Candela

What does Candela mean?

The candela (CD) is the base unit of luminous intensity in the International System of Units (SI). It is defined as the luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency 540 × 10^12 hertz and that has a radiant intensity in that direction of 1/683 watt per steradian.

In simpler terms, the candela is a measure of the brightness of a light source. It is used to quantify the amount of light emitted by a source in a particular direction. The candela is a fundamental unit in photometry, the science of measuring light. It is used in various applications, including lighting design, photography, and colorimetry.

Applications

The candela is a crucial unit in various technological fields, particularly in lighting and illumination. It is used to:

• Quantify light intensity: The candela allows engineers and lighting designers to measure the brightness of light sources, ensuring proper illumination levels in various environments, from indoor spaces to outdoor lighting.
• Design lighting fixtures: Lighting fixtures are designed using candelas to determine the appropriate light Output and Distribution patterns for different applications. This helps optimize lighting efficiency and visual comfort.
• Calibrate photometers: Photometers, devices used to measure light intensity, are calibrated using candela-rated light sources. This ensures accurate measurements of light levels in various settings.
• Specify light sources: The candela is used to specify the luminous intensity of light sources, such as lamps and LEDs. This information helps users select appropriate light sources for their desired applications.
• Photography: In photography, the candela is used to measure the brightness of light sources used for illumination. This helps photographers adjust exposure settings to Capture images with optimal brightness and contrast.

History

The concept of luminous intensity has been studied for centuries, but the standardization of the candela as the SI base unit is a relatively recent development. The history of the candela can be traced back to:

• 1760: Johann Heinrich Lambert introduced the concept of luminous intensity and proposed a unit based on the brightness of a standard candle.
• 1881: The International Electrical Congress adopted the “candle power” as a unit of luminous intensity.
• 1948: The ninth General Conference on Weights and Measures (CGPM) defined the candela as the luminous intensity of a blackbody at the freezing point of platinum.
• 1979: The 16th CGPM redefined the candela based on its Current definition using monochromatic radiation at a specific frequency. This definition aimed for greater precision and reproducibility.

The candela has undergone several refinements over time to improve its accuracy and align with advancements in photometry. Today, it remains a fundamental unit used worldwide for measuring and specifying light intensity in various technological applications.