What is Quantity of Light

Horace He

Last Updated: August 7, 2023

What is Quantity of Light

Quantity of light refers to the measurement and evaluation of the amount of light emitted by a lamp or lighting system. It is a metric used to understand and predict the performance of a lighting system. The quantity of light is determined by two main factors: luminous flux and illuminance.

  • Luminous flux represents the quantity of light that leaves the lamp and is measured in lumens (lm). It indicates the total amount of light produced by the lamp once it has stabilized. Lamps are typically rated in terms of initial lumens, which indicate the light output once the lamp has stabilized, and mean lumens, which represent the average light output over the lamp’s rated life.
  • Illuminance, on the other hand, refers to the amount of light measured on the workplane in the illuminated space. It is measured in footcandles (fc) or lux (in metric). Footcandles represent the density of light per square foot, while lux represents the density of light per square meter. Light levels can be calculated or measured using a light meter. Initial footcandles indicate the light level after new lamps are installed, while maintained footcandles take into account factors such as light loss over time.

The quantity of light can be influenced by various factors, including lamp lumen depreciation, the interaction between the lamp and the ballast, voltage variations, dirt or dust on the lamp, and the ambient temperature in the fixture. These factors can affect the overall performance and output of the lighting system.

The quantity of light in lighting design ensures the optimal light levels for different tasks and activities. Exceeding or falling below the recommended light levels can impact visual comfort and task performance. By understanding and controlling the quantity of light, lighting professionals can create well-lit environments that meet the specific needs and requirements of the space.

Frequently Asked Questions

What Are the Two Characteristics of Light Quality

When it comes to light quality, there are two main characteristics that are commonly considered: Correlated Color Temperature (CCT) and Color Rendering Index (CRI). These two measures provide a comprehensive understanding of the majority of light sources available.

What Are the Six Qualities of Light

Photographers can manipulate and combine the qualities of light, such as angle, size, distance, shape, duration, and color, to create a desired impact in their photographs, going beyond mere illumination.

What Light Level Is Dark

The light level of 0 indicates darkness, while a light level of 255 represents bright light.