Candela: Origin & Measurements

Content Curator

Candela is the SI Unit of luminous intensity - a measure of wavelength weighted power emitted by a source light. Light is measured in a number of ways even though light is not a physical quantity. However, light has various physical properties like speed, wavelength etc. that can be measured in terms of various units such as candela, lux and lumen. The candela is said to have replaced the standard candle or lamp as a unit of luminous intensity in calculations and derivations involving artificial light.

Table of Contents

Definition of Candela
Origin of Candela
Other Measures of Light
Things to Remember
Previous Year Questions
Sample Questions

Key words: Candela, Unit of measurement, Unit of Light, Luminous intensity, SI Unit

Definition of Candela

[Click Here for Previous Year Questions]

In the field of physics, the Candela, denoted by the symbol ‘cd/m²’, can be defined as the unit of luminous intensity i.e. a measure of the wavelength weighted power emitted by a source of light. According to the International System of Units, popularly known as SI, the candela is a base unit that can be defined by taking the fixed value in numerical terms of the luminous efficacy of the monochromatic radiation having a frequency of 540 x 10¹² Hertz.

One candela is mathematically expressed as: 1 cd = (Kcd/ 683) Kgm²s^-3sr^-1

The unit is dependent on luminous intensity and radiant intensity for a given wavelength of light. Luminance is measured in lux, which is defined as one candela per square meter.

candela

Learn More About:

Important Concepts Related to this Topic
Unit of Light	System of Units	SI Units

Origin of Candela

[Click Here for Sample Questions]

Candela originates from the latin word that translates to “candle” that refers to an ancient light source. In olden times, Candlepower was used to define luminous intensity depending on the candle.

The candela was first defined by French Physicist and inventor, Jules Violle. In 2018, the 26th general conference introduced candela as the official unit of measurement of luminous intensity.

Other Measures of Light

[Click Here for Previous Year Questions]

The two other main measures of light are: Lumen and Lux.

Lumen is the SI unit of luminous flux, which refers to the rate at which the visible light is emitted from a source. The lumen, in relation to the candela, is defined as:

1lm= 1cd . sr

Where, lm = lumen

Cd = candela

Sr = steradian

Lux is the SI unit of illuminance and luminous emittance. Lux is related to lumen in a way that one lux is equivalent to lumen per square meter and is given by:

1 lx= 1 lm/m² = 1 cd.sr/m²

Light

Things to Remember

Candela is the SI unit of luminous intensity.
Candela is denoted by ‘cd/m²’.
It is the luminous power per unit solid angle emitted by a point light source in a specified direction.
Luminous intensity is comparable to radiant intensity.
Candela has originated from a Latin word which means “candle”.
It is mathematically expressed as 1 cd = (Kcd/ 683) Kgm²s^-3sr^-1.

Do Check Out:

Important Concepts Related to this Topic
Measurements of Length	Unit of Sound	Precision of a measurement
The International System of Units	Unit of Resistance	Uncertainty in Measurement
Unit Conversion	Unit of Force	Unit of Time

Previous Year's Questions

If the magnetic flux is represented in weber, then the unit of magnetic induction…? (GUJCET 2006)
Which of the following dimensions will be the same as that of time…? (NEET 1996)
The dimensions of impulse are equal to that of…? (NEET 1996)
Lumen is the unit of…? (UPSEE 2019)
A body weighs 22.42 g and has a measured volume of 4.7 cc The possible errors in the measurement of mass and volume…? (WBJEE 2010)
A screw gauge has a least count of 0.01 mm and there are 50 divisions in its circular scale…? (NEET 2020)
A physical quantity of the dimensions of length that can be formed out of c, G and…? (NEET 2017)
Dimensions of resistance in an electrical circuit, in terms of dimension of mass M…? (NEET 2007)
The unit of electrical power is…? (KCET 1993)
Light year is used to measure…? (DUET 2007)
What is dimensional formula of thermal conductivity…? (DUET 2006)
Which of the following is the smallest unit…? (UPSEE 2010)
‘Raman frequencies’ refers to…? (COMEDK UGET 2008)

Sample Questions

Ques: What is the origin of Candela? (3 marks)

Ans: Candela was first defined by French Physicist and inventor, Jules Violle. Candela originates from the latin word that translates to “candle” that refers to an ancient light source. In 2018, the 26th general conference introduced candela as the official unit of measurement of luminous intensity.

Ques: Define Candela. (2 marks)

Ans: Candela is the SI unit of luminous intensity. It is the luminous power per unit solid angle emitted by a point light source in a specified direction. It is represented as cd/m2.

Ques What is the basic unit of light? (2 marks)

Ans: The behavior of light can be seen in the behavior of waves and photons, the basic unit of light. A wavelength, which varies inversely with frequency, manifests itself as color, whilst wave amplitude is seen as luminous intensity or brightness; it is measured by the standard unit of a candela.

Ques: How accurate is the measurement of Candela? (3 marks)

Ans: Candela is a SI unit that mostly depends on human perception, hence its accuracy is not that high. The measurement laboratory is trying to reduce this uncertainty in luminous intensity management. It is estimated that the accuracy of a candela is less than 0.1%. However, it is important to improve this percentage as a SI unit should have high accuracy due to its many industrial applications.

Ques: How to increase the accuracy of Candela? (3 marks)

Ans: The national measurement laboratory, NIST is finding ways to improve the accuracy of candela. It has listed a number of ways such as developing a pulsed laser that can be tuned to particular wavelengths of light, which will further allow the creation of photometers that mimic the human vision mechanism.

Read More:

Class 11 & 12 PCMB Study Guides
NCERT Solutions for Class 12 Physics	Class 12 Physics Notes	Formulas in Physics
Topics for Comparison in Physics	Choice based questions in physics	Topics with relation in physics
Physics Study Notes	Class 12 Physics Book PDF	Class 12 Physics Practicals
Important Derivations in Physics	SI units in Physics	Important Physics Constants and Units
Class 12 Physics Syllabus	NCERT Solutions for Class 12 Chemistry	NCERT Solutions for Class 12 Biology
NCERT Solutions for Class 12 English	NCERT Solutions for Class 12 Maths	Class 12 Chemistry Practicals
Class 12 Chemistry Notes	Class 12 Biology Notes	Class 12 Maths Notes
Class 12 PCMB Notes	NCERT Class 12 Biology Book	NCERT Class 12 Maths Book
NCERT Class 12 Textbooks	NCERT Solutions for Class 11 Maths	NCERT Solutions for Class 11 Physics
NCERT Solutions for Class 11 Chemistry	NCERT Solutions for Class 11 Biology	NCERT Solutions for Class 11 English
NCERT Class 11 Chemistry Book	NCERT Class 11 Physics Book	NCERT Class 11 Biology Book
Class 11 Notes	Important Maths Formulas	Important Chemistry Formulas
Class 11 PCMB Syllabus	Chemistry Study Notes	Biology Study Notes
Periodic Table in Chemistry	Important Chemical Reactions	Comparison topics in Chemistry
Comparison Topics in Maths	Comparison Topics in Biology	Important Named Reactions
Maths MCQs	Biology MCQs	Chemistry MCQs

Candela: Origin & Measurements

Definition of Candela

Origin of Candela

Other Measures of Light

Things to Remember

Previous Year's Questions

Sample Questions

CBSE CLASS XII Related Questions

1.
Suppose a pure Si crystal has \( 5 \times 10^{28} \) atoms per \( \text{m}^3 \). It is doped with \( 5 \times 10^{22} \) atoms per \( \text{m}^3 \) of Arsenic. Calculate majority and minority carrier concentration in the doped silicon. (Given: \( n_i = 1.5 \times 10^{16} \, \text{m}^{-3} \))

2.
Two thin lenses of focal length \( f_1 \) and \( f_2 \) are placed in contact with each other coaxially. Prove that the focal length \( f \) of the combination is given by \[ f = \frac{f_1 f_2}{f_1 + f_2}. \]

3.
Photoemission of electrons occurs from a metal (\( \phi_0 = 1.96 \, \text{eV} \)) when light of frequency \( 6.4 \times 10^{14} \, \text{Hz} \) is incident on it. Calculate: Energy of a photon in the incident light, The maximum kinetic energy of the emitted electrons, and The stopping potential.

4.
Two small identical metallic balls having charges \( q \) and \( -2q \) are kept far at a separation \( r \). They are brought in contact and then separated at distance \( \frac{r}{2} \). Compared to the initial force \( F \), they will now:

5.
The figure shows three point charges kept at the vertices of triangle ABC. The net electric field, due to this system of charges, at the midpoint M of base BC will be:

6.
A tank is filled with a liquid to a height of \( 12.5 \, \text{m} \). The apparent depth of a needle lying at the bottom of the tank is measured to be \( 9.0 \, \text{m} \). Calculate the speed of light in the liquid.

Similar Physics Concepts

Comments

SUBSCRIBE TO OUR NEWS LETTER

Candela: Origin & Measurements

Definition of Candela

Origin of Candela

Other Measures of Light

Things to Remember

Previous Year's Questions

Sample Questions

CBSE CLASS XII Related Questions

1.Suppose a pure Si crystal has \( 5 \times 10^{28} \) atoms per \( \text{m}^3 \). It is doped with \( 5 \times 10^{22} \) atoms per \( \text{m}^3 \) of Arsenic. Calculate majority and minority carrier concentration in the doped silicon. (Given: \( n_i = 1.5 \times 10^{16} \, \text{m}^{-3} \))

2.Two thin lenses of focal length \( f_1 \) and \( f_2 \) are placed in contact with each other coaxially. Prove that the focal length \( f \) of the combination is given by \[ f = \frac{f_1 f_2}{f_1 + f_2}. \]

3.Photoemission of electrons occurs from a metal (\( \phi_0 = 1.96 \, \text{eV} \)) when light of frequency \( 6.4 \times 10^{14} \, \text{Hz} \) is incident on it. Calculate: Energy of a photon in the incident light, The maximum kinetic energy of the emitted electrons, and The stopping potential.

4.Two small identical metallic balls having charges \( q \) and \( -2q \) are kept far at a separation \( r \). They are brought in contact and then separated at distance \( \frac{r}{2} \). Compared to the initial force \( F \), they will now:

5.The figure shows three point charges kept at the vertices of triangle ABC. The net electric field, due to this system of charges, at the midpoint M of base BC will be:

6.A tank is filled with a liquid to a height of \( 12.5 \, \text{m} \). The apparent depth of a needle lying at the bottom of the tank is measured to be \( 9.0 \, \text{m} \). Calculate the speed of light in the liquid.

Similar Physics Concepts

Comments

SUBSCRIBE TO OUR NEWS LETTER

1.
Suppose a pure Si crystal has \( 5 \times 10^{28} \) atoms per \( \text{m}^3 \). It is doped with \( 5 \times 10^{22} \) atoms per \( \text{m}^3 \) of Arsenic. Calculate majority and minority carrier concentration in the doped silicon. (Given: \( n_i = 1.5 \times 10^{16} \, \text{m}^{-3} \))

2.
Two thin lenses of focal length \( f_1 \) and \( f_2 \) are placed in contact with each other coaxially. Prove that the focal length \( f \) of the combination is given by \[ f = \frac{f_1 f_2}{f_1 + f_2}. \]

3.
Photoemission of electrons occurs from a metal (\( \phi_0 = 1.96 \, \text{eV} \)) when light of frequency \( 6.4 \times 10^{14} \, \text{Hz} \) is incident on it. Calculate: Energy of a photon in the incident light, The maximum kinetic energy of the emitted electrons, and The stopping potential.

4.
Two small identical metallic balls having charges \( q \) and \( -2q \) are kept far at a separation \( r \). They are brought in contact and then separated at distance \( \frac{r}{2} \). Compared to the initial force \( F \), they will now:

5.
The figure shows three point charges kept at the vertices of triangle ABC. The net electric field, due to this system of charges, at the midpoint M of base BC will be:

6.
A tank is filled with a liquid to a height of \( 12.5 \, \text{m} \). The apparent depth of a needle lying at the bottom of the tank is measured to be \( 9.0 \, \text{m} \). Calculate the speed of light in the liquid.