Candela vs. Lux vs. Lumens: Key Differences in Light Measurement
When selecting a lighting fixture or flashlight, understanding how brightness is measured is crucial. Three primary units—lumens, candela, and lux—define different aspects of light output, intensity, and distribution. This guide explains each measurement and its significance to help you make an informed decision.
---
1. What Are Lumens?
Lumens (lm) measure the total amount of visible light emitted from a source. The higher the lumens, the brighter the light.
Unlike candela, which measures intensity in a specific direction, lumens account for all the light emitted in every direction. For example, a 3-candela (CD) light source produces approximately 38 lumens in an unobstructed setting. However, if half of the source is covered, the candela remains constant, but the lumens decrease by 50% since less total light is emitted.
Lumens have been the standard unit for measuring luminous flux since 1930 and are widely used today in lighting specifications.
2. What Is Candela?
Candela (CD) measures the intensity of light in a specific direction. It indicates how bright a light source appears from a given distance.
Candela is often referred to as candlepower, as one candela is approximately equivalent to the light output of a single candle.
Unlike lumens, which measure total light output, candela focuses on how concentrated the light is. Products such as spotlights and laser pointers have high candela ratings because they direct light in a focused beam. Even if part of the light is obstructed, the remaining visible portion retains the same intensity from a distance.
---
3. What Is Lux?
Lux (lx) measures the amount of light that falls on a specific surface area. One lux is equal to one lumen per square meter.
Lux is an essential metric for evaluating lighting conditions in various environments. Because light spreads over a surface, lux values change with distance:
- A 500-lumen spotlight illuminating 1 square meter = 500 lux.
- If the same light spreads over 5 square meters, the lux decreases to 100.
Here are some real-world lux comparisons:
- 1 lux = Twilight or moonlight
- 100 lux = Overcast day
- 400-500 lux = Standard office lighting
- 10,000 - 25,000 lux = Full daylight
- 100,000 lux = Direct sunlight
4. Understanding the Relationship Between Candela, Lumens, and Lux
4.1 Candela vs. Lumens
- Lumens represent total light output.
- Candela measures how intense the light appears in a specific direction.
For example, a high-lumen floodlight illuminates a large area, while a high-candela spotlight produces a concentrated beam visible from a distance. 1 candela is approximately equal to 12.57 lumens.
When comparing lighting products, it is best to evaluate candela vs. candela or lumens vs. lumens, rather than attempting to directly correlate the two.
4.2 Lux vs. Lumens
- Lumens measure the total light emitted.
- Lux measures how much of that light reaches a specific area.
A high-lumen light placed far away may not provide sufficient lux because the light disperses over a larger area. Conversely, when positioned closer, the lux value increases due to greater light concentration on a surface.
5. Key Takeaways
- Candela quantifies the intensity of light in a given direction.
- Lux indicates how much light reaches a specific area.
- Lumens measure the total light output from a source.
By understanding these distinctions, you can select the most suitable lighting solution for your needs, whether for general illumination, focused task lighting, or high-intensity applications.
