Candela, Lux and Lumens are the most common units of light in daily life, are you often confused by the three, it’s okay, this article will let you know their relationship, calculation and application scenarios from shallow to deep. Let’s take a look below.
What is Candela?
Candela is mainly a unit used to measure the intensity of light. It is derived from the Latin word “candela”, which means “candle light”. The name may be unfamiliar to the general public, but it is not so different from other units of measurement.
It was created to give a precise measure of the intensity of light. It’s like when we say that this person and that person are both “taller”, but we don’t have a precise description of who is taller and who is lower.
Similarly, when we say that the light is “brighter”, how bright is it? Until there is a unit of luminous intensity, the candela, we cannot describe it precisely. Therefore, this is the main reason why the candela was defined.
What is Lux?
“Lux” sounds like a person’s name. In fact, it is not a specific person’s name, nor is it named after the person who defined it. Like candela, it is derived from Latin. Lux means “light” in Latin, and its main purpose is to quantify the intensity of light.
What is Lumens?
We often see lumens labeling on LED bulbs or types of products. Lumens are a measure of the total amount of visible light emitted by a light source. Simply put, the higher the lumen number, the brighter the bulb.
In many indoor scenes, we need to comprehensively calculate the lumens of each light-emitting object in order to be able to match the most reasonable lighting scheme.
What are the relationships between Candela, Lux, and Lumens?
Candela, Lux, and Lumens are all units of measurement of light, and as such they can be interchanged under certain conditions. Candela is a measure of the intensity of light, Lumens is a measure of the output of light, and Lux is a measure of the area of an object illuminated by light. Let’s use a practical example to explain the relationship between them.
Suppose we light a candle in a completely dark house. If this candle is a source of light, then the light emitted by this candle in a certain direction can be expressed in terms of Candelas; the same candle, which generally does not emit light in only one direction, but in all directions, so the sum of the light emitted by this candle in all directions is Lumens; the light emitted by this candle can ultimately illuminate an area is Lux.
How to calculate Candela, Lux, and Lumens?
These units of light are defined so that light can be visualized for everyday use. Next, let’s look at how these three units of light are calculated.
Calculation of Candela
1 candela is equal to 1/683 watts per spherical degree (sr) the luminous intensity of monochromatic radiation with a frequency of 540×10¹²Hz, which can be expressed by the formula:
1 cd = lm/sr
Calculation of lumens
Candela and lumens can be converted to each other, so we can deduce the formula for lumens from the above equation:
1 lm = 1 cd-sr
Calculation of lux
Since lux is an indication of the intensity of lumens uniformly distributed over an area of 1 square meter, the formula for lux can be expressed as:
1 lx = 1 lm/m²
Candela, Lux, and Lumens Interconversion Equation
From the above three formulas, we can further derive the Candela, Lux, and Lumens interconversion formulas:
1 lx = 1 lm/m² = 1 cd-sr/m²
Application scenarios for Candela, Lux, and Lumens
Although they can be converted to each other, their definitions are not the same, so there are some differences in their application scenarios, so let’s take a look at each of them.
Application Scenarios of Candela
Lighting engineering basic research
When studying the luminous properties of a light source, we are better able to obtain the desired effect. For example, when we test a variety of different light bulbs in the lab, determining their luminous intensity helps to design a softer bulb, which plays an important role in reducing light pollution.
Optical Instrument Calibration
For various precision optical instruments, such as microscopes, telescopes and other devices, the luminous intensity must be adjusted with extreme precision. These instruments are calibrated in candelas when the light source is adjusted. Different luminous intensities will ultimately affect the morphology of the organisms under the microscope and therefore need to be calibrated very finely.
Stage Lighting Design
Different types of lighting fixtures (e.g., spotlights, floodlights, catch lights, etc.) have different luminous intensities, and how to adjust these lights to achieve the desired effect is measured in candelas.
When we calculate the light intensity of different areas of the stage, we can target the adjustments to achieve the desired effect. A more common example is when we need to highlight the protagonist, we will dim the other lights, and then the high luminous intensity of the spotlight on the protagonist.
Application Scenarios for Lumens
Luminaire Lighting Performance Evaluation
In the past, when we purchased a luminaire, we needed to consider not only which wattage was higher, but also which material was used to be more energy efficient. But the fact is that wattage is not always proportional to the brightness of a luminaire.
When the wattage of the bulb exceeds 50 watts, as the wattage continues to increase, the brightness will not continue to increase, but will remain the same, or even decline, and secondly, different materials will also affect the lumen value of the change, for example, the same to produce 1,000 ml, the use of white weave lamps need to be 100 watts, while the LED lamps only need 12 watts. It is for these reasons that the way of judging the brightness of a luminaire by its wattage is out of history.
When we use lumens as a judgement for lamps, we can choose the right brightness by the lumen value without having to consider too many other factors (wattage, material, current, etc.) affecting our purchase.
Interior Lighting Design
Interior designers need to arrange the total luminous flux (total lumen value) according to the size of the room and the ambience requirements when planning the lighting program. Generally speaking, a 20 square meter living room requires about 2000–3000 lumens of total luminous flux.
A bedroom of the same 20 square meters, on the other hand, usually requires only 1000–1500 lumens. If you don’t calculate this piece, then it can lead to too much light in certain areas, which can affect the lighting situation of the entire space.
Automotive Lighting System Design
Car manufacturers likewise need to consider different lumen values when designing the various lights in a car. The purpose of this is to ensure that the road is illuminated, but also to avoid disrupting the passage of other vehicles because of too much light. Most of the current electric vehicles have headlights with a luminous flux of 5000 lumens. And the reading light inside the car is usually designed as 200–300 lumens.
Application Scenarios of Lux
Architectural Lighting Standard Measurement
Lux is an important unit in the construction industry to measure whether the lighting of indoor and outdoor environments meets the standard. For example, in order to meet the daily needs of the office, the illuminance standard of the office will generally be designed between 300-500 lux, while the school classroom in order to ensure that the students can see the content of the blackboard, it will be designed between 300-750 lux.
Lighting Design for Industrial Environments
Similar to the office lighting design environment, there are industrial production workshops. Different production workshops have different requirements for illumination.
Generally speaking, in the assembly of precision electronic components in the workshop, the need for high illumination of 1000-1500 lux, in order to ensure that workers in the assembly can clearly see the position.
In addition, the design of high illumination can also make the workers’ eyes not easy to fatigue, to produce greater labor efficiency, which is very helpful when the workers on the night shift. And the same workshop, if the storage area, usually only need 100-300 lux is enough.
Photography, virtual shooting and film production
In the field of photography, virtual production, lux is used to measure the light intensity of the scene being filmed. Photographers and videographers need to control the illumination level according to the subject and the effect required.
For example, when shooting portraits, the right level of illumination (e.g., 500–1000 lux) can make the character’s face evenly lit and skin color natural; when shooting landscapes, depending on the weather and time of day, the illumination level may vary greatly, and the photographer can adjust the exposure parameters by measuring the lux value.
Conclusion
This article provides a detailed introduction to Candela, Lumens and Lux, and I believe that by reading this article, you have a deeper understanding of Candela, Lumens and Lux.
