--- title: "Factors for street and flood lighting design" subject: "Industrial Power Distribution and Illumination" chapter: 8 key: "semester_6/industrial_power_distribution_and_illumination:flood-street-design-factors" source: https://www.bctengineer.com/q/semester_6/industrial_power_distribution_and_illumination/flood-street-design-factors site: BCT Engineering --- # Factors for street and flood lighting design Industrial Power Distribution and Illumination · Chapter 8: Outdoor Lighting Design - Asked in: 2072 Magh, 8 marks; 2071 Magh, 8 marks (asked 2 times) - Video: [ILLUMINATION ENGINEERING - PART -12 - FLOOD LIGHTING - IMPORTANT TERMS & PRBOLEMS](https://www.youtube.com/watch?v=xOpYxgnD9kg) — zenmurali Sachithanandam - 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/flood-street-design-factors - Whole chapter: https://www.bctengineer.com/md/semester_6/industrial_power_distribution_and_illumination/chapter-8 ## Question With an example, explain the various factors to be taken into account for designing schemes for flood lighting and street lighting system. ## Short answer Floodlighting factors: required illumination, area, beam spread, projector distance (0.7-1×height), utilization factor, waste light factor, depreciation factor. Example: 40m×12m wall at 80 lux needs 4×400W projectors. Street lighting factors: road class, width, mounting height, spacing (S/h~3-4), lamp type, utilization and maintenance factors. Example: 10m road at 10 lux gives 28m spacing with 9000 lm LEDs. ## Answer Floodlighting and street lighting are both outdoor schemes, but floodlighting lights **vertical surfaces or large areas** with concentrated beams from projectors, while street lighting lights a **long horizontal road surface** from poles. #### Factors for floodlighting design 1. **Illumination level required** – depends on the brightness of surroundings and reflectance of the surface (light surfaces in dark surroundings need 50–100 lux; dark surfaces in bright city areas 200–400 lux). 2. **Area to be lit** (A = length × height of the face). 3. **Type of projector and beam spread** – narrow (< 25°), medium (25–40°) or wide (> 40°) depending on distance from the surface. 4. **Location and distance of projectors** – usually 0.7–1 times the height of the building; avoid glare to the public. 5. **Coefficient of utilisation (beam factor)** – fraction of lamp lumens in the beam (0.3–0.6). 6. **Waste light factor** – light spilling past edges (1.2 for regular surfaces, 1.5 for irregular objects). 7. **Depreciation / maintenance factor** – dirt on glass and lamp ageing. 8. **Lamp type, wattage and efficacy**, colour of light for good appearance. **Example (floodlighting):** A 40 m × 12 m building front needs 80 lux; CU = 0.5, DF = 1.3, WLF = 1.2; 400 W metal-halide projectors of 80 lm/W are used. ```text Area = 40 × 12 = 480 m² Total lm = E·A·DF·WLF / CU = 80 × 480 × 1.3 × 1.2 / 0.5 = 119 808 lm Lamp lm = 400 × 80 = 32 000 lm N = 119 808 / 32 000 = 3.74 → 4 ``` So 4 projectors of 400 W are used. #### Factors for street lighting design 1. **Road class and traffic** – required average illuminance and uniformity. 2. **Road width** – decides single-side, staggered or opposite arrangement. 3. **Mounting height (h)** and **spacing (S)** – S/h ratio about 3–4. 4. **Type of lamp** – HPSV, LED; efficacy and life. 5. **Luminaire distribution** – cut-off type to reduce glare. 6. **Coefficient of utilisation and maintenance factor.** 7. **Road surface reflection** and weather conditions. 8. **Special locations** – bends, junctions, bridges. **Example (street lighting):** A road 10 m wide needs 10 lux average. LED lanterns of 9000 lm, CU = 0.4, MF = 0.8 are used. ```text S = F·CU·MF / (E·W) = 9000 × 0.4 × 0.8 / (10 × 10) = 28.8 m → take 28 m ``` With 9 m poles, S/h = 28/9 ≈ 3.1, which is acceptable for good uniformity. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. What is the waste light factor in floodlighting? A. A factor allowing for light spilling past the edges, 1.2 for regular and 1.5 for irregular surfaces B. The fraction of light absorbed by glass C. The lamp efficacy D. The ratio of floor to wall Answer: A. Some beam light misses the target; WLF increases the lumens required. (Key point: Waste light factor) 2. Which formula gives total lumens for the 40 m x 12 m front (80 lux, CU 0.5, DF 1.3, WLF 1.2)? A. E x A x CU / (DF x WLF) B. E x A x DF x WLF / CU = 119808 lm C. E x A / (DF x WLF x CU) D. E x A x CU x DF Answer: B. 80 x 480 x 1.3 x 1.2/0.5 = 119808 lm, giving 4 projectors of 32000 lm. (Key point: Floodlight total lumens) 3. For 9000 lm lanterns, CU 0.4, MF 0.8, road 10 m wide, 10 lux, what spacing results? A. 28.8 m B. 11.25 m C. 90 m D. 4.5 m Answer: A. S = F x CU x MF/(E x W) = 9000 x 0.4 x 0.8/(10 x 10) = 28.8 m. (Key point: Street lighting spacing formula) 4. How do floodlighting and street lighting differ? A. Floodlighting lights vertical surfaces/large areas with projectors; street lighting lights a long road from poles B. Both use identical formulas C. Floodlighting is indoor only D. Street lighting uses projectors only Answer: A. Floodlighting uses concentrated beams on faces or areas; street lighting lights a long horizontal road. (Key point: Floodlight vs street lighting) ## Related in Industrial Power Distribution and Illumination - [Ten factors for flood, street lighting, luminaires](https://www.bctengineer.com/question.md?key=semester_6%2Findustrial_power_distribution_and_illumination%3Aten-factors-flood-street-luminaires) — Industrial Power Distribution and Illumination, chapter 8 - [Street lighting principles and flood design](https://www.bctengineer.com/question.md?key=semester_6%2Findustrial_power_distribution_and_illumination%3Adiffusion-specular-flood-procedure) — Industrial Power Distribution and Illumination, chapter 8 - [Outdoor lighting, flood and street calculation](https://www.bctengineer.com/question.md?key=semester_6%2Findustrial_power_distribution_and_illumination%3Aoutdoor-flood-street-calculation) — Industrial Power Distribution and Illumination, chapter 8 - [Factors in power and lighting system design](https://www.bctengineer.com/question.md?key=semester_6%2Findustrial_power_distribution_and_illumination%3Apower-lighting-design-factors) — Industrial Power Distribution and Illumination, chapter 5 - [Street lighting scheme design procedure](https://www.bctengineer.com/question.md?key=semester_6%2Findustrial_power_distribution_and_illumination%3Astreet-lighting-design-procedure) — Industrial Power Distribution and Illumination, chapter 8 - [Outdoor lighting purposes and street lighting](https://www.bctengineer.com/question.md?key=semester_6%2Findustrial_power_distribution_and_illumination%3Aoutdoor-lighting-street-methods) — Industrial Power Distribution and Illumination, chapter 8, asked 2× ## Related in other subjects - [Street lighting importance and design factors](https://www.bctengineer.com/question.md?key=semester_7%2Ftransportation_engineering_ii%3Astreet-lighting-importance-design-factors) — Transportation Engineering II, chapter 1 - [At-grade intersection requirements; street lighting importance](https://www.bctengineer.com/question.md?key=semester_7%2Ftransportation_engineering_ii%3Aintersection-requirements-street-lighting-importance) — Transportation Engineering II, chapter 1 - [Accident causes and prevention; street light design](https://www.bctengineer.com/question.md?key=semester_7%2Ftransportation_engineering_ii%3Aaccident-causes-prevention-street-light-factors) — Transportation Engineering II, chapter 1 - [Tunnel lighting factors; river bank protection methods](https://www.bctengineer.com/question.md?key=semester_7%2Ftransportation_engineering_ii%3Atunnel-lighting-factors-river-bank-methods) — Transportation Engineering II, chapter 5