Nov 05.2022

Candela vs. Lux vs. Lumens: The Relationships and How to Calculate?

What is Candela?


What is Lux?

What is Lumens?

What are the relationships between Candela, Lux, and Lumens?

How to calculate Candela, Lux, and Lumens?


What is Candela?


Light intensity measured in candelas. A candela is the amount of light emitted in one steradian from a source with a monochromatic radiation spectrum centred at 540 1012 Hz and a radiant intensity of 1/683 watt. This measurement standard conforms to the ISO's rigorous standards (SI).


The candela has been used in several disciplines, from astronomy and photography to the measurement of light transmission via optical fiber. The quantity of light from a particular source may be readily determined by measuring its luminous intensity.


The candela is a widely used unit of measurement for light because of its versatility. The astronomical community is a significant user of the candela unit. The candela is the unit of measure used by astronomers to determine the total amount of light coming from a star. Given that a star's luminous intensity may be pretty great, and because the candela unit allows for precise measurement, this makes sense.


It's common practice for photographers to utilize the candela unit. Photographers use the candela unit to determine how much light is required to get the desired exposure. This is because the candela unit permits precise measurement of the luminous intensity of a light source, which can change.


The light output of optical fiber cables may also be measured using the candela unit. Engineers use the candela unit to determine the quantity of light transmitted via an optical fiber. That's because the candela unit provides a precise reading of the light intensity emitted by a visual fiber line, which can be relatively high.


What is Lux?


A lux is a unit of illuminance and luminous emittance based on the international system of units (SI). In other words, it's the same as one lumen per square meter. This unit of measurement is used to quantify the amount of light striking a particular area.


Lumens quantify the entire quantity of light emitted by a source or the luminous flux. The amount of light that illuminates a surface is measured in units called lux. Luminous flux is a measure of the overall quantity of light, whereas illuminance is a measure of how much light hits a surface.


The illuminance required for a specific work may be quantified using the lux scale. The illuminance in an office may be set at 500 lux, whereas in a factory, it might be set at 1000 lux. More illumination is needed when the lux value rises.


Human health and happiness both benefit from enough exposure to lux. Exposure to light at night may mess with our sleep cycles, and when it's too bright during the day, it can strain our eyes. A proper quantity of light may be guaranteed by measuring it in lux.


Illuminance and luminous emittance are measured in lux, the SI-derived unit for light flux per unit area. It's a vital resource for determining how much illumination is needed to accomplish a particular work, which may aid in preserving our health and well-being.


What is Lumens?


The quantity of light produced by an object is expressed in lumens, the SI unit of luminous flux. The light emitted by a candle at a solid angle of one steradian equals one lumen. The visible range of a light source is directly related to its brightness, which is often measured in lumens.


Middle-range visible light is where the human eye is at its most sensitive, and lumens are the standard unit of measurement for how bright a light is. In 1884, German scientist Wilhelm Eduard Weber established the lumen as a standard measure for light intensity.


As of 1930, it has been a recognized SI unit. The lumen is presently the standard against which the candela, the unit of light intensity, is measured. The power of a point source of monochromatic light with a 555 nm wavelength and a luminous flux of 1 cd/m2 equals one candela.


What are the relationships between Candela, Lux, and Lumens?


Candela (cd), Lux (lx), and Lumens are the three main ways that light may be measured (lm). The lumen measures the average brightness over a larger area than the candela, which is why the two units are often confused. However, the quantity of light emitted by a source may be quantified using lumens. Candela, Lux, and Lumen's connections are grounded like light itself.


Light intensity is measured in candelas, while light output is measured in lumens. How bright something is measured in lux. There is no way to choose the optimal illumination without all three components. One may think of the Candela, the Lux, and the Lumen as one unit of light intensity, with 1 Candela equaling 1 Lux and 1 Lumen.


As a result, they are all measuring the same thing but in different ways. Because it measures light intensity in a single direction, the candela is the most exact unit of measurement. Light intensity is measured in lux, which is not quite as precise. One of the least accurate metrics is the lumen, which accounts for how much light is produced. The answer to your query is that the Candela, the Lux, and the Lumen are all measuring the same, although in different ways.


The lumen is the less accurate unit of measurement compared to the candela. We may choose the most appropriate lighting for any circumstance by understanding the links between Candela, Lux, and Lumens. To determine the candela's lumens and lux, we need to know the candela's value. Having access to this data is crucial when deciding on a lighting fixture.


How to calculate Candela, Lux, and Lumens?


Calculating Candela


There is a connection between the candela, the lumen, and the lux. The total amount of light produced by a source is measured in lumens. The total luminous flux of a light beam is 1 lumen when its intensity is 1 candela, and its space angle is 1 steradian (which for a cone-shaped beam is equal to an opening angle of 65.5 �). Therefore, 1 lumen per steradian is equivalent to 1 candela. Illuminance is measured in lux and is similar to the number of candlepower required to illuminate a one square meter area with a beam of strength one lumen. That's why 1 lux is equivalent to 1 lumen per square meter.


Calculating Lux


Luminance is measured in lux (sign lx), which comes from the Latin word for light. One lux is equal to the amount of light produced by one candela at a distance of one meter on a surface perpendicular to the light beams.


Therefore, the lux equals the amount of light emanating from a one-lumen light source and falling on one square meter of the surface under test. Therefore, 1 lux = 1 lumen / m2 is the formula for determining the amount of light that illuminates a specific area in square meters.


Different distances may be used to measure lux. Take care when making a direct comparison between two lights. Light measured in lumens at one meter is much weaker than estimated at three meters.


Any surface or area may have its lux level measured using a light meter. Make sure the light meter is at a convenient height for you while taking readings. As the distance between the light and its target increases, the illumination level in the square decreases.


Calculating Lumen


It is a way to quantify the overall brightness of a light source. The visible portion of electromagnetic radiation is taken into consideration in the calculation of luminous flux. The brilliance of a light source may be measured in terms of lumens regardless of the direction in which the light is being emitted.


The quantity of light produced by a light source is quantified by its luminous flux. The density of a given light source is quantified by its intensity. A lesser luminous flux (in lumens) but theoretically the same luminous intensity (in candelas) is emitted by the portion of the light beam that is visible.


The intensity of the light and the color of the morning both affect the luminous flux. About 12 lumens per watt is the average luminous flux from a standard incandescent bulb. The brightness of an emitted light source increases with decreasing radiation angle (with constant luminous flux).


One helpful method to recall the many distinctions is as follows:


  • * The amount of light emitted is measured in lumens.
  • * A surface's luminous flux, measured in lux, is the measure of its brightness.
  • * The visual intensity of a light source is quantified in terms of candela.




The minimum illuminance required for various locations, tasks, and gadgets is laid out in lux in the illumination standard NEN-EN 12464-1. The standard establishes guidelines for adequate illumination in indoor workplaces from visual comfort and productivity perspectives-the standard accounts for all typical visual activities, including screen-based work.


Intensifying the amount of light that can be seen is necessary if:


  • * There must be a focus on the eyes;
  • * Mistake correction takes too much time or money;
  • * precision or high output must be prioritized;
  • * There are just a few distinguishing features, or the contrast is muted;
  • * Abnormally large amounts of time are spent on this activity;
  • * This worker has a less-than-ideal vision.


A decrease in the use of illumination is required if:


  • * Very big or high-contrast details;
  • * The time required to complete the work is concise.




Candela, Lux, and Lumen all have complicated relationships. The Candela is the standard unit for measuring light intensity, whereas the Lux is the standard unit for measuring total visible light. However, the quantity of light that reaches a given area is quantified in lumens. Understanding the distinction between these metrics is a prerequisite before calculating them.