Engineering Analysis: 70W High-Pressure Sodium to LED Commercial Retrofit
Upgrading a commercial or industrial facility from 70-watt High-Pressure Sodium 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 5,700 lm
A 70W High-Pressure Sodium lamp is rated at about 6,400 initial lumens, but averages roughly 5,700 mean lumens over its life, a 11% decline while still drawing full power. HPS holds its output better than most HID sources, so the gap is relatively small; its bigger weakness is color (CRI around 20–22). 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 5,700 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 70W High-Pressure Sodium lamp, the ballast adds about 22W (31%), so the fixture draws roughly 92W at the meter. Converting to direct-wire Type B LED hardware removes the ballast completely, cutting demand from 92W to 25–45W.
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 249.7 kWh of electricity annually, saving $32.46/year per luminaire.
- Facility-Scale Impact (25 Fixtures): Upgrading a bank of 25 fixtures cuts annual facility electricity overhead by $811.50 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.
- Faster Recovery After Outages: An HPS lamp needs roughly a minute to cool before it will restrike after a power interruption, then several minutes to reach full brightness. LEDs come back instantly at full output.
4. Primary Applications for 70W High-Pressure Sodium Retrofits
In commercial and municipal applications, 70W High-Pressure Sodium fixtures are typically deployed in residential streetlights, dusk-to-dawn yard and barn lights, small building wall packs, and entry security lights. The physical envelope corresponds to ED17 (also BD17 or ED23½) bulb with an E26 medium or E39 mogul base.
Swapping the monochromatic amber of HPS (CRI around 20–22) for an LED with CRI 70–80+ makes colors identifiable again: vehicle colors, clothing, and faces on security camera footage.
System draw drops from about 92W (lamp plus ballast) to 25–45W.
Quick Reference: 70W HPS Lamp vs. LED Replacement
| Spec | 70W HPS lamp | LED replacement |
|---|---|---|
| ANSI ballast code | S62 | None (ballast removed) |
| Bulb & base | ED17 (also BD17 or ED23½) bulb with an E26 medium or E39 mogul base | Corn bulb on the same base, or an integrated fixture |
| Light output | 6,400 initial / 5,700 mean lm | 5,700 lm target |
| Power at the meter | ~92W including ballast | 25–45W |
| Color | ~2,000–2,100K, CRI ~20–22 | 2700K–5000K, CRI 70–80+ |
| Rated life | 24,000+ hours | 50,000+ hours (L70), typical |
| Warm-up / restrike | Several minutes / about 1 minute | Instant |
What's Specific to the 70W HPS Retrofit
The medium-base trap
Many 70W HPS lamps use an ordinary-looking E26 medium base, so it is tempting to screw in a household LED bulb. Don't: the fixture still contains a ballast and an ignitor that fires starting pulses of several thousand volts, which will destroy a standard LED bulb. Use a lamp rated for direct-wire (Type B) installation and remove or bypass both the ballast and the ignitor first.
Keep the photocell
Most 70W dusk-to-dawn fixtures switch on with a built-in photocell. After a ballast bypass the photocell still works, because it simply switches line voltage to the socket. If the light cycles or stays on after the conversion, replace the photocell with one rated for LED loads.
Pick 3000K or warmer near homes
The American Medical Association's 2016 community guidance on street lighting recommends a color temperature of 3000K or lower for outdoor lighting to limit glare and blue-rich light at night. For yards, driveways, and residential streets, a 2700K–3000K LED is the closest comfortable match to the HPS glow your neighbors are used to.
Sizing From Delivered Light (Worked Example)
The 5,700 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 4,000 lm. An LED fixture producing 4,000 lm at 130 lm/W draws about 30W, versus ~92W 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 High-Pressure Sodium lamps.