Fluorescent To Led Wattage Conversion

荧光灯到LED瓦数转换

Recommended Values by Application

Specification Comparison

Why Fluorescent To Led Wattage Conversion Matters

Here's the thing: a straight 1:1 wattage swap will leave you over-lit and over-paying. A 32W T8 fluorescent troffer with a magnetic ballast draws about 36W at the socket (ballast losses per IEC 60598-1). An equivalent LED panel delivering 3200 lumens at 130 lm/W needs only 24.6W. That's a 32% reduction in energy consumption — but only if you get the conversion factor right.

The catch is that fluorescent luminaires typically have lower luminaire efficacy ratings (LER) than modern LED panels. A typical 2x4 T8 troffer with a prismatic lens might achieve 60–70 lm/W system efficacy. A premium LED panel at 130 lm/W doubles that. So the conversion factor isn't just about lamp wattage — it's about system performance. I've seen projects where a 1:1 replacement left the space at 800 lux instead of the required 500 lux per EN 12464-1 for office tasks. That's wasted energy and glare issues.

What does this mean in practice? You need to calculate the target maintained illuminance, not just match the old lamp wattage. For a typical office at 500 lux maintained, a 32W T8 troffer (2 lamps) producing 5600 lumens initial with a 0.75 maintenance factor delivers about 4200 lumens. An LED panel at 130 lm/W needs 32.3W to match that — but that's still a 50% reduction from the 64W fluorescent system. Bottom line: proper conversion saves 40–60% energy while meeting EN 12464-1 illuminance targets.

Application Scenarios

Open-plan office retrofit: You've got 200 existing 2x4 T8 troffers, each with 3x32W lamps and magnetic ballasts (108W per fixture). Target maintained illuminance is 500 lux per EN 12464-1. A 2x4 LED panel at 130 lm/W delivering 4000 lumens needs 30.8W. That's a 71% reduction — from 21.6 kW to 6.16 kW for the floor. Payback at €0.12/kWh is under 18 months.

Warehouse high-bay replacement: Existing 400W metal halide (yes, not fluorescent, but common) or T5HO 54W fixtures at 8m mounting height. For T5HO, you're looking at 54W per lamp with a 0.85 ballast factor = 46W actual. An LED high-bay at 150 lm/W with a Type V distribution needs 30W to match the 4500 lumens maintained. But here's the practical aside: check the beam angle. A T5HO linear lamp spreads light differently than a round LED high-bay. You might need fewer fixtures — or more. Always run a Dialux simulation.

Retail display lighting: Track-mounted T8 28W lamps with electronic ballasts (32W actual) illuminating merchandise at 1000 lux. An LED track head at 140 lm/W with a 30° beam needs 22W to hit the same center-beam lux. But the color quality matters more here — use CRI ≥90 per CIE 097:2005 for retail. The conversion factor is 0.69, but you'll pay more for the high-CRI LED. Worth it for the color rendering.

Parking garage: T8 32W wrap fixtures with prismatic lenses at 3m mounting height. Target 75 lux maintained per IESNA RP-20-20. An LED vapor-tight at 130 lm/W with a wide distribution needs 18W. Conversion factor 0.56. The real win? No more ballast failures in cold weather — LEDs start instantly at -20°C.

Design Guidelines

Start with a photometric audit. Measure the existing maintained illuminance with a calibrated meter at task height. Don't trust the nameplate — I've seen 32W T8 fixtures that actually draw 38W because of aging ballasts. Use a power meter to confirm.

Apply this rule of thumb: for a T8 system with electronic ballasts, multiply the total fluorescent wattage by 0.50–0.60 to get the LED wattage. For magnetic ballasts, use 0.45–0.55 because the ballast losses are higher. For T5HO systems, use 0.50–0.55. These factors assume 130 lm/W LED efficacy and similar light distribution.

Always verify the luminaire layout. If you're replacing a 2x4 troffer with a 2x4 LED panel, the spacing stays the same. But if you're switching from linear fluorescent to round high-bays, recalculate the spacing using the LED's photometric file. I've seen too many retrofits where the client insisted on 1:1 replacement and ended up with dark spots between fixtures.

Check the dimming compatibility. Many LED drivers are 0-10V dimmable, but fluorescent dimming ballasts use different protocols. If you're keeping the existing dimming system, verify the driver accepts the same control signal per IEC 62386 (DALI). Otherwise, you'll need new controls.

Finally, factor in the thermal environment. LEDs are sensitive to junction temperature — a 10°C rise above 25°C can reduce L70 lifetime by 30%. In enclosed fixtures or high-ambient spaces (like a kitchen or boiler room), derate the wattage by 10–15% or choose a driver with higher temperature rating per IEC 62717.

Key Takeaways