Chapter 1: Fundamentals of Illumination

Basic Illumination Terminology

- Luminous Flux (Φ): Total light energy emitted per second, measured in lumens (lm).

- Illuminance (E): Light falling on a surface, measured in lux (lm/m²).

- Luminance (L): Brightness perceived from a surface, measured in cd/m².

- Candela (cd): Unit of luminous intensity in a given direction.

Laws of Illumination

- Inverse Square Law: (E is inversely proportional to d^2). Illuminance decreases with the square of distance.

- Lambert’s Cosine Law: (E is proportional to cos theta). Illuminance depends on the angle of incidence.

Measurement of Illumination

- Lux Meter: Device used to measure illuminance.

- Units: 1 lux = 1 lumen/m².

Lighting Calculation Methods

- Watt/m² Method: 

  - Based on power density.  

  - Formula: Illuminance = Total Watts/Area

- Lumens or Light Flux Method: 

  - Uses lamp output and utilisation factor.  

  - Formula: E = (Φ x UF x MF)/A  

  - Where UF = Utilization Factor, MF = Maintenance Factor, A = Area.

- Point-to-Point Method:  

  - Calculates illuminance at a specific point using the inverse square law and the cosine law.

Standards for Illumination

- Offices: 300–500 lux  

- Classrooms: 250–300 lux  

- Workshops: 500–1000 lux  

- Road Lighting: 10–20 lux