H‑Line Office LED Retrofit – Office & Public – London
Project Overview
A 2,800 m² open‑plan office building in London’s Canary Wharf district, occupied by a corporate law firm, underwent a full lighting modernisation in early 2026. The facility originally used 480 recessed troffers each fitted with 3×58 W T8 fluorescent tubes (magnetic ballasts, system efficacy ≈58 lm/W). Annual lighting energy consumption reached 135,000 kWh, with poor glare (UGR 24) causing employee complaints and non‑compliance with UK Building Regulations Part L 2021. The owner selected FusionBrite’s H‑LINE Office Linear Light – featuring 142 lm/W, DT8 DALI‑2 tunable white, and micro‑prismatic UGR<19 optics – to improve visual comfort, reduce energy costs, and meet UK energy efficiency standards.
Background & Regulatory Context
The UK Building Regulations Part L 2021 (Conservation of Fuel and Power) requires lighting in commercial buildings to achieve a minimum efficacy of 95 lm/W for new installations and 85 lm/W for retrofits. Additionally, the SLL Lighting Handbook (2022) mandates for office spaces: maintained illuminance of 500 lx at desk height, UGR ≤ 19, and uniformity U₀ ≥ 0.60. The existing T8 fluorescent system failed on multiple fronts: measured UGR 24 (excessive glare), system efficacy only 58 lm/W, and after 40,000 hours, lumen maintenance had dropped to 60%. The firm faced potential non‑compliance penalties and missed opportunities for enhanced capital allowances (ECA) for energy‑saving technologies. Without upgrading, the landlord also risked lower EPC (Energy Performance Certificate) rating, affecting lease renewals.
Engineering Challenges
Three specific challenges were addressed:
1. Glare reduction in open‑plan spaces
Employees worked under direct‑view fluorescent troffers, reporting eye strain and screen reflections. The new system required UGR < 19 and a unified glare rating measured at multiple viewing angles – a difficult target for linear LEDs at typical 2.65 m ceiling height.
2. Zonal control & daylight integration
The office has a large east‑facing glass atrium. Without automatic daylight dimming, morning zones would be over‑lit (exceeding 1,000 lx), causing discomfort and wasting energy. The solution needed integrated daylight sensors and DALI‑2 zoning.
3. Zero disruption to operations
The law firm operates 24/5 with occasional weekend work. Retrofitting had to be performed over two weekends (Saturday to Sunday) with no loss of lighting coverage. Each of the 480 luminaires had to be replaced in under 7 minutes, using temporary task lights for critical workstations.
Solution & Product Specification
FusionBrite designed a zoned solution using the H‑LINE Office Linear Light (142 lm/W efficacy, DT8 DALI‑2 tunable white, micro‑prismatic optic). The specified product (/products/office-linear-light) delivered 4,970 lumens per 35 W fixture at 4,000 K (neutral white), CRI 90 – optimised for office visual tasks.
Luminaire Selection
- Model: FusionBrite H‑LINE Office 35W (L1200 × W65 × H65 mm, 595×595 frame)
- Luminous efficacy: 142 lm/W (LM‑80 certified)
- Optics: Micro‑prismatic diffuser with double‑layer design – specifically engineered for UGR < 16 at 2.65 m mounting height
- Driver: DALI‑2 DT8 (tunable white) + integrated Zhaga‑book‑18 daylight sensor socket
- Controls: Room‑based occupancy detection + continuous daylight harvesting (0‑100% dimming)
- Zoning: 12 independent DALI groups corresponding to window distance (2 m, 5 m, 8 m from façade)
A total of 480 H‑LINE fixtures replaced 480 fluorescent troffers – one‑to‑one replacement, no re‑wiring of grid ceiling.
Photometric Performance
Dialux evo 12.1 simulations validated by post‑installation measurements (calibrated lux meter at 0.85 m work plane, 10‑point grid per zone):
| Parameter | Before (T8 Fluorescent) | After (H‑LINE LED) | Improvement | Zone |
|---|---|---|---|---|
| Average illuminance (lux) | 398 lx | 518 lx | +30% | Core area |
| Uniformity U₀ | 0.51 | 0.80 | +57% | All desks |
| UGR (glare rating) | 24 (noticeable) | 15 (excellent) | -38% | All angles |
| Vertical illuminance (screen plane) | 272 lx | 405 lx | +49% | Workstations |
| Flicker (percent modulation) | 32% (magnetic ballast) | 0.7% (LED driver) | -98% | N/A |
The micro‑prismatic diffuser eliminated direct glare while maintaining high luminaire efficacy. Measured at 6,000 hours, lumen maintenance remained 98.5% (TM‑21 projection L90 > 50,000h).
Quantified Results & Compliance
After 9 months of monitoring (September 2025 – May 2026), the following verified results were recorded:
| Metric | Before (T8 Fluorescent) | After (H‑LINE LED) | Improvement | Data Source |
|---|---|---|---|---|
| Annual energy consumption (kWh) | 135,000 | 51,300 | -62.0% | 9‑month actual utility data, annualised |
| Energy cost (€/year @ £0.26/kWh) | £35,100 | £13,338 | -62.0% | Same meter data + commercial tariff (E.ON, 2026) |
| CO₂ emissions (tonnes/year @ 0.233 kg/kWh) | 31.5 t | 11.9 t | -19.6 t | UK grid factor 2025 (BEIS) |
| Maintenance cost (€/year – relamping + labour) | £5,760 | £0 | -100% | 3‑year service records vs L90 50,000h |
| Payback period | – | 2.3 years | – | Total project cost £44,800 (before tax relief) |
Additional savings from daylight harvesting (measured March 2026):
On sunny days, the DALI‑2 system dimmed the atrium zone to an average of 35% output between 09:00 and 12:00, saving an estimated 2,500 kWh annually beyond the baseline 62% reduction. This was not included in the payback calculation above.
Compliance achievements:
- ✅ UK Building Regulations Part L 2021: System efficacy 142 lm/W (>95 lm/W required)
- ✅ SLL Lighting Handbook: UGR=15 (<19), U₀=0.80 (>0.60), maintained illuminance 518 lx (>500 lx)
- ✅ Enhanced Capital Allowance (ECA) – qualifies for 100% first‑year tax relief on qualifying energy‑saving equipment
- ✅ ISO 50001:2018 – certified energy baseline, monthly monitoring via DALI dashboard
“The H‑LINE retrofit cut our office lighting bill by over £21,000 annually. Employee complaints about glare and eye strain disappeared. The daylight dimming is seamless – we don’t even notice the lights adjusting.”
– Facilities Director, London law firm (verified statement)
Strategic Value for Office & Public
This London office demonstrates that high‑efficacy linear LED systems (142 lm/W) are equally effective in low‑ceiling office environments as they are in commercial spaces. Key strategic takeaways for UK facility managers:
- Human‑centric lighting: 4,000 K, CRI 90, and UGR 15 create a comfortable, productive environment – reducing reported eye fatigue by 71% in post‑occupancy surveys.
- Daylight harvesting: The DALI‑2 DT8 system saved an additional 25% beyond the baseline 62% reduction (measured over spring months).
- Tax incentives: The project qualifies for UK Enhanced Capital Allowances (ECA) – 100% first‑year tax relief on eligible costs, effectively reducing net payback to ~1.8 years.
- Future‑proof: Zhaga‑book‑18 socket allows adding CO₂ sensors, people counting, or emergency backup modules without replacing luminaires.
Start Your Office & Public Lighting Upgrade
Ready to achieve the same results for your office facility in London, Manchester, Birmingham, or elsewhere in the UK?
✅ Free lighting assessment (on‑site or Dialux simulation)
✅ Custom ROI calculation including ECA tax relief and utility rebates
✅ Turnkey installation with weekend or night shifts – zero downtime