Blind Solutions Academy · C19 · A4 Quick Reference

Daylighting & Glare Cheat Sheet

Metric targets, glare thresholds and decision trees on four pages — the working numbers for the desk and the design review.

Page 1 · Daylight-metric targets

Quantity, over-lighting & the bands

sDA300/50% — spatial Daylight Autonomy

% of floor ≥ 300 lux for ≥ 50% of occupied hours/yr (IES LM-83). ≥ 75% preferred, ≥ 55% nominally accepted. Higher is better.

ASE1000/250h — Annual Sun Exposure

% of floor ≥ 1,000 lux of direct sun for ≥ 250 hr/yr, shading open (LM-83). ≤ 10% ceiling, ≤ 7% preferred. Lower is better.

Daylight Factor (DF)

Ei/Eo under overcast sky. Concept screen only. DF 2% general / 5% daylight-dominated. Orientation-blind, glare-blind — never decide on DF alone.

Task illuminance

~300-500 lux general office/reading (SANS 10114-1). Validates adequacy, not comfort.

UDI — Useful Daylight Illuminance bands

% of occupied hours in each band:

Fell short
<100 lux

Supplementary
100-300

Autonomous
300-3,000

Exceeded
>3,000 lux

Goal: maximise UDI-autonomous; keep fell-short and exceeded low. UDI-exceeded = over-lighting / glare flag. Some formulations cap autonomous at 2,000 lux — state your band edges.

Read sDA + ASE together. High sDA + high ASE = plenty of light, all intolerable beam → blinds down → in-use daylight collapses. Drive ASE < 10% while holding sDA ≥ target.

Page 2 · Glare, view & circadian thresholds

Comfort, view & health numbers

Daylight Glare Probability (DGP)

DGP	Class
< 0.35	Imperceptible
0.35 - 0.40	Perceptible
0.40 - 0.45	Disturbing
> 0.45	Intolerable

Design ceiling: DGP ≤ 0.40 for most occupied hours; ≤ 0.35 for demanding tasks. Evaluate from an HDR luminance map at the occupant eye, across the year.

DGI (legacy)

~18 just perceptible → ~28 just intolerable. Superseded by DGP for daylight.

Luminance ratio (task : surround)

Comfortable 1:10 to 1:20. A 450 lux desk vs 8,000 cd/m² sky = ~1:50 → glare.

EN 17037 view out (3 tiers)

Graded on: (1) horizontal sight angle, (2) outside viewing distance, (3) number of view layers seen — sky / landscape / ground. Protect the eye-level landscape layer.

Circadian (WELL)

Melanopic EDI at the eye

Target ~150-240 melanopic lux (vertical, at eye) by day per WELL options. ipRGC peak ~480 nm; lux under-counts blue-rich daylight.

Fabric openness factor

1-3% = strong glare/luminance control, veiled view. 5-10% = clearer view, more transmitted brightness. Match to orientation luminance.

VLT & LSG = VLT / SHGC

LSG > ~1.25 = spectrally selective (daylight in, heat out) — preserves circadian quality.

Page 3 · Decision trees

From metric to move

Quantity & distribution tree

sDA below target?

Deep zone dark? → raise window head / add clerestory (light reaches ~1.5-2× head height)

Still patchy? → add light shelf (bounce to ceiling) + lift reflectances (ceiling ≥0.8, walls ≥0.5)

Deep-plan / no perimeter? → toplighting: roof monitor or sawtooth, controlled orientation

Raising sDA pushed ASE up? → go to glare tree — redistribute, don't just add

Over-lighting tree

ASE > 10% or UDI-exceeded high?

Direct beam deep in space → external shading geometry + selective glazing

Residual brightness → dynamic shading, hour by hour

Glare tree (DGP)

DGP > ceiling at occupant eye?

Bright source in line of sight? → rotate workstation / shift view direction first

Reduce source luminance → shading + lower-VLT / selective glazing + diffusing fabric

Lift surround luminance → light interior finishes raise adaptation, cut relative contrast

Need view kept? → venetian (angle slats) / top-down blind preserves landscape layer

Static vs dynamic tree

Do the goals conflict over the day?

Yes (almost always) → dynamic shading under DGP/ASE control

External (high ASE) vs internal (paired w/ selective glass)

Always add manual override + timed auto-return

Page 4 · Worked snapshots & standards

Numbers & frameworks to remember

West studio (Joburg) — the trade

	As built	Engineered
sDA300/50%	80%	~78% (in-use)
ASE1000/250h	28%	< 10%
Peak DGP	0.46 (intol.)	0.33 (imperc.)

Selective glazing + DGP-driven external venetian. In-use sDA recovers because automation retracts the moment glare passes.

Daylight penetration

Useful side-light depth ≈ 1.5-2 × window-head height. Head 2.7 m → ~5.4 m; add clerestory to 3.6 m → ~7.2 m.

Standards quick map

Framework	Use
IES LM-83	Defines sDA & ASE (thresholds + method)
EN 17037	Daylight provision, view, sunlight, glare
SANS 204	Energy efficiency; daylight harvesting cuts load
SANS 10400-XA	Energy usage regulation framework
SANS 10114-1	Interior lighting / illuminance targets
Green Star SA	IEQ credits: daylight + glare control
WELL	Circadian (melanopic EDI) + visual comfort

External > internal for ASE: an external device intercepts beam outside the glass, controlling overheating as well as glare; internal devices pair with selective glazing.