Professional Lighting Calculator
Designed for Irish homes. Get accurate lumens, downlight counts and LED savings — calibrated for 2.4 m ceilings and Irish electricity rates.
Choose your room
Room dimensions
Lighting mood user adjustment
Mirror lighting
Standard 2.4 m Irish ceiling assumed. Results are practical estimates — perfect for planning your lighting layout before calling an electrician.
Your Results
Select your room and enter dimensions to see your tailored Irish lighting plan.
Use warm 2700K dimmable LEDs for that classic Irish cosy glow.
Switching 10 halogen GU10s to LEDs saves the average Irish home €300+ per year at current rates — the bulbs typically repay themselves in under 3 months.
Over a table, the shade bottom should sit at least 30 cm above seated eye level (~130 cm from floor) so it never blocks the view across the table.
Match the Kelvin across every fitting in the same visual zone — 2700K over a dining table reads far more inviting than 4000K.
Quick Lumens Estimator
A fast alternative calculator that factors in wall colour, ceiling height, and natural daylight. Perfect for a quick check before using the detailed lumen method above.
Methodology & Sources
Calculation method
This tool uses the lumen method — the standard photometric design approach used by lighting engineers across Ireland, the UK and Europe.
Work plane & Room Index k
This tool uses a work plane height of 0.75 m (CIBSE residential standard).
Mood multipliers — user adjustment (non-normative)
| Mood | Multiplier | Effect | Normative? |
|---|---|---|---|
| Cosy Warm | ×0.8 | Below CIBSE minimum — decorative/relaxation only | No |
| Standard | ×1.0 | CIBSE base lux — code-compliant result | Yes ✓ |
| Bright | ×1.3 | Above CIBSE minimum — well-lit, high-clarity | No |
| Task | ×1.6 | High-demand task areas, supplementary lighting | No |
Pendant & suspension sizing rules
The Pendant Sizing tab applies standard residential practice, adapted for 2.4 m Irish ceilings:
| Scenario | Diameter | Hanging height |
|---|---|---|
| Over a dining table | ½ to ⅔ of table width (room rule cap) | 70–80 cm above the table surface |
| Over a kitchen island | 25–35 cm per pendant; 2 up to 2.4 m, 3 beyond | 75–85 cm above the counter |
| Open floor space | Ø (cm) ≈ (L + W in feet) × 2.54 | Shade bottom ≥ 200 cm from the floor |
| Any scenario | Scale up 5–10% for ceilings over 2.8 m | ≥ 30 cm above seated eye level over tables |
⚠️ These are proportion rules of thumb — the room's furniture and sightlines should guide the final choice. Downlight spacing in the lumen method tool also respects the CIBSE ≤ 1.5 × Hm maximum-spacing rule.
Utilisation Factor (UF) table
| Room Index k | UF (used) | CIBSE typical range |
|---|---|---|
| < 0.75 | 0.42 | 0.38–0.46 |
| 0.75 – 1.0 | 0.50 | 0.46–0.54 |
| 1.0 – 1.5 | 0.57 | 0.53–0.61 |
| 1.5 – 2.0 | 0.62 | 0.58–0.66 |
| 2.0 – 3.0 | 0.68 | 0.64–0.72 |
| > 3.0 | 0.72 | 0.69–0.75 |
⚠️ For precise calculations, use the UF table from your specific luminaire's photometric datasheet.
Target illuminance values
| Room | Lux (this tool) | Source / basis |
|---|---|---|
| Living Room | 150 | CIBSE residential best practice |
| Kitchen (ambient) | 300 | CIBSE / SLL residential guide |
| Bedroom | 100 | CIBSE residential best practice |
| Bathroom (ambient) | 200 | CIBSE / SLL residential guide |
| Bathroom (mirror task) | +600 lm | CIBSE: 500 lux at face height |
| Home Office | 500 | EN 12464-1 §5.2 office tasks |
| Dining Room | 150 | CIBSE residential best practice |
| Hallway | 100 | CIBSE residential best practice |
| Utility / Garage | 300 | Task-oriented residential / storage |
Referenced standards & sources
Recommended Lux Levels for Irish Homes
Different rooms require different lighting levels. The values below are based on EN 12464-1:2021 and CIBSE residential guidance, adapted for standard Irish ceiling heights of 2.4m.
| Room | Lux (ambient) | Typical use | Colour temp |
|---|---|---|---|
| Living Room | 150–300 | General relaxation and entertainment | 2700K |
| Kitchen | 300–500 | Food preparation and cooking | 3000–4000K |
| Bedroom | 100–200 | Rest and ambient lighting | 2700K |
| Bathroom | 200–400 | Grooming and hygiene tasks | 3000K |
| Home Office | 300–500 | Reading and computer work | 4000K |
| Dining Room | 150–300 | Meals and socialising | 2700K |
| Hallway | 100–150 | Navigation and circulation | 2700–3000K |
| Utility / Garage | 300–500 | Tasks, laundry and storage | 4000K |
Sources: I.S. EN 12464-1:2021 · CIBSE Code for Lighting 2022 · CIBSE LG09 Residential guidance.
How Many Lumens Do You Need Per Room?
Lumens measure the total light output of a fitting. Here are lumen-method estimates (UF 0.57 · MF 0.80) for typical Irish room sizes, based on standard ceiling heights of 2.4m — add lamps to layer the light in living spaces.
Living Room ~20 m²
At CIBSE 150 lux, a 20 m² sitting room needs about 6,600 source lumens from the ceiling — then add floor and table lamps to layer the light.
Kitchen ~12 m²
Plan for 300 lux ambient overhead (≈ 7,900 lm), plus 500 lux over worktops via under-cabinet LED strips or targeted downlights.
Bedroom ~15 m²
Bedrooms benefit from lower ambient light (100 lux ≈ 3,300 lm) with separate task lighting at bedside level.
Bathroom ~6 m²
Use IP65-rated fittings above the shower. Mirror lighting should provide 500 lux at face height.
Home Office ~10 m²
EN 12464-1 recommends 500 lux for sustained desk work. Invest in quality 4000K lighting to reduce eye strain.
Hallway ~8 m²
Space downlights every 1.2–1.5m along the run. Two fittings are more effective than one central point for halls over 4m.
LED Efficiency Comparison
Lumens per watt (lm/W) measures how efficiently a light source converts electricity into visible light. Modern LED technology is 6–10× more efficient than traditional incandescent bulbs.
For an Irish home running lights 5–6 hours per day, switching from halogen to LED typically saves €300+ per year at current rates (38.04c/kWh inc. VAT, Electric Ireland standard, Aug 2026 — effective all-in cost ~43–44.5c/kWh once standing charges are included).
Browse LED Bulbs →| Technology | Lumens per Watt | Lifespan | Efficiency |
|---|---|---|---|
| LED | 80–120 lm/W | 15,000–25,000h | |
| CFL | 45–75 lm/W | 6,000–15,000h | |
| Halogen | 15–25 lm/W | 1,000–4,000h | |
| Incandescent | 10–15 lm/W | 750–1,500h |
Source: SEAI — Sustainable Energy Authority of Ireland · EU Ecodesign Regulation 2019/2020
Lighting Calculator — Frequently Asked Questions
General lighting
What is a lumen?
A lumen (lm) measures the total amount of visible light emitted by a light source. A standard 60W incandescent bulb produces around 800 lumens. A modern 8W LED produces the same 800 lumens while using 87% less electricity.
What is lux?
Lux (lx) measures illuminance — the amount of light falling on a surface per square metre. One lux equals one lumen per square metre (1 lx = 1 lm/m²).
What is the difference between lux and lumens?
Lumens measure total light output from a source. Lux measures how much of that light reaches a surface. For room lighting calculations, lux is the useful measurement.
How do I calculate lighting requirements for a room?
The standard method is the lumen method: Total lumens = (Lux × Area) ÷ (UF × MF). This calculator does that automatically using EN 12464-1 values.
Room-specific
How many lumens do I need for a living room?
Using the lumen method (UF 0.57, MF 0.80), a typical Irish living room of 20 m² needs about 6,600 source lumens for 150 lux ambient — for example 12× 550 lm downlights, or a 4,000 lm pendant plus 6 downlights. Add 2,000–3,000 lm in floor and table lamps for reading and task pockets. Use the calculator above with your exact dimensions.
How many lumens do I need for a kitchen?
A kitchen of 12 m² needs about 7,900 lumens for 300 lux ambient overhead, plus under-cabinet LED strips delivering 500 lux directly on the worktops.
How many lumens do I need for a bedroom?
A bedroom of 15 m² needs about 3,300 lumens for 100 lux ambient (roughly 6× 550 lm downlights or one dimmable ceiling fitting), plus around 400 lm per bedside for reading. Dimmable fittings give the most flexibility.
How many downlights do I need?
Divide the total source lumens required by the output of each downlight. A 20 m² living room needing 6,600 lumens (150 lux, lumen method) requires approximately 12× 550 lm GU10 LEDs — or fewer, higher-output fittings if you prefer.
What size pendant do I need over a dining table?
As a rule, the pendant diameter should be ½ to ⅔ of the table width — or use the room rule: length + width in feet = ideal diameter in inches. Hang it 70–80 cm above the table surface. The Pendant Sizing tab above works it out for your exact room.
How many pendants should hang over a kitchen island?
Two pendants for islands up to about 2.4 m, three for longer islands — each 25–35 cm wide, evenly spaced, hanging 75–85 cm above the counter.
Technical
What is Maintenance Factor (MF)?
Maintenance Factor (MF) accounts for the gradual reduction in light output over time. This calculator uses MF = 0.80, appropriate for modern LED sources in a clean residential environment.
What is Utilisation Factor (UF)?
Utilisation Factor (UF) describes what proportion of the light produced by a fitting actually reaches the work plane. This calculator uses generic UF values for standard GU10 downlights with typical Irish reflectances: ceiling 70%, walls 50%, floor 20%.
What lighting standard does this calculator use?
This calculator uses the lumen method as defined in EN 12464-1:2021 (I.S. EN 12464-1, published by NSAI) and the CIBSE Code for Lighting 2022. Work plane height is 0.75 m (CIBSE residential standard).
Can I use this calculator for commercial projects?
This tool is designed for residential use and provides indicative values only. For commercial projects, use luminaire-specific photometric data and consult a qualified lighting designer.
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Calculations follow EN 12464-1 lighting standards · Free tool by Lighting Dublin
