--- title: "Light sources and indoor lighting schemes" subject: "Industrial Power Distribution and Illumination" chapter: 6 key: "semester_6/industrial_power_distribution_and_illumination:light-sources-indoor-schemes" source: https://www.bctengineer.com/q/semester_6/industrial_power_distribution_and_illumination/light-sources-indoor-schemes site: BCT Engineering --- # Light sources and indoor lighting schemes Industrial Power Distribution and Illumination · Chapter 6: System Components for Industrial Illumination - Asked in: 2071 Bhadra, 8 marks - Video: [Different types of lighting scheme](https://www.youtube.com/watch?v=DzZuLREiQOg) — Polytechnic Guru - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_6/industrial_power_distribution_and_illumination/light-sources-indoor-schemes - Whole chapter: https://www.bctengineer.com/md/semester_6/industrial_power_distribution_and_illumination/chapter-6 ## Question List and explain briefly various types of lighting sources and different methods of lighting schemes used in indoor lighting. ## Short answer Common light sources are incandescent, fluorescent, CFL, HID and LED lamps. Indoor lighting schemes by light distribution are direct (90-100% downward), semi-direct, general diffusing, semi-indirect and indirect. By coverage, schemes include general, localised and emergency lighting. ## Answer #### Types of light sources 1. **Incandescent (filament) lamps:** a tungsten filament heated to about 2500–2800 °C glows. Includes GLS lamps and **tungsten-halogen** lamps (halogen gas allows higher filament temperature and longer life). Efficacy 10–25 lm/W, excellent colour rendering (Ra ≈ 100), cheap but short life (1000–2000 h). 2. **Low-pressure discharge lamps:** - **Fluorescent tube (FTL)** and **compact fluorescent lamp (CFL):** mercury vapour discharge produces UV, which phosphor coating converts to visible light. 50–90 lm/W, life 8000–15000 h, need ballast. - **Low-pressure sodium (LPS):** monochromatic yellow light, very high efficacy (up to 180 lm/W) but very poor colour rendering. 3. **High-intensity discharge (HID) lamps:** **high-pressure mercury vapour** (35–60 lm/W), **high-pressure sodium** (80–140 lm/W, golden-yellow), **metal halide** (70–110 lm/W, white light, good CRI). Used for streets, high-bay factories and floodlights. 4. **Solid-state lighting – LED:** semiconductor p-n junction emits light when forward biased. Efficacy 100–200 lm/W, life 25,000–50,000 h, instant start, dimmable, no mercury. Now the most used source for all applications. 5. **Others:** induction lamps (electrodeless, very long life), neon lamps for signs. #### Lighting schemes for indoor lighting Based on how much of the luminaire's light goes directly downward to the working plane: | Scheme | Light directed downward | Features | Use | |---|---|---|---| | Direct | 90–100 % | Most efficient; harsh shadows, glare possible | Factories, workshops | | Semi-direct | 60–90 % | Some light to ceiling softens shadows | Offices, classrooms | | General diffusing | 40–60 % | Light equally up and down | Shops, homes | | Semi-indirect | 10–40 % | Mostly reflected from ceiling; soft light | Lounges, hotels | | Indirect | 0–10 % | All light from ceiling; no glare, least efficient | Cinemas, decorative | By coverage, indoor lighting is also arranged as **general lighting** (uniform over the whole area), **localised lighting** (extra light on specific work points), and **general plus local** lighting, with emergency lighting for safety. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Which describes incandescent lamps? A. Efficacy 100-200 lm/W, life 50,000 h B. Tungsten filament, 10-25 lm/W, excellent colour rendering but short life C. Mercury discharge with phosphor D. Monochromatic yellow Answer: B. Filament lamps are cheap with Ra about 100 but inefficient and short-lived (1000-2000 h). (Key point: Incandescent) 2. How does a fluorescent lamp produce visible light? A. Filament glows B. Mercury discharge produces UV, converted by phosphor coating to visible light C. Semiconductor junction emits light D. Arc in sodium at high pressure Answer: B. UV from mercury vapour excites the phosphor, which fluoresces; a ballast is needed. (Key point: Fluorescent working) 3. Which scheme directs 90-100 % of light downward, and what is its drawback? A. Indirect, causing no glare B. Direct, most efficient but with harsh shadows and possible glare C. Semi-indirect, for cinemas D. General diffusing, with ceiling reflection only Answer: B. Direct lighting is most efficient (used in factories) but gives harsh shadows and glare. (Key point: Direct scheme) 4. Which is true of indirect lighting? A. 0-10 % downward, all from ceiling, no glare but least efficient B. 90-100 % downward C. Most efficient scheme D. Used only in workshops Answer: A. Indirect lighting reflects all light from the ceiling: soft and glare-free, but least efficient. (Key point: Indirect scheme) ## Related in Industrial Power Distribution and Illumination - [Lighting schemes: local, general, emergency](https://www.bctengineer.com/question.md?key=semester_6%2Findustrial_power_distribution_and_illumination%3Alighting-schemes-local-general-emergency) — Industrial Power Distribution and Illumination, chapter 7, asked 2× - [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 - [Factors for street and flood lighting design](https://www.bctengineer.com/question.md?key=semester_6%2Findustrial_power_distribution_and_illumination%3Aflood-street-design-factors) — Industrial Power Distribution and Illumination, chapter 8, asked 2× - [Industry room 30 × 20 m LED lighting and DB](https://www.bctengineer.com/question.md?key=semester_6%2Findustrial_power_distribution_and_illumination%3Aindustry-room-30x20-led) — Industrial Power Distribution and Illumination, chapter 7, asked 2× - [Conference hall 2×36 W CFL lighting](https://www.bctengineer.com/question.md?key=semester_6%2Findustrial_power_distribution_and_illumination%3Aconference-hall-cfl) — Industrial Power Distribution and Illumination, chapter 7 - [Flood lighting a 50 × 16 m building](https://www.bctengineer.com/question.md?key=semester_6%2Findustrial_power_distribution_and_illumination%3Afloodlight-building-50x16) — Industrial Power Distribution and Illumination, chapter 8 ## Related in other subjects - [Types of lighting sources](https://www.bctengineer.com/question.md?key=semester_5%2Fcomputer_graphics%3Alight-source-types-effect) — Computer Graphics, chapter 8 - [Indoor air pollutants and their sources](https://www.bctengineer.com/question.md?key=semester_7%2Fenvironment_and_pollution_control%3Aindoor-air-pollutants-sources) — Environment and Pollution Control, chapter 3 - [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