Luminous efficacy

CIE 1931 Luminosity

Luminous efficacy is a measure of how well a light source produces visible light. It is the ratio of luminous flux (measured in lumens) to power (measured in watts), and it is expressed in lumens per watt (lm/W). This metric is crucial in the fields of lighting, photometry, and energy efficiency.

Definition

Luminous efficacy can be divided into two types:

• Luminous efficacy of radiation (LER) - This is the ratio of the luminous flux to the radiant flux. It measures how well the power of electromagnetic radiation is converted into visible light.
• Luminous efficacy of a source - This is the ratio of the luminous flux emitted by a light source to the total power consumed by the source. It measures the efficiency of the light source in converting electrical power into visible light.

Calculation

The luminous efficacy of a light source is calculated using the formula:

\[ \eta = \frac{\Phi_v}{P} \]

where:

• \(\eta\) is the luminous efficacy (lm/W),
• \(\Phi_v\) is the luminous flux (lumens),
• \(P\) is the power (watts).

Factors Affecting Luminous Efficacy

Several factors can affect the luminous efficacy of a light source, including:

• The type of light source (e.g., incandescent, fluorescent, LED).
• The color temperature and color rendering index (CRI) of the light.
• The design and materials used in the light source.

Typical Values

Different types of light sources have different typical values of luminous efficacy:

• Incandescent bulbs: 10-17 lm/W
• Fluorescent lamps: 35-100 lm/W
• LEDs: 80-200 lm/W

Applications

Luminous efficacy is an important parameter in various applications, including:

• Lighting design - To choose the most efficient light sources for a given application.
• Energy conservation - To reduce energy consumption by using high-efficacy light sources.
• Environmental impact - To minimize the environmental impact of lighting by reducing energy use and associated emissions.

Related Concepts

• Luminous efficiency
• Luminous flux
• Radiant flux
• Photometry (optics)
• Color rendering index

See Also

• Lighting
• Energy efficiency
• Photometry
• Radiometry
• Color temperature