Luminous quantity (Q) is a measure of the total light emitted from a light source over a given period. It is the total amount of light emitted or received by a surface in a given time period. It is measured in lumens- seconds (lm s) .
1. Formula for light energy (Q)
The luminous energy (Q) is calculated by multiplying the luminous flux (lumen) by the time the light is emitted:
whereby:
- Q = Luminous energy (lumen-seconds, lm·s)
- = Luminous flux (lumen, lm)
- t = Time (seconds, s)
📌 Luminous flux ( ) is the total amount of light emitted by the source per unit time (in lumens, lm). Time ( t ) is the duration of the exposure.
2. Units of light energy
- Lumen-second (lm·s) : The unit that measures the amount of light over a period of time. This gives the total amount of light energy emitted or received by a source.
- Joule (J) : Light energy can also be expressed in joules , since it is energy. The conversion from lumens-seconds to joules is often used in engineering calculations.
📌 1 lumen-second is equal to 1 lumen emitted for 1 second.
3. Applications of light energy (Q)
| Application | Why is light energy important? |
|---|---|
| 🏢 Lighting in buildings | Helps determine energy consumption and lighting efficiency . |
| 🎥 Film and photography | To obtain the correct exposure in scenes and shots. |
| 🌍 Sunlight | The amount of light that reaches the Earth and affects natural lighting . |
| 🚗 Car lighting | Determining the brightness of headlights for safe lighting in vehicles. |
📌 Light energy is essential for designing energy-efficient lighting and planning lighting systems.
4. Light energy and energy consumption
The amount of light energy is also often used in the context of lighting energy consumption . The more lumens a light source emits, the more light energy is produced. This affects the efficiency of the lighting system and its energy consumption .
📌 For example : LED bulbs produce more lumens per watt , meaning they deliver more light energy per unit of electricity than traditional incandescent bulbs.
💡 In short :
The quantity of light (luminous energy, Q) is the total amount of light emitted by a light source over a given period of time and is measured in lumen-seconds (lm·s) . It is important for understanding energy consumption and lighting design .