SI Units – Luminous Intensity

The candela (cd) is defined by taking the fixed numerical value of the luminous efficacy of monochromatic radiation of frequency 540 × 10¹² Hz, K_cd, to be 683 when expressed in the unit lm W⁻¹, which is equal to cd sr W⁻¹, or cd sr kg⁻¹ m⁻² s³, where the kilogram, meter and second are defined in terms of h, c and ∆ν_Cs.

Radiation at frequencies other than 540 x 10¹² Hz is also measured in candelas in accordance with the standard luminous efficiency, V (λ), curve that peaks at 540 x 10¹² Hz (yellow-green). Learn more about the realization of the candela and luminance (candela per square meter).

Resources for Students and Teachers

Teachers: Top 10 Tips for Teaching the Metric System. (NIST)

Credit: ©2020 U.S. Secretary of Commerce. All Rights Reserved.

Resources for K-2

• Not sure how to tell that scientific minded person in your life how you feel? Maybe our Superhero Valentine's Day cards will do the trick.
• Download these fun coloring pages for Candela and our SI Superheroes.

 

Credit: ©2020 U.S. Secretary of Commerce. All Rights Reserved.

 

Resources for Grade 3-5

• League of SI Superheroes - Candela
  • This comic book-style video animation series has been developed to help middle school students learn about the 7 SI base measurement units.
• SI Units Card Deck (SP 1297) - this activity offers a fun way to enhance understanding of the International System of Units. (NIST)

Credit: N. Hanacek/NIST

Resources for Grade 6-8

• SI Units Card Deck (SP 1297) - this activity offers a fun way to enhance understanding of the International System of Units. (NIST)
• SI Base Units Relationship Poster (SP 1247) - a colorful poster illustrating the relationships of the International System of Units (SI) derived units with special names and symbols and the seven traditional base units. (NIST)
• Candela – Vision is perhaps the most powerful of human senses, and light one of humanity’s age-old metaphors for understanding, wisdom and truth. (NIST)
• Tour of the Electromagnetic Spectrum (NASA) – Explore how visible light works, what colors mean, and how scientists use light to study stars, planets, and Earth.
• Science of Light – Learning more about the science of light and human vision will help us understand the value and fragility of natural lights capes. (National Park Services)

Resources for Grade 9+

• SI Units Card Deck (SP 1297) - this activity offers a fun way to enhance understanding of the International System of Units. (NIST)
• SI Base Units Relationship Poster (SP 1247) - a colorful poster illustrating the relationships of the International System of Units (SI) derived units with special names and symbols and the seven traditional base units. (NIST)
• Candela – Vision is perhaps the most powerful of human senses, and light one of humanity’s age-old metaphors for understanding, wisdom and truth. (NIST)
• Tour of the Electromagnetic Spectrum (NASA) – Explore how visible light works, what colors mean, and how scientists use light to study stars, planets, and Earth.
• Lights on the International Space Station – Exploring Space Through Math. (NASA)
• Science of Light – Learning more about the science of light and human vision will help us understand the value and fragility of natural lights capes. (National Park Services)
• Measures of Brightness. (Institute of Physics)- Learn how brightness is measured using units like lumens, lux, and candela, and how these relate to human vision. This resource explains how our eyes detect light and how modern lighting is evaluated for effectiveness and visibility.

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League of SI Superheroes – Candela

This comic book-style video animation series has been developed to help middle school students learn about the 7 SI base measurement units. Don't let her small size fool you, Candela's power over light helps to brighten the whole world. A candela is a measure of brightness about equal to the light given off by a single candle.

Navigate to more SI base unit information

• SI Units
• Fundamental Physical Constants
• Length – meter (m)
• Time – second (s)
• Amount of substance – mole (mole)
• Electric current – ampere (A)
• Temperature – kelvin (K)
• Mass – kilogram (kg)

Credit: J. Wang and B. Hayes/NIST ©2020 U.S. Secretary of Commerce. All Rights Reserved.

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