About this calculator

Made for the planning stage

Recessed Light Calculator helps you estimate recessed light count, spacing and placement in a rectangular indoor room. It is for homeowners and anyone comparing a first layout before discussing the details with an installer or lighting designer.

Change the room dimensions, fixture specifications or target light level to see how the plan changes. Review the 2D layout, then save the inputs and coordinates as CSV, PNG or a printed report. The aim is to make those choices easier to understand—not to turn an estimate into an installation design.

How the estimate works

The calculator uses a simplified lumen-method estimate for maintained average illuminance: fixture count × lumens per fixture × utilization factor × light loss factor ÷ room area.

Auto mode looks for a complete grid that meets the light-count estimate and the assumed spacing limits. Presets and Custom mode keep your selected light positions even when the estimated brightness is below your target.

The IES lumen-method definition explains the general relationship between lighting, room characteristics and average workplane illuminance. It is a reference for the concept, not an endorsement of this calculator or a source for all its default values. This implementation uses a fixed utilization factor rather than modelling the room’s reflections.

Where the data comes from

Room light-level targets

The Room / use presets come from a BRE residential lighting modelling study. Editable starting values from a residential modelling study; not regulatory minima or verified current IES recommendations.

These are average targets across the calculation plane, not a minimum at every point. Kitchen, bathroom and home-office presets describe general lighting—not cabinet shadows, mirror-face illumination or individual task areas. You can enter a different target.

Fixture specifications

The 12 catalog entries below use manufacturer product pages or specification sheets for lumens, beam angle and watts. Values are per light, not per pack. Each entry identifies its reference configuration and the date its source was checked; ASIN identifies a listing rather than a manufacturer part number.

Published nominal output is used where noted. Values are not interpolated across color temperatures or dimming levels. Inclusion is not a product ranking, an availability guarantee or confirmation of installation suitability.

What we assume—and what we leave out

The following fixed values belong to this calculator. They are planning assumptions, not universal lighting requirements or values certified by the references above.

Utilization factor (UF)

0.55

Light loss factor (LLF)

0.8

Spacing / mounting height ratio

1.5

Floor = 0 m. The suggested 0.75 m table/desk and 0.9 m worktop heights are calculator assumptions, not heights specified in the source tables. Use your actual surface height.

The heatmap, minimum, maximum and uniformity estimates use the same 32 × 32 sampling grid and a symmetric beam approximation scaled to the lumen-method average. They are illustrative estimates, not measured illuminance or an IES-file photometric simulation.

The tool does not assess obstructions, detailed reflections, glare, electrical circuits or code compliance. Total watts are a sum of fixture power only. Review the final layout, product suitability and installation requirements with a qualified professional.

Source checks & updates

The dates above record source checks, not continuous monitoring or a claim that a document is the latest edition. Manufacturer specifications may change; check the linked source for the exact model and configuration before purchasing.

The calculator, this page and exported reports use the same room-target and fixture catalogs. Manufacturer attribution applies only to the listed specifications. Choosing Custom specs keeps your numbers but removes the manufacturer identity.

For any discrepancy, the useful details are the model or room preset, the value in question, and the supporting source with its version or date. You can send a correction; source-backed values and calculator assumptions are kept separate so that each can be checked on its own terms.