Room dimensions and surfaces
Measured floor area, ceiling height, and surface colours. The utilization factor in any screen is only as good as the room it is applied to.
Methodology
How Lighting Calculator calculates.
Explicit-input models with visible formulas, dated baselines, machine-checked test cases, and a stated verification boundary. Screening-grade lighting arithmetic, not a photometric study or a code compliance model.
The principle
Every result must be reproducible from the inputs on the page.
Each calculator is a fixed formula over labeled inputs. There are no hidden scores, no black-box adjustments, and no location lookups: the numbers you type, plus the stated defaults, fully determine the outputs. Every calculator page shows its formula, and every calculator ships with automated test cases that fixed inputs must reproduce before publication.
Units and conventions
One consistent system across all ten tools.
Lumens vs lux
Lumens measure light leaving the fixture; lux measures light arriving on the surface. One lux is one lumen per square metre, and one foot-candle is one lumen per square foot. Counts are bought in lumens; adequacy is judged in lux.
Power vs energy
Watts describe the connected lighting load; watt-hours describe the energy it consumes. Cost always derives from kWh multiplied by a rate. Delivered lumens and input watts are kept separate: efficacy connects them, and neither is guessed from the other.
Money handling
Rates are entered in cents per kWh and converted once, at a single documented step, to dollars. Displayed money rounds to cents; intermediate values keep full precision so chained steps do not drift.
Maintenance and utilization
Two factors carry everything the room does to the light: the utilization factor carries room surfaces and luminaire distribution, and the maintenance factor carries dirt and ageing. Both stay editable on every calculator that uses them, and both default to the conservative side of normal practice.
Precision statement
Outputs are screening-grade: good enough to rank options, size a first pass, or check a quote. They do not replace a photometric study with the manufacturer IES files, a code compliance model, or a measured illuminance reading.
Method by category
What each tool family models, and what it assumes.
Spaces and applications
Illuminance targets come from published recommended ranges for the activity in the space, and every one of them stays editable. The lumen requirement multiplies the target by the floor area and divides by the maintenance factor, so the figure is the light the fixtures must produce on day one, not the light the room needs at the end of the cleaning cycle.
Fixture configuration
Counts and loads are treated separately: the delivery side uses lumens, the distribution side uses watts, and a service factor connects them only where the input says so. Driver load is computed on apparent power, and circuits are limited to the eighty percent continuous-load share of the breaker.
Layout and installation
Spacing is the tighter of two rules: the spacing-to-mounting-height limit for the photometric distribution, and the spacing that just meets the illuminance target. Wall and end-of-row offsets, obstructions, and uniformity stay outside the screen and belong in the point-by-point check.
Lighting in operation
Energy is connected kilowatts times operating hours, priced at the rate you enter. Control savings are applied as a reduction in hours or output rather than as a discount on the result, and the emission figure carries the grid factor it was calculated with.
Energy retrofit
A retrofit is measured as the difference between the existing load and the replacement load, at the same hours and the same rate. Payback divides the installed cost after incentives by the annual saving, and lifetime figures are undiscounted and say so.
Sources and baselines
Dated numbers, named sources, annual review.
Energy price baselines
Average cents per kWh come from U.S. Energy Information Administration monthly tables and carry the year they were taken from. They are comparison baselines; your own tariff replaces them in any decision.
Illuminance and code references
Recommended illuminance values follow published IES practice, and power density allowances are labelled as code screening values. Neither is a compliance determination: the adopted code edition and the authority having jurisdiction govern the project.
Equipment figures
Typical wattages, COP ranges, and lifespans are labeled as starting points. Nameplate data and manufacturer sheets replace them during verification.
Verification protocol
Replace these five before relying on any result.
Photometric data
The manufacturer IES file for the actual luminaire: delivered lumens, distribution, and spacing-to-height behaviour. Catalogue lumen figures are not photometry.
Governing code and standard
The adopted code edition, the illumination standard the project is designed to, and any client standard that overrides both.
Operating schedule and tariff
Actual hours from a controls schedule or a log, and the all-in energy price including demand and fixed charges.
Qualified review
Verification by a lighting professional, electrician, or energy engineer, and a measured illuminance check after installation, before anyone relies on the numbers.
Illuminance targets and allowance values are dated screening references, not live code lookups. Calculator results are first passes, not photometric studies, compliance documents, quotes, or guarantees.
Known limits
What these tools deliberately do not do.
No code compliance
Nothing here determines whether a lighting design complies with the adopted energy code or an illumination standard. Power density, illuminance, and control credits are project decisions under the authority having jurisdiction.
No point-by-point photometry
Average illuminance is not uniformity. Dark bands between fixtures, wall grazing, rack shadows, and glare require a point-by-point model with the real photometric file.
No measured baselines
Hours, ageing, and existing loads are estimates until they are logged. Two buildings with identical drawings can differ by a third of the energy, and only measurement shows which one you have.
No incentive administration
Rebate and incentive figures are entered by you. Programme rules, pre-approval deadlines, and verification requirements come from the programme administrator, not from this site.