The ROI
$115,000 saved. A million destroyed.
That is what one value-engineering decision can do: cut a lighting line item, and erase roughly $102,700 a year in health costs and $12,000 a year in energy along with it. The savings are visible. The loss is not.
01. The loss
Translation failures, not technical failures
Lighting specifications rarely lose on their merits. They lose at cost review, because finance sees a line item where the design team sees a risk-adjusted return. Every certified project gets a value-engineering review, every one, and a spec that cannot be read as capital expenditure with measurable operating payback does not survive it.
810hours
of value-engineering rework a year, for a ten-person lighting design team
86%
of staff do that rework unpaid, an industry-wide pattern, not one firm's problem
$240K
of lost commission across a ten-person lighting sales team
From a survey of 30+ lighting industry executives at the Illuminating Engineering Society, Toronto, September–October 2025.
The gap is structural. California’s Title 24 lighting standards, like every energy code, account for watts, not people. Human performance cost is excluded from the calculation entirely, which means the one number that would defend the specification is the one number nobody is required to produce.
02. The model
A ninefold return, and where it comes from
The base case runs a 100-person workforce across 200 fixtures over ten years. Installation is a one-time $115,000. Against it sit two recurring savings: the workforce health costs that better circadian light avoids, and the energy the new scheme does not use. The payback lands at roughly eleven months.
| Line | Year 1 | 10-year total |
|---|---|---|
| Installation cost | ($115,000) | ($115,000) |
| Health-cost savings (65% light attribution) | $102,703 | $1,027,030 |
| Energy savings | $12,000 | $120,000 |
| Net benefit | $99,703 | $1,032,030 |
9:1
return over the ten-year horizon
~11 months
to pay back the installation
65%
of circadian rhythm is regulated by light
03. The method
Every assumption, stated
A number survives a cost review only if the room can see how it was built. These are the inputs behind the base case.
- 5% discount rate, over a 10-year horizon, with scenarios also run at 3% and 7%.
- Productivity uplift of 0.5–2.0%, taken net of presenteeism, fatigue, and turnover.
- A 65% light-attribution factor applied to workforce health costs: the share of circadian regulation driven by light.
- A 100-person workforce across 200 fixtures. Every model is recalibrated to the actual workforce size, role mix, and occupancy profile.
How confident is this
Directional, and pre-pilot. The model is built on peer-reviewed research and recalibrated per project, but it is not investment-grade evidence and we do not present it as such. Controlled data comes from the pilots now in the field, which is the entire point of running a pilot before anyone commits capital.
04. Money already on the table
Most projects leave the incentives behind
Between 75% and 77% of commercial projects have rebate access they never capture. Earthlight quantifies what is available per project (the 179D deduction, utility rebates, and state programs) as part of the same model, because an incentive nobody claimed is indistinguishable from an incentive that did not exist.
The modeling behind this work informed the WELL v2 lighting standards, which protect specifications in roughly 74,000 buildings worldwide, and was recognized by the Illuminating Engineering Society as a significant advancement in the art and science of light.
Run the model on your building.
Every figure here recalibrates to your workforce, your fixtures, and your occupancy. The assessment is where that starts.