MDN Electricand General Repair

residential · Prince George, BC

One Dead Fixture, One Still Burning — Replace One or Both? Here's the Math

By Matt Neuls, Red Seal electrician · 2026-07-21

The call usually comes in the same way: a building with a pair of HPS dusk-to-dawn fixtures — one on each end, same age, same lamps — and one of them has gone dark. The owner wants the dead one dealt with. The other one still lights, so the instinct is to leave it alone.

That instinct feels thrifty. Run the numbers, though, and "just fix the broken one" turns out to be the expensive option — by about $236 over the next decade. Here's the math.

What a service visit actually costs

Before a single fixture goes on the wall, a visit carries fixed costs: a $135 service visit and a $15 electrical permit. That's $150 whether one fixture gets replaced or two. The visit fee mostly covers travel, setup, and making the circuit safe to work on — once that circuit is open, hanging a second fixture adds only a few minutes. And the permit doesn't care either: fixtures are "utilization equipment," excluded from the fee's value-of-work basis, so a small job like this sits in Technical Safety BC's lowest tier whether it covers one fixture or two.

A quality 20W LED dusk-to-dawn fixture runs $80.55. So the two options on the day lamp #1 dies:

  • Replace only the dead one: $135 + $15 + $80.55 = $230.55
  • Replace both while I'm there: $135 + $15 + $80.55 + $80.55 = $311.10

The second fixture costs $80.55 today. Replaced later on its own trip, that same $80.55 fixture costs $230.55 — because it drags a fresh service visit and a fresh permit with it.

The "working" one isn't free either

Two problems with the survivor. First, it's on the clock: HPS lamps last 2–3 years on dusk-to-dawn duty, and it's the same vintage as the one that just died — figure roughly 2 years left, dimming the whole way.

Second, it's expensive to run while it waits. The lamp says 70W, but its magnetic ballast pushes real draw to about 90W — at ~12 hours a night and $0.14/kWh, that's $55 a year, against $12 a year for the 20W LED. The old fixture isn't waiting politely; it's billing you an extra $43 a year while it waits to die.

Ten years, side by side

10-year cost: one at a time vs both at once

Cumulative dollars spent on both fixture positions, starting the day lamp #1 dies. Hover or tap a point for exact totals.

Cumulative cost: replace only the dead fixture vs replace both now Replace only the dead one: $230.55 up front, about $67 per year while the old HPS survives, a $230.55 second visit when it dies around year 2, then $25 per year — $792 total by year 10. Replace both now: $311.10 up front and $25 per year — $556 by year 10. The both-at-once line is already cheaper before the second failure. $0$250$500$750 012345678910 years after the first lamp dies Replace only the dead one Replace both now the 2nd fixture dies: another $135 visit + $15 permit the deferred $80.55 goes out the wall in hydro in under 2 yrs One at a time: $792 Both at once: $556 Year 0 — one at a time: $230.55 (visit #1: $135 + $15 permit + 1 fixture) Year 1 — one at a time: $298 total Year 2 — one at a time: $596 total (2nd fixture dies — visit #2: $230.55) Year 3 — one at a time: $621 total Year 4 — one at a time: $645 total Year 5 — one at a time: $670 total Year 6 — one at a time: $694 total Year 7 — one at a time: $719 total Year 8 — one at a time: $743 total Year 9 — one at a time: $768 total Year 10 — one at a time: $792 total Year 0 — both at once: $311.10 (one visit: $135 + $15 permit + 2 fixtures) Year 1 — both at once: $336 total Year 2 — both at once: $360 total Year 3 — both at once: $385 total Year 4 — both at once: $409 total Year 5 — both at once: $434 total Year 6 — both at once: $458 total Year 7 — both at once: $483 total Year 8 — both at once: $507 total Year 9 — both at once: $532 total Year 10 — both at once: $556 total
Year One at a time Both at once
0$230.55 (visit #1)$311.10 (one visit, both fixtures)
1$298.00$335.63
2 (before lamp #2 dies)$365.45$360.16 (already ahead)
2 (after visit #2)$596.00 (visit #2: $230.55)$360.16
3$620.53$384.68
5$669.59$433.74
10$792.23$556.38

Where the $236 goes

The ten-year gap is $235.85, and it splits cleanly in two:

  • $150 — the duplicated trip. A second $135 service visit and a second $15 permit, to hang a fixture that could have gone up in a few extra minutes on the first visit. The fixture itself costs $80.55 either way; the overhead doesn't.
  • $86 — the survivor's hydro. Roughly two years of running a 90W HPS instead of a 20W LED, at $43 a year.

And notice the table at year 2: "both at once" is already the cheaper option before the second lamp even dies. The $80.55 you deferred goes out the wall in electricity in under two years. Everything from the second visit onward — all $236 of it — is pure premium for doing the job twice.

The timing assumption barely matters. If the second lamp somehow hangs on for 3 more years instead of 2, the hydro share grows to about $129 while the duplicated $150 stays exactly where it is — the gap gets wider, not narrower. The only way to avoid paying the visit and permit twice is to not book the truck twice.

The bottom line

When one of a matched pair of HPS fixtures dies, the second one isn't a separate future problem — it's the same problem, on a short delay, with its own $150 of overhead attached. Replacing both on one visit costs about $80 more today and roughly $236 less over ten years, and you never climb that ladder again.

"Just fix the broken one" isn't the frugal option. It's paying full freight, twice, for a job that was already half-covered the moment the truck arrived.

Figures: $135 service visit and $15 electrical permit per visit (fixtures are utilization equipment and don’t count toward the permit’s value-of-work basis); $80.55 per 20W LED dusk-to-dawn fixture; ~90W real input for a 70W HPS system (ballast losses included); ~12 hrs/night averaged over the year at $0.14/kWh; matched-age HPS lamps with 2–3 year dusk-to-dawn life, so the surviving lamp is assumed to fail ~2 years after the first. Prices before GST. Your rates and timing will vary — the direction of the math doesn't.

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Common questions

Should I replace both outdoor fixtures when only one has failed?

If they're the same vintage, almost always. The service visit and permit cost the same whether one fixture goes up or two — the fee mostly covers travel and making the circuit safe, and a second fixture adds only minutes to the job. Replaced later on its own trip, that same fixture drags a fresh visit fee and permit with it, and the surviving HPS burns an extra $40-plus a year in electricity while you wait.

How much does an HPS yard light cost to run?

More than its rating suggests. A 70W HPS lamp plus its magnetic ballast draws roughly 90W of real input. On dusk-to-dawn duty (about 12 hours a night averaged over the year) that is close to 395 kWh a year — around $55 at $0.14/kWh, versus about $12 for a 20W LED.

Do I need an electrical permit to replace a light fixture in BC?

Fixture replacement done by a licensed electrical contractor is carried out under a Technical Safety BC installation permit. Fixtures themselves are utilization equipment and don't count toward the permit's value-of-work basis, so a small job like this sits in the lowest fee tier — about $15 — whether the visit covers one fixture or several. That's part of why bundling fixtures onto one visit saves money.

Can I just put an LED bulb in my existing HPS fixture?

Retrofit LED lamps exist, but most need the ballast bypassed and rewired to line voltage, which is electrician work anyway — and you keep an aging fixture and socket. For a dusk-to-dawn light, a purpose-built LED fixture is usually the better spend.

MDN Electric
Matt Neuls — Red Seal electrician and owner of MDN Electric and General Repair in Prince George, BC. Two decades in the trade, from residential troubleshooting to pulp-mill controls.

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