Lighting Design

Part of Lighting

Planning illumination systems for homes, workshops, and community spaces.

Why This Matters

Lighting design is the process of planning where to put lights, how bright to make them, and how to control them to achieve both adequate illumination and minimum power consumption. Done well, a thoughtfully designed lighting system using 30 watts provides better practical illumination than a haphazard one using 100 watts. In a rebuilding community with limited electrical capacity, this difference matters enormously.

Bad lighting design creates hazards. Poor placement leaves critical work surfaces in shadow. Single-point illumination creates deep shadows under tools and hands — exactly where you need to see. Over-bright spaces waste battery charge that could run a water pump or power a radio. Under-lit corridors cause falls and injuries.

Good lighting design requires understanding three things: how much light different tasks need, how light behaves in spaces (spread, reflection, shadows), and how to combine sources to create even, efficient illumination. None of this requires advanced mathematics — it requires spatial thinking and methodical planning.

Planning a Lighting Layout

Step 1: Inventory Spaces and Tasks

Before placing any light, catalog every space in a building and its primary activities:

• Living areas: conversation, eating, reading
• Sleeping areas: rest, minimal navigation
• Kitchen/cooking: food preparation, fire management
• Workshop: tool use, measurement, fabrication
• Storage: finding and retrieving items
• Corridors/stairs: safe passage

Each category has a target illuminance (see Light Levels). Write down the target for each space before proceeding.

Step 2: Note Room Dimensions and Reflectances

Measure room dimensions. Note ceiling height — this determines the minimum spread from ceiling-mounted fixtures. Record wall and ceiling colors:

• White painted surfaces: 70–80% reflectance
• Light grey or cream: 50–60% reflectance
• Medium colors (pale yellow, pale blue): 40–50% reflectance
• Dark colors, bare wood: 15–30% reflectance
• Raw stone or bare earth: 10–20% reflectance

High reflectance multiplies your light efficiency. In a room with dark stone walls, you may need three times the lumens to achieve the same perceived brightness as a white-painted room.

Step 3: Determine Fixture Locations

Ceiling-mounted general lights: Place at the geometric center of zones you want to illuminate evenly. For large rooms, use multiple fixtures rather than one powerful central fixture. One bright central light creates bright-center/dark-corner contrast; two or four distributed lights give even illumination.

Wall-mounted lights: Useful for corridors and stairways. Place at head height (1.6–1.8m) aiming slightly downward. Light the floor surface, not the wall.

Task lights: Position to illuminate the work surface without the worker’s body casting shadows on it. For a right-handed person at a bench, the task light should come from the left front — light comes over the left shoulder, away from the dominant hand.

Rule of thumb for spacing ceiling fixtures: To achieve good uniformity, maximum spacing between fixtures should not exceed 1.5 times the mounting height above the work plane. For a 2.4m ceiling with lights 0.8m above a 0.8m bench (effective height 1.6m), space fixtures no more than 2.4m apart.

Step 4: Calculate Wattage Needed

Using the lumen method:

Total lumens needed = Target lux × Area (m²) / Room efficiency factor

Room efficiency factor:
  High-reflectance white room, good fixture efficiency: 0.65–0.75
  Medium reflectance, typical room: 0.45–0.55
  Dark walls, poor fixture efficiency: 0.25–0.35

Then divide by your LED efficiency (lumens per watt) to get required wattage.

Example — 6m × 4m kitchen, target 300 lux, medium reflectance:

Lumens needed = 300 × 24 / 0.50 = 14,400 lumens
At 100 lm/W LED: 144W total
This seems high — use task lighting to reduce general level to 150 lux:
  General: 150 × 24 / 0.50 = 7,200 lm → 72W (four 18W panels)
  Task at counters: 3 × 5W strips = 15W → 500 lux at the counter
  Total: 87W for a fully functional kitchen lighting system

Specific Room Designs

Workshop Lighting

Workshops require the most demanding lighting — high levels, good uniformity, no deep shadows around machine tools.

Key principles:

1. Multiple overhead sources — at least four fixtures in a 5m × 5m shop, one per quadrant
2. No fixture directly above a rotating machine — this creates stroboscopic illusion that makes blades appear stationary (dangerous)
3. Dedicated task lights at every fixed workstation — band saw, lathe, drill press, workbench each need their own directed light
4. No shadows at critical measurement points — a machinist measuring with calipers needs shadow-free illumination from multiple angles

Recommended workshop layout (5m × 5m):

• Four 10W LED panels flush-mounted to ceiling, one in each 2.5m quadrant (40W, ~4,000 lm)
• Two 5W adjustable LED arms at primary workbenches (10W, ~900 lm directed at bench)
• One 5W under-cabinet LED strip at bench for close measurement work
• Total: 55W, approximately 5,000 useful lumens reaching work surfaces

Medical/First Aid Area

Color rendering quality matters here more than anywhere else. Incorrect skin color assessment can lead to diagnostic errors.

Requirements:

• Minimum 500 lux at examination surface, 1,000+ for wound care
• High CRI (90+) warm-white LEDs preferred
• Shadow-free illumination from multiple angles for wound inspection
• Portable battery-backed lamp for use in any location

Simple exam light: Four 5W warm-white LEDs (CRI 90+) mounted in a reflector hood, wired in series-parallel for 12V. Bolt to an adjustable arm over the examination table. Supplement with a handheld battery flashlight for deep-cavity examination.

Sleeping Areas

Minimize light in sleeping areas. Bright light disrupts circadian rhythms and degrades sleep quality.

Requirements:

• Dim navigational light (under 10 lux) sufficient to find the door without waking others
• Switch at entry AND at each sleeping position (so occupants can turn out the light without crossing the room)
• No blue-spectrum (cool white) sources — blue light suppresses melatonin. Use warm-white LEDs at 2,700–3,000K or amber-tinted sources

Implementation: A single 0.5W warm-white LED near the floor provides adequate navigation light. Add a 3W warm-white bedside reading light for those who need it, switchable independently.

Communal Dining/Meeting Spaces

These spaces benefit from dimming capability — bright during work, dim and warm during meals.

Design strategy:

• Install a general level at 200 lux for work
• Use warm-white sources throughout
• Add a lower-power warm circuit (dim amber or very low lux) for evenings
• Two separate switches allow choosing between work level and social level

If dimming hardware is unavailable, two separate circuits at different light levels achieves the same result.

Emergency and Fallback Lighting

Every lighting design must account for power failures. Plan a minimum safety layer that operates independently.

Emergency requirements:

• Every exit clearly visible from any point in the building
• Stairs and step changes illuminated
• Critical hazards (open pits, sharp equipment, fire areas) marked

Implementation options:

1. Battery-backed LED emergency lights: Salvaged exit signs and emergency fixtures contain their own sealed lead-acid batteries that self-charge when main power is present and switch automatically on outage. Collect and maintain these.
2. Strategic oil lamps: One functional oil lamp at each emergency location (near stairs, at exits). Fuel them and test them monthly.
3. Glow-in-dark paint or tape: Applied to stair edges, door handles, and exit paths. No power required. Recharges from any light source.
4. Dedicated emergency battery circuit: A small sealed battery, kept fully charged by a trickle from the main system, powers a few critical LEDs. Relay disconnects main charging and connects emergency load on power failure.

Controls and Switching

Efficient use of any lighting system requires convenient controls. If lights cannot be turned off easily, they will run unnecessarily.

Basic rule: Every light should have a switch within arm’s reach of the natural entry point to the space it illuminates.

Multiple-location switching: A corridor, stairway, or large room should have switches at both ends. Wire as three-way (two-switch) circuits — see Switch Wiring.

Circuit grouping: Group lights by zone and task level on separate circuits. Allows turning off areas not in use without affecting others. In a home: bedroom circuit, kitchen/work circuit, living area circuit, outdoor circuit — all independently controlled.

Timers: Simple mechanical timers on outdoor security lights prevent them running all night when only early-evening coverage is needed. A 120-minute timer on the workshop saves power on nights when work runs short.