Illumination engineering

Illumination engineering (or lighting design/engineering) is the science and art of providing adequate, comfortable, and efficient lighting in a space. It involves understanding how light interacts with a room, how much light people need for various tasks, and how to place luminaires (fittings) so that the space is well lit without glare, dark spots, or wasted energy.

Here’s a structured overview:

🔹 Basics of Illumination Engineering

Key Terms
- Lumen (lm): Measure of luminous flux (total light output from a source).
- Lux (lx): Illuminance = lumens per square meter. (How much light falls on a surface.)
- Watt (W): Electrical power consumed by a lamp.
- Luminous efficacy: Lumens per watt (lm/W), efficiency of a light source.
- Uniformity: Evenness of light distribution across a room.
Lighting Requirements (Lux Levels) Standards (like CIBSE, IES, or IS codes) specify recommended illuminance:
- Corridors/stairways: 100–150 lux
- Living rooms: 150–300 lux
- Kitchens/reading areas: 300–500 lux
- Offices/classrooms: 300–500 lux
- Workshops/laboratories: 500–1000 lux

🔹 Steps to Lighting Design

1. Calculate Required Lumens

$\text Required Lumens=Room Area (m²)×Illuminance Level (lux)$

Example: A 5 m × 4 m room (20 m²) used as an office, needing 300 lux:

$20×300=6000 lumens needed$

2. Account for Room Factors

Utilization Factor (UF): Fraction of light reaching the working plane (depends on fixture, room reflectance, layout).
Maintenance Factor (MF): Accounts for lamp depreciation and dirt (usually 0.8).

So:

${Total Lumens Required from Lamps} = \frac{\text{Required Lumens}}{UF \times MF}$

If UF = 0.6 and MF = 0.8:

$\frac{6000}{0.6 \times 0.8} = 12,500 \, \text{lumens}$

3. Select Number of Luminaires

If you choose LED panels with 3000 lumens each:

$\frac{12,500}{3000} \approx 4.2$

So, install 4–5 panels.

4. Placement of Fittings

Uniform Distribution: Divide the ceiling evenly; spacing between lights should be about 1–1.5 times the mounting height above the working plane.
Working Plane Height: Usually 0.8 m (desk height) in offices, floor level for circulation spaces.
Room Index (RI): Used to optimize layout.

$RI=\frac{L \times W}{H_m \times (L + W)}$

where Hm = mounting height above working plane.

General rules:
- Avoid placing lights too close to walls (<0.5 m).
- For rectangular rooms, align lights in a grid.
- In tall rooms, higher wattage or focused downlights may be needed.
- For aesthetics, combine general lighting (ambient), task lighting, and accent lighting.

🔹 Example (Practical Case)

Room: 6 m × 4 m × 3 m height (office use) Target: 300 lux Area = 24 m² → Lumens = 24 × 300 = 7200 lm With UF = 0.6, MF = 0.8 → 7200 / (0.6 × 0.8) ≈ 15,000 lm LED panels = 3000 lm each → Need 5 fixtures Placement: Arrange in a grid of 2 × 3, evenly spaced, about 1–1.5 m away from walls.

🔹 Role of Room Index (RI)

The Room Index (RI) is a geometric factor used in lighting design. It helps determine the Utilization Factor (UF) of luminaires, which tells us how efficiently the light emitted by fixtures actually illuminates the working plane.

$RI = \frac{L \times W}{H_m \times (L + W)}$

L = Room length (m)
W = Room width (m)
Hₘ = Mounting height above working plane (ceiling height − working plane height, usually desk height ≈ 0.8 m)

👉 Manufacturers provide tables where UF depends on RI and room surface reflectance. For example:

Low RI (<1): Long narrow rooms, light doesn’t distribute efficiently → UF drops.
Medium RI (1–3): Balanced rooms, good distribution → UF higher.
High RI (>3): Wide, shallow rooms, light reaches surfaces more effectively.

🔹 Step 1: Gather the values

Room length (L) = 6 m
Room width (W) = 4 m
Room height = 3 m
Fittings are mounted at 2.8 m from the floor
Working plane height (office desks) ≈ 0.8 m

So the mounting height above working plane (Hm) is:

Hm=2.8−0.8=2.0 mH_m = 2.8 - 0.8 = 2.0 \, \text{m}Hm=2.8−0.8=2.0m

🔹 Step 2: Formula for Room Index (RI)

RI=L×WHm×(L+W)RI = \frac{L \times W}{H_m \times (L + W)}RI=Hm×(L+W)L×W

🔹 Step 3: Plug in values

RI=6×42.0×(6+4)RI = \frac{6 \times 4}{2.0 \times (6 + 4)}RI=2.0×(6+4)6×4 RI=242.0×10RI = \frac{24}{2.0 \times 10}RI=2.0×1024 RI=2420=1.2RI = \frac{24}{20} = 1.2RI=2024=1.2

✅ The Room Index = 1.2

This is a relatively low RI, which means the room is somewhat long/narrow relative to the mounting height. In practice, this suggests:

Light distribution won’t be very efficient.
The Utilization Factor (UF) might be around 0.45–0.55 (depending on reflectance of walls/ceiling).
Fixtures should be arranged in a grid (2 × 2 or 2 × 3) to maintain uniformity.

Summary (for UF choices typical around RI = 1.2)

Required lumens at working plane: 7,200 lm (24 m² × 300 lx).
Adjusted lumens needed from fixtures = 7200UF×MF\dfrac{7200}{UF \times MF}UF×MF7200.

Concrete outcomes:

UF = 0.45 → Adjusted lumens ≈ 20,000 lm → 7 fittings → suggested layout 3 × 3 (9 positions, using 7).
UF = 0.50 → Adjusted lumens ≈ 18,000 lm → 6 fittings → suggested layout 3 rows × 2 cols.
UF = 0.55 → Adjusted lumens ≈ 16,364 lm → 6 fittings → suggested layout 3 × 2.
UF = 0.60 → Adjusted lumens ≈ 15,000 lm → 5 fittings → suggested layout 2 × 3.

Interpretation & recommendation

Lower UF → you need more fittings. RI = 1.2 is on the lower side, so expect UF to be lower than a very compact room; that’s why the number of fixtures can jump from 5 to 7 depending on UF.
To pick the correct UF you should consult the luminaire manufacturer’s UF tables (they list UF vs RI for different ceiling/wall reflectances). If you want, I can:
- add a manufacturer-style UF lookup table to the calculator and pick a UF based on typical reflectances (ceiling 70%, walls 50%, floor 20%),
- or re-run with a different luminaire lumen value (e.g., 2400 lm or 4000 lm) or a different target lux.
For layout: aim for a regular grid centred in the room. Keep spacing roughly 1–1.5 × Hm between fittings and about 0.5–1 × Hm from walls to avoid dark edges.

PreviousKali NetHunter Installation NextAutoCAD

Last updated 1 month ago

Was this helpful?