 lumens of total luminous flux, while a low-voltage (12V) tungsten halogen lamp rated at 20W yields approximately 310 lumens.
Understanding these relationships allows for informed decisions when choosing light sources for various applications, considering factors such as desired brightness, beam angle, and energy efficiency.
Following picture shows the difference among lumen, candela and lux.
What is a lumen?
A lumen is a unit of measurement used to quantify the total amount of visible light emitted by a light source in all directions. It measures the brightness of a light source as perceived by the human eye.
How is the lumen defined?
The lumen is defined as the amount of light emitted by a light source that falls on a one-square-foot area located one foot away from the source. It represents the total luminous flux emitted by the source.
Why is understanding lumens important?
Understanding lumens is important for selecting the right lighting products, such as light bulbs or LED fixtures, to meet the desired brightness level for a specific space or application.
How are lumens different from watts?
Watts measure the electrical power consumed by a light source, while lumens measure the total light output emitted by the source. Lumens provide a more accurate indication of brightness, whereas watts are a measure of energy consumption.
Do higher lumens mean brighter light?
Yes, higher lumens generally indicate a brighter light output. The more lumens a light source emits, the brighter it appears to an observer.
How are lumens measured or calculated?
Lumens are measured using specialized equipment that quantifies the total amount of visible light emitted by a light source in all directions. The measurement takes into account the spectral sensitivity of the human eye.
What is the relationship between lumens and other lighting terms like lux and candela?
Lumens measure total light output, while lux measures light intensity on a surface (lumens per square meter), and candela measures luminous intensity in a specific direction.
Are lumens the same as brightness?
Lumens are a measure of brightness, but they do not necessarily account for how the light is distributed or perceived. Factors like beam angle and color temperature also affect perceived brightness.
How many lumens do I need for different applications?
The number of lumens needed depends on factors such as the size of the space, the intended use, and personal preference. For example, task lighting may require higher lumens for adequate visibility compared to ambient lighting.
Can lumens be compared across different types of light sources?
Yes, lumens provide a standardized way to compare the brightness of different types of light sources, regardless of their technology or design. This allows consumers to make informed decisions when selecting lighting products.