EN 17037 §4.1 — Daylight provision
Part of EN 17037:2018. See that page for legal status.
Requirement
Two equivalent methods.
Method 1 — daylight factor
Each target illuminance converts to a daylight factor as D = target illuminance / Ev,d,med, where Ev,d,med is the median diffuse horizontal illuminance for the location (from EN 17037 Annex A). Every level sets two thresholds: a target DF over ≥ 50 % of the area, and a lower minimum-target DF over ≥ 95 % of the area.
The standard publishes the resulting daylight factors directly for 33 CEN capitals; here are the five relevant to this documentation:
| Location | Minimum (≥50% / ≥95%) | Medium (≥50% / ≥95%) | High (≥50% / ≥95%) |
|---|---|---|---|
| Stockholm | 2.5 % / 0.8 % | 4.1 % / 2.5 % | 6.2 % / 4.1 % |
| Oslo | 2.4 % / 0.8 % | 4.0 % / 2.4 % | 6.0 % / 4.0 % |
| Copenhagen | 2.1 % / 0.7 % | 3.5 % / 2.1 % | 5.3 % / 3.5 % |
| Helsinki | 2.2 % / 0.7 % | 3.7 % / 2.2 % | 5.6 % / 3.7 % |
| Reykjavík | 2.6 % / 0.9 % | 4.3 % / 2.6 % | 6.5 % / 4.3 % |
A separate table in the standard gives the same four illuminance levels for horizontal (rooflight-type) openings, converted from the global rather than diffuse illuminance since a horizontal opening also admits direct sun — those daylight factors come out lower for the same illuminance target.
Other Swedish cities (interpolated)
EN 17037 only tabulates capitals. For other Swedish cities relevant to LUX's users, the values below are LUX's own linear interpolation between the two nearest capitals in the standard's table, by geographical latitude — not figures published by the standard itself. Treat them as an approximation useful for early-stage checks, not a substitute for the standard's own capital-city values or a project-specific calculation.
| Location | Latitude | Minimum (≥50% / ≥95%) | Medium (≥50% / ≥95%) | High (≥50% / ≥95%) |
|---|---|---|---|---|
| Malmö | 55.6° | 2.1 % / 0.7 % | 3.5 % / 2.1 % | 5.3 % / 3.5 % |
| Gothenburg | 57.7° | 2.3 % / 0.8 % | 3.8 % / 2.3 % | 5.8 % / 3.8 % |
| Linköping | 58.4° | 2.4 % / 0.8 % | 3.9 % / 2.4 % | 5.9 % / 3.9 % |
| Uppsala | 59.9° | 2.5 % / 0.8 % | 4.1 % / 2.5 % | 6.2 % / 4.1 % |
| Umeå | 63.8° | 2.6 % / 0.9 % | 4.3 % / 2.6 % | 6.4 % / 4.3 % |
Malmö sits almost exactly at Copenhagen's latitude, so its values are effectively Copenhagen's own; Uppsala sits close enough to Stockholm's latitude to use Stockholm's values directly rather than interpolating. Linköping is interpolated between Copenhagen and Stockholm; Umeå between Helsinki and Reykjavík.
Method 2 — dynamic (climate-based)
Method 2 uses the same three target/minimum illuminance pairs as Method 1 above, but checks them directly against a full-year, sub-hourly climate-based simulation instead of converting to a daylight factor:
| Level | Target illuminance (≥ 50 % of area) | Minimum target illuminance (≥ 95 % of area) |
|---|---|---|
| Minimum | 300 lx | 100 lx |
| Medium | 500 lx | 300 lx |
| High | 750 lx | 500 lx |
In both cases the illuminance must be reached for at least half of the daylight hours (see the 4380-hour definition below).
Calculation setup
| Parameter | Value | Notes |
|---|---|---|
| Reference plane height | 0.85 m above floor | 0.75–0.85 m depending on national annex |
| Grid spacing | p = 0.5 · 5log₁₀(d) m, rounded down, max 1 m | d = longest room dimension when length/width ratio is 0.5–2, otherwise the shortest. Gives ≈ 0.2 m in small rooms up to ≈ 1 m in large ones |
| Wall offset (excluded border) | 0.5 m from every internal wall | |
| Sky model | CIE standard overcast for the DF method; climate-based (Perez, hourly weather file) for the illuminance method | |
| Daylight hours | The 4380 hours (half the year) with the highest diffuse horizontal illuminance in the weather file |
How LUX handles it
Status: 🔜 Planned, not yet supported in LUX Live v0.3.0 as a named EN 17037 report — LUX Live reports BFS 2024:8 and TEK17 by name instead, though the underlying computation is the same.
Method 1 maps directly onto the LUX daylight factor output, which is validated and in production use. Method 2 needs the daylight-autonomy model, which is in experimental development and not yet available in any LUX product.
Sources
See EN 17037's Sources.