Candela vs Lux vs Lumens
Light is an essential element in our lives and is measured in a variety of units. And each unit has a specific purpose. If we want to understand light, we must first understand these three units. Candela, lux and lumen are the three basic units used to quantify different aspects of light. Although they sound similar, they represent different characteristics of light, and understanding the differences between candela vs lux vs lumens is essential to making informed decisions about lighting solutions.
What Is Candela?
The candela (cd) is the international unit of luminous intensity that quantifies the brightness of a light source in a specific direction. This measurement helps determine how concentrated a light source’s output is within a specific angle, which is critical for applications that require focused lighting.
Unlike other lighting metrics, the candela does not measure the total amount of light emitted, but rather its directional intensity.
Key Characteristics
- Directional Measurement: The candela assesses the intensity of light within a specific solid angle (stereoscopic angle). This is critical for applications where directionality is important, such as headlamps or spotlights.
- Defined Standard: The value of one candela is approximately equal to the luminous intensity produced by a single wax candle, offering a clear, relatable comparison.
Why Is Candela Important?
Candela provides insights into how effectively a light source can illuminate a target area. This is particularly useful in scenarios requiring precision, such as:
- Focused Illumination: Ensures optimal light delivery in the desired direction, reducing wastage.
- Improved safety: In these areas, directional light is critical for safety. Enhanced visibility in areas such as roadways and stages.
Applications of Candela
- Automotive Headlights: Especially when driving on the road at night, you want to ensure that the road ahead is adequately illuminated. At the same time, without causing glare to oncoming vehicles.
- Flashlights: Determines beam intensity for tasks requiring focused light, such as hiking or search operations.
- Stage Lighting: Provides targeted brightness for specific areas, ensuring clarity for performers and audiences.
- Marine and Aviation Signals: Used in navigational lights to ensure signals are visible over long distances.
What Is Lux?
Lux (lx) is the SI unit of illuminance, which measures the amount of light that hits a surface. It indicates how well an area is illuminated by assessing the light intensity per square meter.
Lux (lx) is the SI unit of illuminance, which represents the luminous flux (lumens) received per unit area. That is, 1 lux is equal to the luminous flux of 1 lumen evenly distributed on a surface of 1 square meter.
Key Characteristics
- Area-Based Measurement: Lux accounts for the area over which light spreads. For example, a 100-lumen light concentrated over one square meter produces 100 lux, but the same light spread over 10 square meters results in only 10 lux.
- Real-World Relevance: Lux is crucial for assessing whether an environment has sufficient lighting for specific tasks or purposes.
Why Is Lux Important?
Lux helps determine if lighting conditions meet safety and productivity standards in various environments:
- Improved visual experience: In LED lighting design, choosing the right lux level can improve the visual experience and increase energy efficiency.
- Comfortable Ambiance: Prevents over-brightness or insufficient lighting, contributing to comfort in homes and offices.
Applications of Lux
- Workspaces: Offices often require a lux level of around 300-500 to maintain productivity without causing eye strain.
- Home lighting: Each area of a room requires a different lux level ((living room 100-300 lx, kitchen 300-500 lx)
- Street Lighting: Ensure that roads are adequately lit to enhance driver and pedestrian safety. (10-30 lx for normal streets)
- Photography and Film: Accurate lux levels are critical for achieving desired lighting effects.
What Is Lumen?
Lumen (lm) is the international unit of luminous flux, used to express the total amount of visible light emitted by a light source in all directions. It measures the total output of light, rather than the intensity of light shining on a surface.
Unlike candela, which takes direction into account, and lux, which takes surface area into account, lumen reflects the overall brightness that a light source can produce.
Key Characteristics
- Total Light Output: Lumens represent the cumulative brightness of a light source, making it the most widely used metric for comparing lighting products.
- Consumer-Oriented: Lumens are often displayed on product packaging, helping buyers understand a bulb’s brightness regardless of its power consumption (wattage).
Why Are Lumens Important?
Understanding what lumens mean can help consumers better choose lighting that meets their needs. Instead of relying solely on outdated wattage comparisons.
Lumens are different from power (wattage), which indicates energy consumption, while lumens indicate brightness. For example, a 60W incandescent bulb emits about 800 lumens, and an LED 10W bulb ≈ 800 lm (more energy-efficient).
Applications of Lumens
- Indoor Lighting: Lumens are key for selecting bulbs to illuminate living rooms, kitchens, and bedrooms.
- Outdoor Lighting: High-lumen lights are ideal for floodlights and security purposes, ensuring adequate visibility.
- Accent Lighting: LED strips with specific lumen outputs can create ambient or task lighting effects.
- Energy Efficiency: Lumens per watt (lm/W) is a measure of energy efficiency, helping consumers choose eco-friendly lighting options.
Key Differences Between Candela vs Lux vs Lumens
Understanding the distinctions between these metrics is essential for choosing the right lighting solutions:
| Metric | Measures | Example Applications |
| Candela | Light intensity in a direction | Spotlights, flashlights |
| Lux | Illuminance on a surface | Offices, roadways |
| Lumens | Total light output | General lighting, bulbs |
Candela vs. Lumens: While lumens measure total light, candela measures the intensity in one direction.
Lux vs. Lumens: Lux considers the area over which lumens are spread, making it more relevant for assessing light distribution.
How Are Candela, Lux, and Lumens Related?
These metrics are interconnected, and understanding their relationship helps in designing effective lighting systems:
- Lumens to Lux: Lux depends on the distance and spread of lumens. A high-lumen light may produce low lux if it is dispersed over a large area.
- Candela to Lux: Candela contributes to lux by determining the directional intensity reaching a surface.
Practical Example:
A 1,000-lumen light source positioned at 1 meter illuminates a 1-square-meter area with 1,000 lux. If the area increases to 10 square meters, the illuminance drops to 100 lux.
Applications of Candela, Lux, and Lumens
Different scenarios candela vs Lux vs Lumens require specific metrics:
- Candela: Ideal for focused lighting in theaters, car headlights, or lighthouses.
- Lux: Essential for workplaces, ensuring compliance with safety and productivity standards.
- Lumens: Useful for evaluating the overall brightness of a light source when selecting Led strip or fixtures.
How to Choose Lighting Based on These Metrics?
When selecting right lighting, consider the following:
- Purpose: Determine if you need focused light (candela), ambient light (lux), or total brightness (lumens).
- Environment: For large areas, prioritize high-lumen lights with a wide beam angle; for task lighting, focus on lux levels.
- Standards: Refer to lighting standards for specific applications, such as 300 lux for office desks or 20 lux for hallways.
Tips for Theoretical Analysis of Light Measurement
When discussing lighting measurement, we often come across misconceptions about the terms lumens, candela, and lux. Let’s analyze these common theories now.
1. Higher lumens do not mean better lighting
Lumens measure total light output, but they do not take into account the distribution or direction of the light. A 1,000-lumen spotlight can effectively illuminate a small, focused area, but will dim the surrounding space.
Conversely, evenly diffused light with fewer lumens can provide better overall lighting in a larger room.
2. Candela Does Not Equal Brightness
Candela measures the intensity of light in a specific direction, but does not represent total brightness. For example, a 200-candela flashlight focuses the light into a tight beam, making it appear very bright in the target area.
Floodlights with lower candela ratings spread the light over a wider area, illuminating more space, but with less directional intensity.
3. Lux is not a fixed value
Lux is a measure of illumination that depends on the distance from the light source and how the light is spread across an area.
According to the inverse square law, lux decreases as the distance from the light source increases. Similarly, a narrow beam of light will produce a higher lux value on a surface than a wide beam of light at the same distance.
Therefore, lux levels can be adjusted by changing the position, angle or type of light source. Making it a dynamic, situation-dependent measurement.
Conclusion
Understanding the differences between candela vs lux vs lumens is essential to making smart lighting choices. Each metric serves a different purpose: candela focuses on intensity, lux measures surface illuminance, and lumens indicate total brightness. Considering these metrics based on your needs, you can choose lighting that enhances functionality, safety, and aesthetics in any environment.
FAQs
I see this term whenever I choose a lighting fixture. Lumens (lm) is a measure of the total luminous flux emitted by a light source, i.e. the total output of visible light. The higher the lumen value, the brighter the light source.
Lux (lx) is a unit of illumination, which indicates the amount of light distributed over a unit area. For example, a lamp with 1000 lm evenly irradiates an area of 10 square meters, and the illumination is 100 lx.
Candela (cd) is a unit of light intensity, which indicates the amount of light emitted by a light source in a certain direction. 1 cd is equivalent to the light intensity of 1 lm in 1 steradian.
This is not necessarily the case, because lumens represent the total amount of light. However, if the light is not focused correctly or distributed unevenly, the lighting effect may not be ideal.
Car headlights need to concentrate light to a long distance, so they have high candela values (high light intensity). But due to the small beam angle, the total lumen value may not be as high as that of ordinary household bulbs.
