Engineering Analysis: 100W Metal Halide to LED Commercial Retrofit
Upgrading a commercial or industrial facility from 100-watt Metal Halide fixtures to solid-state LED systems delivers exceptional return on investment. With commercial utility rate structures, demand charges, and continuous 12-to-24 hour operational schedules, lighting retrofits frequently achieve full capital payback in under 12 to 18 months.
1. Initial vs. Mean Lumens: Why the Target Is 6,000 lm
A 100W Metal Halide lamp is rated at about 8,500 initial lumens, but averages roughly 6,000 mean lumens over its life, a 29% decline while still drawing full power. Metal halide depreciates faster than most light sources, so sizing a replacement from the initial catalog rating oversizes it. Quality LED products are rated by L70 (hours until output falls to 70% of initial), commonly 50,000 hours or more. That is why this page targets 6,000 mean lumens (real-world working light) rather than the initial rating.
2. Hidden Ballast Load
HID lamps cannot run directly on line voltage; they need a ballast (typically magnetic) to start and regulate the arc. For a 100W Metal Halide lamp, the ballast adds about 22W (22%), so the fixture draws roughly 122W at the meter. Converting to direct-wire Type B LED hardware removes the ballast completely, cutting demand from 122W to 35–50W.
3. Commercial Facility Savings & Demand Charge Reductions
Operating on an industrial duty cycle of 12 hours per day, 365 days per year:
- Single Fixture Energy Reduction: Upgrading one socket eliminates 348.2 kWh of electricity annually, saving $45.27/year per luminaire.
- Facility-Scale Impact (25 Fixtures): Upgrading a bank of 25 fixtures cuts annual facility electricity overhead by $1131.75 every year.
- Zero Re-Lamping Maintenance: High-bay, canopy, and pole fixtures require bucket truck or scissor lift rentals costing $500–$1,200 per service call. With a 50,000-to-100,000 hour commercial lifespan, LED upgrades eliminate recurring maintenance cycles for 10+ years.
- Instant Full Restrike: Metal halide lamps need roughly 10 to 15 minutes to cool and restrike after a power interruption. LEDs restrike instantly at 100% brightness, eliminating dark downtime and safety hazards in industrial plants.
4. Primary Applications for 100W Metal Halide Retrofits
In commercial and municipal applications, 100W Metal Halide fixtures are typically deployed in small building wall packs, gas station and drive-through canopies, and auto dealership display lighting. The physical envelope corresponds to ED17 bulb with an E26 medium base (some fixtures use ED28 with an E39 mogul base).
A 100W MH lamp starts at about 8,500 lumens and averages about 6,000 over its life. A 35–50W LED delivers that working light level without the gradual dimming.
System draw with the ballast is about 122W; the LED replacement draws 35–50W in total.
Quick Reference: 100W Metal Halide Lamp vs. LED Replacement
| Spec | 100W Metal Halide lamp | LED replacement |
|---|---|---|
| ANSI ballast code | Pulse-start (read the M-code on the ballast label) | None (ballast removed) |
| Bulb & base | ED17 bulb with an E26 medium base (some fixtures use ED28 with an E39 mogul base) | Corn bulb on the same base, or an integrated fixture |
| Light output | 8,500 initial / 6,000 mean lm | 6,000 lm target |
| Power at the meter | ~122W including ballast | 35–50W |
| Color | ~3,700–4,200K, CRI ~65–70 (ceramic MH: 80–90+) | 3000K–5000K, CRI 80–90+ |
| Rated life | 10,000–15,000 hours, varies by lamp | 50,000+ hours (L70), typical |
| Warm-up / restrike | 2–5 minutes / about 10–15 minutes | Instant |
What's Specific to the 100W Metal Halide Retrofit
Match 4000K to keep the familiar look
Standard metal halide renders at roughly 3,700–4,200K. A 4000K LED keeps the same crisp white look your customers are used to; a 5000K LED will look noticeably bluer next to any metal halide fixtures you have not converted yet.
Motion sensors finally make sense
Metal halide cannot be cycled with a motion sensor because it needs minutes to warm up and much longer to restrike. LED wall packs and canopy lights can run at low output overnight and jump to full brightness instantly when a car or person arrives.
Full-cutoff wall packs reduce glare
Many older 100W wall packs are "forward throw" designs that shine into drivers' eyes and onto neighboring property. If you replace the whole fixture, a full-cutoff LED wall pack aims the light down where it is useful.
Sizing From Delivered Light (Worked Example)
The 6,000 lm target above is a lamp-for-lamp match, which is the safe choice for a screw-in corn bulb. If you are replacing the whole fixture, you can often target fewer lumens. HID lamp ratings describe the bare lamp, and part of that light is lost inside the housing and reflector, while LED fixture ratings are measured for the complete fixture (IES LM-79 absolute photometry).
Example: if your existing fixture is 70% efficient, it delivers about 4,200 lm. An LED fixture producing 4,200 lm at 130 lm/W draws about 30W, versus ~122W today. Treat this as an estimate; the fixture maker's photometric report or a lighting layout is the authoritative answer.
5. Commercial Installation: Type B Ballast-Bypass Protocol
For maximum electrical efficiency and long-term reliability, a Type B (ballast-bypass) conversion is standard engineering practice:
- Disconnect Power: Lock out and tag out the circuit breaker supplying the lighting circuit.
- Bypass the Ballast: Disconnect the incoming line voltage (120–277V) and neutral wires from the legacy magnetic or electronic ballast. Cut or remove the ballast entirely, along with the ignitor and capacitor if the fixture has them (an ignitor left in the circuit sends high-voltage pulses that can destroy an LED driver).
- Wire Directly to Sockets: Connect line voltage directly to the socket leads according to the manufacturer's installation diagram.
- Label the Fixture: Affix the provided warning label inside the fixture housing indicating that the fixture has been modified to run line voltage and will no longer accept legacy Metal Halide lamps.