LED luminaires use 50–70% less energy than the fluorescent fittings they replace, last three to five times longer, and eliminate mercury-containing lamps. This guide covers the technical differences, replacement options, dimming controls, power factor, and the regulations that apply to commercial LED projects.
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Written and reviewed by Andrew Moore, founder of Elec-Mate, against BS 7671:2018+A4:2026, IET Guidance Note 3 and the IET On-Site Guide.
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Commercial fluorescent lighting — T8 and T5 tubes, high-bay metal halide, and compact fluorescent — is being rapidly replaced by LED. The energy savings are substantial: LED luminaires typically use 50–70% less energy than the fluorescent fittings they replace, and their lifespan is three to five times longer.
For UK electricians, commercial LED retrofit projects are a significant and growing revenue stream. However, they require an understanding of the technical differences between LED and fluorescent technologies — particularly regarding driver compatibility, power factor, dimming controls, and the disposal of mercury-containing fluorescent lamps. This guide covers everything needed to design, install, and certify a commercial LED upgrade under BS 7671:2018+A4:2026.
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The efficiency of a light source is measured in lumens per watt (lm/W) — how much visible light output is produced per watt of electrical input. Higher is better.
| Light Source | Typical Efficacy | Power (per fitting) |
|---|---|---|
| T8 Fluorescent (inc. ballast) | 55–75 lm/W | 58W (36W tube + losses) |
| T5 Fluorescent (HF ballast) | 85–100 lm/W | 28–35W |
| Metal Halide High-Bay | 70–100 lm/W | 400W |
| LED Linear (T8 replacement) | 100–160 lm/W | 15–22W |
| LED High-Bay | 120–180 lm/W | 100–200W |
The energy saving from T8 fluorescent to LED linear is typically 60–70% per fitting. At 25p/kWh commercial electricity rate and 4,000 operating hours per year, a 38W saving per fitting equates to £38 per fitting per year in electricity savings.
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The L70 rating of an LED luminaire indicates the hours at which the lumen output has degraded to 70% of the initial value. At 50,000 hours (L70), the luminaire is still producing 70% of its original light output — still adequate for most applications. Specify LED luminaires with L70 >50,000 hours for commercial applications.
LED luminaires offer superior dimming performance compared to fluorescent. Fluorescent dimming requires high-frequency dimmable ballasts (DALI or 1-10V/0-10V) and typically cannot dim below 10% without instability. LED can dim smoothly to 1% or below with compatible drivers.
LED drivers are switching power supplies that can introduce power factor issues and harmonic distortion into the supply network. For commercial installations:
Commercial LED Specification Requirements
Use the Elec-Mate cable sizing calculator with the actual VA load (apparent power, including the effect of power factor) when sizing cable for commercial LED lighting circuits. A 2,000W LED installation with PF 0.9 draws 2,222VA — size the cable for 2,222VA, not 2,000W.
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Start free trialReplace fluorescent tube only. Existing ballast remains. Quick installation, minimal labour. Risk: ballast compatibility must be verified. Ballast still consumes power and will eventually fail.
Ballast is bypassed; LED tube wired directly to mains. Eliminates ballast losses and compatibility issues. Requires rewiring of the fitting. Best long-term reliability. Must label fitting as mains voltage.
Replace the entire fitting with a new LED luminaire. Higher capital cost but best performance, controls compatibility, and warranty. Recommended for large commercial projects and installations with DALI or BMS control.
Commercial LED lighting installations must comply with several regulations and standards:
Commercial LED retrofit projects typically range from £5,000 (small office) to £200,000+ (large warehouse or factory). Electricians who can design, supply, install, and certify LED upgrades — including energy savings calculations, proper power factor analysis, and WEEE disposal — can command premium margins over those who only install.
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