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
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 around €250 per year at current ESB rates. Payback in under 6 months.
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.
Room Index k
The Room Index (also called Room Cavity Ratio in IESNA) describes the shape of a room relative to its mounting height. A higher k means a more efficient room shape.
Utilisation Factor (UF) table
UF values below are generic for a standard GU10 recessed downlight with assumed room reflectance of ceiling 70%, walls 50%, floor 20% — typical Irish painted plaster finish.
| 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 (available from Philips, Aurora, Osram, Megaman, etc.).
Maintenance Factor (MF)
MF accounts for lumen depreciation over time and dust accumulation. This tool uses MF = 0.80, appropriate for:
- Modern LED source with L70 rating (70% lumen maintenance at rated life)
- Clean indoor residential environment
- Regular lamp replacement / cleaning schedule
CIBSE LG09 range: 0.70 (dirty/rarely cleaned) to 0.85 (very clean/frequent maintenance).
Target illuminance values
Values are adapted from EN 12464-1:2021 (work environments) and CIBSE / SLL recommendations for residential applications:
| Room | Lux (this tool) | Source / basis |
|---|---|---|
| Living Room | 150 | CIBSE residential best practice |
| Kitchen (ambient) | 300 | CIBSE / SLL residential guide |
| Kitchen (task) | 500 | EN 12464-1 §5.3 food prep areas |
| Bedroom | 100 | CIBSE residential best practice |
| Bathroom | 200 | CIBSE / SLL residential guide |
| Home Office | 500 | EN 12464-1 §5.2 office tasks |
| Hallway | 100 | CIBSE residential best practice |
Note: EN 12464-1 is a work-environment standard. Residential lux values follow established CIBSE / SLL guidance rather than a statutory requirement.
Spacing rule
Maximum centre-to-centre spacing is limited by the CIBSE Spacing-to-Height Ratio (SHR):
Where Hm is the mounting height above the work plane. SHR = 1.5 is a conservative value typical for standard GU10 downlights. Precise SHR values are published in manufacturer polar curve / photometric data.
Energy & CO₂ (Savings tab)
| Factor | Value | Source |
|---|---|---|
| Electricity rate | €0.43/kWh | CRU avg residential tariff, April 2026 |
| CO₂ factor | 0.295 kg/kWh | SEAI Grid Emission Factor 2023 |
Referenced standards & sources
Find this useful?
Share the Irish Lighting Calculator
Help your friends, neighbours, or clients plan their lighting properly.
Free tool, no sign-up, built for Irish homes.
Calculations follow EN 12464-1 lighting standards · Free tool by Lighting Dublin