---
title: "Types of lighting sources"
subject: "Computer Graphics"
chapter: 8
key: "semester_5/computer_graphics:light-source-types-effect"
source: https://www.bctengineer.com/q/semester_5/computer_graphics/light-source-types-effect
site: BCT Engineering
---

# Types of lighting sources

Computer Graphics · Chapter 8: Illumination and Surface Rendering methods

- Asked in: 2072 Chaitra, 3 marks
- Video: [OpenGL Tutorial 11 - Types of Light](https://www.youtube.com/watch?v=JB4d1yXZ-yA) — Victor Gordan
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_5/computer_graphics/light-source-types-effect
- Whole chapter: https://www.bctengineer.com/md/semester_5/computer_graphics/chapter-8

## Question

Explain about different types of lighting sources and how these light sources affect the illumination model.

## Short answer

Point, directional, spotlight, area, and ambient light. These determine L and intensity. Point source L varies and attenuates; directional L is constant, no attenuation; spotlight has cone falloff. The model sums attenuated terms per source, plus constant ambient. Soft shadows from area sources.

## Answer

Light sources used in computer graphics:

1. **Point source:** emits light equally in all directions from a single position (like a bulb). L differs for each surface point, and the light is attenuated with distance by f(d).
2. **Directional (infinite, distant) source:** a point source very far away (like the sun). All rays are parallel, so L is the same for the whole scene and there is no distance attenuation.
3. **Spotlight:** a point source with a direction and a cone of half-angle θ_l. The intensity is greatest along the cone axis and falls off towards the edge of the cone: I ∝ cos^a(α), where α is the angle from the cone axis. There is no light outside the cone (α > θ_l).
4. **Area (distributed) source:** light comes from a surface of finite size (such as a tube light), giving soft shadows. It is modelled as many point sources.
5. **Ambient light:** uniform, non-directional light that comes from the surroundings.

**Effect on the illumination model**
- The light direction L, used in the diffuse term (N·L) and the specular term, depends on the source position (for a point source) or is constant (for a directional source).
- The intensity IL is modified by the attenuation f(d) for point sources and by the angular factor for spotlights.
- Contributions from several sources are added: I = ka·Ia + Σ f(d_l)·IL_l·[kd (N·L_l) + ks (N·H_l)^n].
- Ambient light adds a constant term ka·Ia.
- The type of source also affects shadows and highlights.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. What is true of a directional (distant) light source?
   A. All rays are parallel, so L is the same everywhere and there is no distance attenuation
   B. L differs at each surface point and intensity falls as 1/d^2
   C. It emits only inside a cone
   D. It lights all surfaces equally with no direction
   Answer: A. A very distant source like the sun has constant L and f(d) = 1. (Key point: Directional source)

2. How does a spotlight differ from a point source?
   A. It is a uniform non-directional source
   B. It has a direction and a cone; intensity falls off with the angle from the axis and is zero outside the cone
   C. It is located at infinity with parallel rays
   D. It is a finite-sized surface giving soft shadows
   Answer: B. A spotlight is a point source with an axis and cone angle, with I proportional to cos^a(alpha) inside the cone. (Key point: Spotlight)

3. How does the type of light source affect the illumination model?
   A. It changes only the ambient coefficient ka
   B. It changes the shininess exponent n
   C. It changes L in the N.L and specular terms and modifies IL through attenuation or angular factors
   D. It has no effect except on shadows
   Answer: C. Source position determines L, and attenuation or the spotlight factor modifies IL; multiple sources are summed. (Key point: Effect on model)

## Related in Computer Graphics

- [Phong illumination model expression](https://www.bctengineer.com/question.md?key=semester_5%2Fcomputer_graphics%3Aphong-illumination-model-derive) — Computer Graphics, chapter 8, asked 8×
- [General illumination model](https://www.bctengineer.com/question.md?key=semester_5%2Fcomputer_graphics%3Ageneral-illumination-model) — Computer Graphics, chapter 8
- [Define illumination and surface rendering](https://www.bctengineer.com/question.md?key=semester_5%2Fcomputer_graphics%3Adefine-illumination-rendering) — Computer Graphics, chapter 8, asked 3×
- [Polygon tables to model Dharahara](https://www.bctengineer.com/question.md?key=semester_5%2Fcomputer_graphics%3Apolygon-vertex-edge-table-dharahara) — Computer Graphics, chapter 6

## Related in other subjects

- [Light sources and indoor lighting schemes](https://www.bctengineer.com/question.md?key=semester_6%2Findustrial_power_distribution_and_illumination%3Alight-sources-indoor-schemes) — Industrial Power Distribution and Illumination, chapter 6
- [Light sources and specular reflection principle](https://www.bctengineer.com/question.md?key=semester_6%2Findustrial_power_distribution_and_illumination%3Alight-sources-specular-reflection) — Industrial Power Distribution and Illumination, chapter 6
- [Short note: Light sources in optical communication](https://www.bctengineer.com/question.md?key=semester_6%2Fpropagation_and_antenna%3Alight-sources-short-note) — Propagation and Antenna, chapter 6
- [WDM and its light sources](https://www.bctengineer.com/question.md?key=semester_8%2Ftelecommunications%3Awdm-light-sources) — Telecommunications, chapter 3