Candela

Definition

The candela (cd) is the base unit of luminous intensity in the International System of Units (SI). It is a measure of the amount of light emitted in a particular direction, and is a fundamental unit used to quantify the brightness or luminous power of a light source.

5 Must Know Facts For Your Next Test

1. The candela is defined as the luminous intensity of a source that emits monochromatic radiation of frequency 540 × 10^12 hertz and has a radiant intensity of 1/683 watt per steradian.
2. Candela is the only base unit in the SI system that is defined in terms of a specific physical measurement, rather than a fundamental physical constant.
3. Luminous intensity, measured in candelas, is a key parameter in lighting design and the evaluation of light sources, as it determines the brightness of a light source in a specific direction.
4. The candela is related to the lumen (lm) through the formula: luminous flux (lm) = luminous intensity (cd) × solid angle (sr).
5. Accurate measurement of luminous intensity is crucial in various applications, such as automotive lighting, stage lighting, and the design of energy-efficient lighting systems.

Review Questions

• Explain the relationship between luminous intensity, measured in candelas, and luminous flux, measured in lumens.
  • Luminous intensity, measured in candelas (cd), is a measure of the amount of light emitted in a particular direction. Luminous flux, measured in lumens (lm), is the total amount of light emitted by a source. The two are related by the formula: luminous flux (lm) = luminous intensity (cd) × solid angle (sr). This means that luminous intensity, or the brightness of a light source in a specific direction, is a key factor in determining the overall luminous flux or total light output of a source.
• Describe the significance of the candela as a base unit in the International System of Units (SI).
  • The candela is unique among the base units of the SI system in that it is defined in terms of a specific physical measurement, rather than a fundamental physical constant. The candela is defined as the luminous intensity of a source that emits monochromatic radiation of a specific frequency and has a radiant intensity of 1/683 watts per steradian. This precise definition allows for the accurate measurement and comparison of light sources, which is crucial in a wide range of applications, from lighting design to photometry. The candela's role as a base unit in the SI system underscores the importance of quantifying and understanding the properties of light in scientific and technological contexts.
• Evaluate the importance of accurate measurement and understanding of luminous intensity, as represented by the candela, in the design and evaluation of lighting systems and light sources.
  • The accurate measurement and understanding of luminous intensity, as represented by the candela, is essential in the design and evaluation of lighting systems and light sources. Luminous intensity directly determines the brightness of a light source in a specific direction, which is a critical parameter in applications such as automotive lighting, stage lighting, and the development of energy-efficient lighting systems. By precisely quantifying the luminous intensity of a light source using the candela, lighting designers and engineers can optimize the distribution and efficiency of light, ensuring that the desired illumination levels are achieved while minimizing energy consumption and light pollution. Furthermore, the candela's role as a base unit in the SI system allows for the standardization and comparison of light sources, enabling the development of more effective and sustainable lighting technologies. Overall, the candela's importance lies in its ability to provide a consistent and reliable measure of luminous intensity, which is fundamental to the advancement of lighting science and engineering.

Related terms

Luminous Flux: Luminous flux is the total amount of light emitted by a source, measured in lumens (lm).

Luminous Intensity: Luminous intensity is the amount of light emitted in a specific direction, measured in candelas (cd).

Illuminance: Illuminance is the amount of luminous flux falling on a surface, measured in lumens per square meter (lm/m^2) or lux (lx).