Lamp Performance Parameters: Luminous Efficacy Correlated Colour Temperature Colour Rendering Index

Key learnings:
  • Luminous Efficacy Definition: Luminous efficacy is the measure of how much light a lamp produces per unit of power consumed, defined as lumens per watt.
  • Energy Efficiency: Fluorescent lamps are more energy-efficient than incandescent lamps, with higher luminous efficacy.
  • LED Efficiency: LED lamps can achieve up to 200 lumens per watt, making them highly efficient light sources.
  • Correlated Colour Temperature (CCT): CCT indicates the color of light emitted by a lamp, measured in Kelvin, with different ranges for warm, neutral, and cool white light.
  • Colour Rendering Index (CRI): CRI measures how accurately a lamp reproduces colors compared to natural light, with incandescent and halogen lamps having a CRI of 100.

Luminous Efficacy

Luminous efficacy is defined as the amount of light a lamp produces per unit of electric power consumed, measured in lumens per watt. It indicates how energy-efficient a lamp is, and this efficiency varies by type of lamp.

Incandescent lamps have a luminous efficacy of about 10-20 lumens per watt, while fluorescent lamps range from 60-100 lumens per watt, making them more energy-efficient. New LED lamps can reach up to 200 lumens per watt.

Correlated Colour Temperature

Correlated Colour Temperature (CCT) is defined as the temperature at which a heated black body emits the same color of light as the lamp.

The Unit of CCT is Kelvin. Suppose the CCT of the fluorescent lamp is 4500K; this means that if a black body is heated to 4500K, it will emit the same color of radiation or light as that of the fluorescent lamp.

Lamps are categorized by CCT into warm white, neutral white, or cool white. Lamps with a CCT below 3000K emit a yellowish-reddish light, creating a warm ambiance and are called warm white.

Lamps with a CCT between 3000K and 4000K emit white light and are known as neutral white.

If the CCT is more than 4000K, the lamp gives a whitish color of light which provides a cool feeling to its surroundings. So lamps having CCT more than 4000K are termed as cool white.

Colour Rendering Index

All objects have a particular color when viewed under natural light. If the same object is viewed under an artificial light source, the lamp reproduces the color of the object, but the color may or may not be the same as that under natural light.

Color rendering index (CRI) is the fraction with which the original color of the object is reproduced by the lamp. CRI of most lamps is less than 100%. Only incandescent lamps and halogen lamps have a CRI of 100.
Colour Rendering Index

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