In a tender file, the page that circulates most is never the table of results. It is the colour image, green in the middle and blue in the corners, that everyone looks at first. It reads quickly, it convinces quickly, and it can be manipulated just as quickly depending on the palette chosen by whoever produced it.
What a false colour map represents
A false colour rendering displays, on a given calculation surface, the illuminance value point by point. Each range of values corresponds to a conventional colour. The image does not show the light as it would be seen on site: it translates a numerical result into a visual gradient.
The map is produced by the calculation engine from the model of the room, the photometric files of the luminaires and the maintenance factor used. It belongs to the same set of documents as the layout plan, the isolux curves and the tables of values. Taken alone, it proves nothing. Cross-checked with the other documents of a photometric study, it becomes a quick and reliable checking tool.
The scale: the first thing to look at
Two maps of the same room can give two opposite impressions depending on the limits of the scale. A scale that starts low and stops just above the average drowns the differences in a reassuring flat green. A scale tightened around the target value, on the contrary, brings out every variation.
Three questions arise in front of any map:
- What are the minimum and maximum limits of the scale, and are they shown with their unit.
- Are the steps regular, or tightened in certain ranges only.
- Does the maintained illuminance required for this room appear explicitly on the scale.
A map without a legible scale remains unusable. Asking for one is the first correction to make to a report received.
Spotting dark areas and over-intensities
Once the scale has been validated, the reading turns to the geography of the room. The cold areas of the palette signal dips in illuminance: corners, the back of a bay, around columns, the edges under the eaves. These dips are only a problem if they fall on a task area.
The hot areas signal excess. A very intense spot under each luminaire often indicates spacing that is too small, or an optic too concentrated for the mounting height. Excess power costs in consumption and comfort, without improving the useful value at the workstation.
The spotting is always done in relation to the layout of the furniture. A map presented without racks, machines or partitions describes an empty room, never the room in use.
Reading uniformity on the image rather than in the table
Uniformity U0 is the ratio between the minimum illuminance and the average illuminance of a surface. The table gives it as a single value, the map shows where this minimum lies. This information changes the decision.
A minimum located in a corner of a circulation area calls for a different treatment from a minimum located in the middle of an assembly station. The map also shows whether the dip is localised or extends over a whole bay, which no average value says.
Map at floor level and map on the working plane
A map only makes sense together with the height of its calculation surface. Three surfaces come up constantly.
Calculation surface | What it describes | Typical use |
|---|---|---|
At floor level | Illuminance received at floor level | Circulation areas, warehouse aisles, car parks, outdoor areas |
On the working plane | Illuminance received at the height of the visual task | Offices, workbenches, assembly stations, inspection tables |
Vertical | Illuminance received on a vertical face | Rack faces, docks, panels, faces |
Comparing the floor-level map of one project with the working-plane map of another makes no sense. In storage aisles, the vertical map of the rack faces is often more decisive than the floor map, because the task consists of reading a label and not of walking.
Renderings that artificially flatter a project
A few presentation choices flatter a result without falsifying it in the strict sense. They are quickly spotted.
- A map calculated when new, without a maintenance factor, and therefore at the best moment in the life of the installation.
- A room modelled empty, without furniture or obstacles, which removes all cast shadows.
- Optimistic reflectances on surfaces that, on site, are dark or dusty.
- A calculation surface reduced to the central part of the room, the edges simply being excluded from the rendering.
- A scale whose upper limit is very high, which visually flattens the differences towards the bottom.
These settings appear in the parameter pages of the report. A report that does not publish them must be completed before any purchase decision.
Comparing the map with the figures
The final check consists of matching three elements: the requirement that applies to the room, the values in the table and the image. If all three tell the same story, the map is reliable.
- Identify the maintained illuminance and uniformity required for the task, based on the compliance requirements that apply to the room.
- Note in the table the average illuminance, the minimum, the maximum and the uniformity over the task area.
- Check on the map that the minimum in the table is indeed located where the image suggests.
- Check the height of the calculation plane and the maintenance factor used.
On an existing installation, the map is also compared with the ground. Lux meter readings taken during an on-site lighting audit make it possible to adjust the model and explain the gaps found. For a storage building, studies on luminaires for industrial warehouses are best requested with the vertical map of the rack faces in addition to the floor map.
Send us the report you received and request a review of your lighting study.
