Basic Concept of Lighting

Lighting isn’t just about brightness. It’s about how light is measured, how it feels, and how it affects the spaces we live and work in. Whether you’re an architect, designer, or just curious about the science of light, here are some important terms explained in simple words.

1. Luminous Flux

This refers to the total amount of visible light emitted by a source in one second. Think of it as the overall light output.

2. Luminous Intensity

Not all light spreads evenly. Luminous intensity measures the power of light in a specific direction, adjusted for how sensitive the human eye is to different wavelengths.

• SI unit: Candela (cd)

3. Illuminance

Illuminance is about the amount of light falling on a surface. It tells you how bright a table, wall, or floor appears when light lands on it.

• In simple terms: luminous flux per unit area.

4. Color Temperature

Ever noticed how some lights feel warm and cozy while others feel cool and sharp? That’s color temperature.

• It’s based on the temperature of an ideal black-body radiator that produces similar light.
• Lower temperature (e.g., 2700K) → More red/yellow → Warm white (like incandescent bulbs).
• Higher temperature (e.g., 6000K) → More blue → Cool white (like daylight lamps).

5. Color Rendering Index (CRI)

CRI tells you how accurately a light source shows colors compared to natural light.

• A high CRI means objects look true to their real color.
• Important for photography, cinematography, and design.

6. Luminaire Efficiency

This measures how well a lighting fixture (luminaire) uses the light from its lamp(s).

• Formula: Luminous flux emitted by the luminaire ÷ Luminous flux of the lamp(s)
• Higher efficiency = better energy savings.

7. Glare

Glare is the excessive brightness that causes discomfort. It can distract, reduce visibility, or simply annoy the eyes.

• Can come from direct light (looking at a bulb) or indirect reflections (light bouncing off shiny surfaces).

8. Beam Angle

Beam angle defines how wide the light spreads from a source.

• It’s the angle between two directions where the light intensity drops to 10% of its maximum.
• A narrow beam highlights specific areas, while a wide beam spreads light across a larger space.

✅ With these terms in mind, you’ll better understand how lighting affects not only visibility but also mood, comfort, and energy efficiency.