Illuminance evaluation in Revit: Em per room from the model instead of from feel

Illuminance evaluation in Revit: Em per room from the model, room and component schedules, model audit — as evidence for the client.

DIN EN 12464-1

The question that always comes too late

“Is there enough light in the offices?” — clients rarely ask that at the start. It comes when the drawings are done, and it comes with the expectation that the answer exists in numbers. Room by room, with a value you can hold against a requirement.

Anyone who distributed the luminaires from experience — and in an electrical set that is the normal case, because the lighting calculation often sits in another program and sometimes in another office — does not have those numbers. What they have is a model with luminaires in it.

How people get to the numbers otherwise

The clean route is a lighting calculation in a dedicated program. It is more accurate than anything a model can give you, and it is the evidence nobody replaces in the end. But it costs time and assumes a coordinated state — rooms, reflectances, luminaire type. For the question “are we roughly right?” it is too heavy.

The quick route is an estimate by hand: area times target value, divided by luminous flux times efficiency, plus a maintenance factor. You will happily do that for three rooms; for sixty you will not. And when the luminaire type changes you start again.

What the module takes over

The reporting module runs the estimate for all rooms at once. The command Beleuchtung Em/Raum returns a value per room that you can hold against a requirement — in a schedule you can export.

The other half of the same calculation sits in the fit-out module: there the automation places as many luminaires per room as it takes to reach a given target illuminance, evenly, as a grid. It calculates by the utilisation factor method, n = E·A / (Φ·UF·MF); luminaire type and luminous flux come from a luminaire selected beforehand. Layout and distribution therefore happen in one step, and the evaluation checks afterwards.

The module contains further evaluations built on the same data: a room schedule listing the components per room — the basis for the cabling — a component schedule, a detector check, a model audit with the usual quality figures (warnings, unused types, in-place families, CAD imports, views not on a sheet, unplaced rooms) and the removal of duplicates.

The schedules are not output only: values can be edited in them and are written back to the component parameters, with feedback on what was actually stored and what was not. That is the difference from an export you then reconcile by hand.

What the estimate depends on

Four quantities determine the result, and three of them are in the model: the room area, the target value you give, and the luminous flux of the chosen luminaire. The fourth — the utilisation factor together with the maintenance factor — is an assumption. That is exactly where this parts company with a proper lighting calculation, and exactly where you should know what you are calculating with.

In practice: select the luminaire type first, so that flux and form are right. Calculate with an arbitrary luminaire and you calculate an arbitrary result. And the rooms have to know their area — unplaced or unbounded rooms drop out of the evaluation. The model audit in the same module shows them, and it is worth running before the evaluation.

The value per room is then solid enough for “luminaires are missing here” or “we are generous here”. It is not solid enough for “this is exactly 512 lux”.

What the client gets to see

A table with one row per room, a target and an actual value, is a document you can talk about in a meeting. It answers the question about light, it shows at the same time which rooms were considered at all, and it makes visible where a closer look is needed.

The same holds for the module's other evaluations. The room schedule with the components per room is the basis for the cabling and at the same time the answer to “how many sockets are actually in there”. The model audit answers the more uncomfortable question of what state the model is in — before somebody else asks it.

Because the schedules can write values back, they are a working tool and not just a report: what gets decided in the meeting can be entered on the spot, and the tool reports back what actually reached the model.

Standards

The target value comes from DIN EN 12464-1 — the document named for this tool in the shop. It sets out which illuminance is intended for which activity; the tool calculates against the value you give it.

The classification matters: the utilisation factor method is an estimate. It does not replace a lighting calculation with room geometry, reflectances and luminaire data, and it is no good as evidence to an authority. It is good for seeing early where it gets tight — and for seeing it in every room at once, instead of in the three you had time for.

In practice this is the order that saves time: lay out and evaluate roughly first, correct the conspicuous rooms, and only then commission the exact calculation. What arrives there is then already a coordinated state — not a first draft that makes the calculation necessary twice.

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