Lightbulbs in a rowWhen it comes to lighting, we often come across terms like candela and lumen, which are used to measure different aspects of light. While both metrics are essential in assessing the performance of lighting systems, they represent distinct characteristics of light. In this blog, we will delve into the differences between candela and lumen, exploring their definitions, applications, and how they contribute to our understanding of lighting efficiency.

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Candela - A Measure of Luminous Intensity:

Candela (cd) is a metric used to quantify the luminous intensity of a light source. It specifically measures the amount of light emitted in a particular direction by a source. Candela provides information on how bright a light source appears to the human eye. The term "candela" originates from the Latin word for "candle" and was historically used to describe the brightness of a standard candle.

The candela measurement is important for various applications, including lighting design, architectural lighting, outdoor lighting, and industrial settings where visibility and task performance are crucial. It helps designers determine the appropriate lighting levels required for specific areas or tasks, ensuring adequate illumination. For example, in a museum setting, the use of high-candela spotlights can highlight specific artworks, creating a focal point for viewers.

Lumen - A Measure of Luminous Flux:

Lumen (lm) is a metric used to quantify the total amount of visible light emitted by a light source in all directions. It measures the luminous flux or the total amount of light output from a source, irrespective of the direction in which it is emitted. In simpler terms, lumen indicates the brightness of a light source as perceived by the human eye, regardless of where the light is directed.

Lumen is a fundamental metric for evaluating the overall light output of a lighting fixture or system. It is particularly useful when comparing different light sources or bulbs to determine their efficiency and suitability for various applications. By considering the lumen output, consumers can make informed decisions regarding the brightness levels required for different spaces, such as homes, offices, or commercial settings. Additionally, lumen measurements play a vital role in energy efficiency assessments, helping users select lighting options that provide optimal light output while minimizing energy consumption.

Learn the difference between initial lumens and mean lumens

Relationship between Candela and Lumen:

While candela and lumen both relate to light, it is essential to understand that they measure different aspects of lighting. Candela measures the intensity of light in a specific direction, whereas lumen measures the total light output regardless of direction. In simpler terms, candela tells us how bright a light source appears from a specific angle, while lumen informs us about the total brightness emitted by the source.

To further understand their relationship, it is necessary to mention the concept of solid angle. Solid angle is a measure of the amount of three-dimensional space an object subtends at a specific point. Candela is a measure of luminous intensity per unit solid angle, while lumen is a measure of luminous flux that takes into account the entire solid angle.

To put it in perspective, imagine a spotlight that emits 1,000 lumens. If this light source has a focused beam that concentrates its output in a narrow direction, it may have a high candela rating. In contrast, if the same 1,000 lumens are emitted uniformly in all directions, the candela rating would be lower since the light is dispersed over a larger solid angle.

The relationship between candela and lumen is further illustrated by the concept of luminous efficacy, which measures how effectively a light source converts electrical power into visible light. Luminous efficacy is expressed in lumens per watt (lm/W). By considering both candela and lumen measurements alongside luminous efficacy, we can gain a comprehensive understanding of a light source's performance in terms of both brightness and energy efficiency.

For instance, LED (light-emitting diode) technology has revolutionized the lighting industry with its high luminous efficacy. LEDs can produce a significant amount of lumens while consuming relatively less energy compared to traditional incandescent bulbs. This means that LEDs can provide the same or even higher levels of brightness (lumens) while using fewer watts of electricity.

Understanding the relationship between candela, lumen, and luminous efficacy is crucial when designing lighting systems that need to meet specific requirements. By considering the desired brightness levels (lumens) and the directionality of light (candela), lighting professionals can select the appropriate light sources, fixtures, and placement to achieve the desired lighting effects. They can ensure that the light is focused where it is needed, minimizing wasted light and maximizing efficiency.


Candela and lumen are vital metrics in the world of lighting, each providing valuable information about different aspects of light. While candela measures the luminous intensity in a specific direction, lumen measures the total light output regardless of direction. Understanding the distinction between these metrics is essential for selecting appropriate lighting solutions for various applications, considering both brightness and energy efficiency. By considering candela, lumen, and other relevant metrics, individuals can make informed decisions to achieve optimal lighting conditions that enhance visual comfort, productivity, and aesthetic appeal in their surroundings.

As lighting technology continues to advance, it is crucial to stay updated on the latest developments and trends in the industry. With a solid understanding of lighting metrics, individuals can make informed choices when it comes to selecting lighting products, designing lighting layouts, and creating environments that are visually pleasing, energy-efficient, and conducive to the well-being of occupants.

To learn more about candela and lumen applications, visit Shine Retrofits’ website or contact us today!