When choosing a lighting fixture, understanding brightness measurements is essential. In today's market, three key metrics help describe brightness: candela, lux, and lumens. In this guide, we’ll break down the differences between lumens, lux, and candela, explaining each unit and how they relate to each other.
Lumen is a unit that measures how much visible light a light source gives off. It describes the total amount of light emitted, regardless of direction.
Factors influencing lumen value:
● Light source type: Different lighting technologies have different luminous efficacies, resulting in different lumen outputs at the same wattage.
● Power: Among the same type of light sources, power is an important factor affecting the lumen value.
● Lumen depreciation: During the use of a light source, the value of lumen will gradually decrease over time.
To work out lumens with a lux meter, remember that lux measures how much light hits an area, and lumens are lux multiplied by that area. First, use the lux meter to check the light level and write down the reading. Then, measure the size of the surface the light is shining on in square meters. Multiply the lux reading by this area to get the lumens. For example, if your meter shows 500 lux and the light covers 3 m², you have 500 × 3 = 1500 lumens.
This works best if the light spreads evenly; if not, or if you want the bulb’s total output, you’ll need more measurements or special tools. Keep in mind that how far you are from the light will change the reading.
Candela is a unit of luminous intensity in a particular direction. It is sometimes expressed as ‘candlepower,’ abbreviated as cd. It doesn’t measure the total amount of light but instead shows how focused the light is in a certain direction. Candela is a key standard when directional or task lighting are important, such as in spotlights, flashlights, or automotive headlights.
Factors impacting candela value:
● Beam angle: Narrower beams concentrate light into a smaller area, resulting in higher candela values.
● Reflective devices design: The ability of reflective devices such as reflectors and mirrors to converge light directly affects the candela value.
● Focusing effect of the lens: A lens can adjust the focus or divergence of light through refraction.
Candlepower is an older term for candela. Historically, it was based on the light intensity produced by a standard candle, but modern lighting standards use candela (cd) as the official SI unit.
Any light eventually becomes too dim to see when you're far enough away from it. That means the CD rating is different from lumens because you're looking at an intensity rating vs. a total light output measurement. Products like spotlights and laser pointers tend to have high candela ratings because most of the illumination focuses in a single direction.
You can calculate it if you know the luminous flux and the solid angle over which the light is emitted. The formula is candela = lumens ÷ steradians. To do this, first measure or estimate the total lumens of the light source, then find the solid angle it covers, which depends on how wide the beam spreads. For example, a light emitting 100 lumens evenly over 1 steradian has an intensity of 100 candela. This method assumes the light is evenly distributed within the measured angle; for real-world lights, beam patterns may require more detailed measurements. Most manufacturers obtain candela values through photometric testing.
One lux (lx) is defined as one lumen of luminous flux distributed over one square meter of surface area. This unit helps determine the intensity of light reaching a given space, making it useful for assessing lighting conditions in a room or outdoor area.
Factors to lux value:
● Distance from the light source: Illuminance decreases as the distance between the light source and the illuminated surface increases.
● Mounting height: Fixtures installed at greater heights distribute light over a larger area, which generally lowers the lux level on the working surface.
● Surface reflectance: Light-colored walls, ceilings, and floors reflect more light, helping increase overall illuminance.
Because illuminance changes with distance, lux values are often specified together with a measurement distance, especially for spotlights, flashlights, and directional lighting products. Lux decreases with distance, so the same fixture can produce different illuminance levels depending on the mounting height. For example, if a 500-lumen spotlight illuminates one square meter, the surface receives 500 lux. Now let's say the spotlight gets backed up so that it now shines over five square meters. Even though the lumens stay the same (500), the lux rating decreases to 100 because of the extra space that requires illumination.
What does lux look like in real life? To put it in context, 1 lux is roughly equivalent to moonlight. Typical office lighting ranges from 300 to 500 lux, depending on local standards and task requirements. A dim, overcast day might measure about 100 lux, while full daylight reaches 10,000 to 25,000 lux. On a bright, sunny day, direct sunlight can soar up to around 100,000 lux.
The basic way to calculate lux is by dividing the total luminous flux incident on a surface by the area of that surface, using the formula: Lux (lx) = Luminous Flux (lm) / Area (m²).
Practical factors like the angle of incidence matter too. If light hits a surface at an angle, illuminance is reduced by the cosine of that angle, meaning light at 60° would cut illuminance in half. It’s important to note that non-uniform sources, such as spotlights, don’t follow the inverse square law as cleanly as uniform point sources.
Lumens indicate the total light output of a fixture, while candela focuses on the intensity of light in a specific direction. This is the main difference that often leads to confusion between the two units.
The relationship between lumens and candela depends on the beam angle and light distribution. Since candela and lumens measure different aspects of light, comparing them directly is not meaningful — always compare products using the same unit. Comparing lumens to candela directly is not meaningful; you should compare products using the same unit. It’s advised to compare two candela or two lumens ratings.
Candela ratings remain unchanged when part of the light is obscured, but lumen ratings decrease because less total light is emitted.
For example, a light bulb rated at 3 cd. That product would provide approximately 38 lumens when it offers uninterrupted illumination. Let's say that half of the bulb gets obscured, leaving a single hemisphere to provide illumination. The 3 CD rating remains unchanged because the parts left unobscured are still visible from the same distance. But if you measured the lumens in that situation, it would cut the rating by 50%. That's because you're only looking at the visible light from the source.
A lower-lumen flashlight can sometimes appear brighter than a higher-lumen model if its beam is more focused.
While lumens measure total light output, a narrower beam concentrates that light, increasing candela (intensity) and resulting in higher illuminance (lux) on the target surface. By contrast, a high-lumen flashlight with a wide beam spreads light over a larger area, so the light at any single point is lower.
That’s why a 1,000-lumen spotlight can appear brighter on a distant object than a 2,000-lumen floodlight.
Here is a flashlight data table to help you understand the relationship between lumen, candela and beam distance.
| Luminous Flux (Lumens, lm) | Light Intensity (Candela, cd) | Beam Distance (m) |
|---|---|---|
| 5000 | 87719 (Narrow beam) | 592 |
| 5924 (Wide beam) | 154 | |
| 1500 | 26316 (Narrow beam) | 324 |
| 1777 (Wide beam) | 84 | |
| 700 | 12281 (Narrow beam) | 222 |
| 829 (Wide beam) | 57.6 |
The main difference between lux and lumens is what they measure: lux measures how much light lands on a specific surface, which indicates how well-lit a particular area will be. Lumens measure the total light output from a source. For instance, when a high-lumen light source is placed far away, it won't provide much lux on a surface, but when it is close by, the lux increases because more light is concentrated on that spot. Therefore, lux can tell how well a specific space will be illuminated.
Every light contributes to the candela, lux, and lumens ratings achievable in that space. From accent to task lighting, you'll want to consider each specific need to understand what to install or use as a replacement.
Here's an easy way to remember the different ratings so that you get the correct bulbs for your space.
● Candela measures the levels of visible light intensity from the source.
● Lux describes how bright surfaces are once the bulbs are correctly installed.
● Lumens measure how much total light a source emits.
Once you know those descriptions, finding an appropriate replacement solution is much easier.
In the business field, enterprises need to select products based on different applications. Here are some real-world commercial examples to learn which one you should pay more attention to.
Pay Attention to Lumens
● Office: Reducing eye fatigue and minimizing distraction caused by overly dim or bright light in working areas.
● Retail store: Uniform basic lighting ensures that customers can clearly observe the details of the products in the retail store.
● Healthcare facilities: General lighting in hospital corridors and waiting areas should avoid excessive contrast between light and dark to prevent patients from falling.
● Data center: Adjusting the angle and candela to precisely illuminate the area lighting, cable interface or label on the top of the cabinet.
● Stage: Follow spots must deliver sufficient candela to maintain precise focus on performers across varying stage distances.
● Art galleries: Adjusting the light intensity according to the type of exhibits to make sure that the audience can observe clearly.
● Restaurants: Illuminating the dining table with narrow-beam lighting to enhance the visual appeal of the dishes.
● Warehouse: In warehouses, lux levels affect visibility, safety, and operational efficiency.
● Schools and educational facilities: Classrooms, laboratories, and libraries require specific lux levels to support reading, writing, and learning activities.
● Sports area: Stadium standards are almost always specified in lux because player visibility, safety, and broadcasting quality depend on the illuminance on the playing surface.
Understanding the relationship between lumen, candela, and lux is essential for effective lighting design. It helps you interpret product specifications correctly and avoid selecting fixtures based on lumen alone. By considering light distribution, installation height, and illuminance together, you can choose the right fixtures, optimize lighting layouts, and achieve the desired brightness and visual comfort. For project-specific lighting recommendations, contact LEDVANCE for photometric support and fixture selection guidance.
One candela equals one lumen per steradian (lm/sr), meaning it measures luminous intensity within a specific directional cone. To convert candela to lumens, multiply by the solid angle in steradians the light covers for a full sphere (4π steradians), 1 candela emits about 12.57 lumens. However, since candles are directional and lumens are total output, direct conversion depends on the beam's spread.
10,000 candelas are roughly as bright as a modern car headlight on high beam or a powerful spotlight. At close range, it can appear blinding, similar to staring at a bright LED flashlight at full power. The perceived brightness also depends on distance, beam angle, and ambient lighting conditions.
No, 5000 lux and 5000 lumens are completely not the same concept. 5000 lumens is merely the total output of light, while 5000 lux represents the actual illumination brightness. The relationship between the two depends on the size of the irradiated area. For instance, with the same 5000 lumens, if the light is concentrated on 1 square meter, it equals 5000 lux. But if it is distributed over a 10-square-meter area, it is only 500 lux.
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