What Does an LED Retrofit Actually Save?
Your fixture count, your hours, your rate. This gives you the annual saving, and if you have been quoted a price it gives you the payback. Energy only, with nothing assumed in our favour.
How the Saving Is Worked Out
The Ballast Is Where Most Comparisons Cheat
A two-lamp fluorescent fitting with 32 watt lamps is not a 64 watt fixture. Once the ballast is counted it draws about 59 watts at the panel, and an old magnetic ballast on T12 lamps takes considerably more. Plenty of published comparisons use the number printed on the lamp, which understates what the fixture actually costs you to run and, oddly, understates the saving too.
The before figures here are fixture wattages including the ballast, which is what your meter sees and what your bill is calculated from. The after figures are typical for a like-for-like LED replacement rather than for the brightest unit on the market.
What Is Left Out, and Why That Matters
This counts energy and nothing else. It does not count the lamps and ballasts you stop replacing, the lift hire and the callouts that go with changing a high bay, the utility rebates New Hampshire programmes offer on commercial lighting, or the cooling load that disappears when a fixture stops turning most of its power into heat.
All four are real and all four make the payback shorter than the number above. They are left out because they depend on the building, the programme year and how the space is used, and building them into a calculator would mean guessing in our own favour. Treat the figure here as the floor.
Retrofit Questions, Answered
Why Is Your "Before" Wattage Higher Than What Is Printed on the Lamp?
Because the lamp is not the only thing drawing power. A two-lamp T8 fixture with 32 watt lamps draws about 59 watts at the panel once the ballast is counted, not 64 and certainly not 32. Published comparisons that use the lamp figure alone understate both the current draw and the saving. The figures here include the ballast, which is what your meter sees.
What Is a Realistic Payback?
For high-wattage fixtures burning long hours, often faster than people expect: metal halide high bays in a warehouse running two shifts are usually the quickest win in any building. For a handful of office downlights on 50 hours a week it can be years, and the honest answer there is that lighting quality and maintenance are the reason to do it, not the energy bill.
Does This Include Rebates?
No, deliberately. New Hampshire utility efficiency programmes do offer commercial lighting incentives and they can move the number a lot, but what you qualify for depends on the fixtures, the controls and the programme year. Building that into a calculator would be guessing in our own favour. Treat anything you get back as shortening the payback shown here.
Is a Lamp-Only Retrofit as Good as Changing the Fixture?
It is cheaper and quicker and it saves most of the energy, but it keeps the old housing, the old reflector and the old wiring. Where the fixtures are sound it is often the right call. Where they are corroded, damaged or badly laid out for the space, you are paying to put new lamps in the wrong fixtures in the wrong places, and a redesign is worth pricing alongside it.
Can the Work Happen Without Shutting the Building?
Usually, yes. Lighting is one of the easier things to phase because it goes area by area and circuit by circuit, out of hours where it matters. The part that needs planning is anything at the panel, which is minutes rather than hours but has to be scheduled.