Flashlight Knowledge

Candela vs Lumen

Jun 26, 2023

Wuben X3
When it comes to understanding the metrics used to measure light, two terms often come up: candela and lumen. These units of measurement play a crucial role in the field of lighting design and technology, as they relate to the amount of light emitted. However, there are important distinctions between the two. Here, we will delve into the depths of candela and lumen, exploring their definitions, applications, and how they differ from each other.


Candela is a fundamental unit of measurement in the International System of Units (SI), used to quantify the intensity of light emitted from a source in a particular direction. It is defined as the luminous intensity of a light source that emits monochromatic radiation with a frequency of 540 terahertz (THz) and an intensity of 1/683 watt per steradian. In simpler terms, candela measures the brightness of a light source in a specific direction.

In lighting design, candela plays a significant role in determining the required intensity of light for various applications. For example, architects use candela to assess the illumination levels needed in specific areas to ensure safety and visual comfort. By understanding the measurement of candela, lighting professionals can strategically position light sources to achieve desired effects and meet lighting standards.


On the other hand, lumen measures the total quantity of light emitted by a source, regardless of the direction in which it is emitted. It is a unit of measurement used to quantify the brightness of light as perceived by the human eye. Unlike candela, which focuses on the intensity of light in a specific direction, lumen provides a holistic measure of the total luminous flux emitted by a light source.

Lumen is particularly important in lighting technology, as it helps determine the overall brightness of a light fixture or lamp. By measuring the luminous flux in lumens, manufacturers can provide accurate information to consumers about the brightness of their products. This enables individuals to select the appropriate lighting solutions for their needs, whether it's creating an ambient atmosphere or illuminating a workspace.

Candela vs Lumen

Now that we have a clear understanding of candela and lumen, let's explore the key differences between these two metrics.

Firstly, the focus of measurement differs. Candela primarily concerns the intensity of light emitted in a specific direction, taking into account factors such as the angle and distance from the light source. On the other hand, lumen provides a measure of the overall brightness emitted by a source, regardless of the direction.

Secondly, there are perceptual differences based on the sensitivity of the human eye. The eye's response to light is not uniform across the entire spectrum of visible light. Our eyes are more sensitive to certain wavelengths, particularly those in the green-yellow region. Candela accounts for this sensitivity by using a reference frequency of 540 THz, which aligns with the peak sensitivity of the human eye. Lumen, being a holistic measure, incorporates the eye's sensitivity curve to provide an accurate representation of brightness as perceived by humans.

Lastly, the practical applications of candela and lumen differ. Understanding the required intensity becomes crucial when choosing lighting fixtures for specific tasks or environments. For example, in accent lighting, where directional light is desired to highlight specific objects or architectural features, candela is a more relevant metric. Conversely, when selecting general lighting solutions for a room or space, lumen serves as a practical measurement for determining the overall brightness needed.

In conclusion, candela and lumen are two distinct units of measurement used in the realm of lighting. While candela focuses on the intensity of light emitted in a particular direction, lumen provides a holistic measure of the total luminous flux emitted by a light source. Understanding the differences between these metrics is essential for lighting professionals, architects, and consumers alike. By grasping the nuances of candela and lumen, one can make informed decisions about lighting design and select appropriate lighting solutions for specific applications. So, whether you're an architect seeking optimal illumination levels or a homeowner looking to create the perfect ambiance, delving into the depths of candela and lumen will undoubtedly shed light on your path to lighting excellence.

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