Daylight factor for lighting calculation notes
Daylight factor notes the relationship between an indoor task-plane reading and an outdoor reference reading from the same daylight condition. It supports daylight contribution notes before artificial lighting, controls or room-lighting estimates are finalised.
Daylight-factor sequence
A clean daylight note keeps measured readings, sun condition, the assessed plane and the artificial-light target in separate fields.
- 1Note the plane
Name the desk, bench, floor path or vertical surface being measured.
- 2Measure indoors and outdoors together
Take indoor daylight and outdoor reference readings at the same time.
- 3Set a reference condition
Enter the outdoor condition used for the indoor daylight contribution estimate.
- 4Compare with the target
Read the daylight contribution before carrying the remaining target to a lighting calculation.
Application search intent fit
Focus daylight searches on one simultaneous reading set before artificial-light or control notes are added.
| Search phrasing | Calculator note | Carry forward |
|---|---|---|
| Daylight factor calculator | Indoor task-plane lux, outdoor reference lux and entered factor for one daylight condition. | Time, sky state, assessed plane, blind state and daylight-factor examples table. |
| Home office daylight | Desk reading separated from screen direction and window or shade condition. | Desk position, screen reflection, control zone and remaining artificial-light target. |
| Skylight daylight contribution | Indoor reading under the roof opening compared with the same-time outdoor reference. | Aperture, shaft or diffuser condition, direct-sun note and contrast check. |
| Perimeter office daylight | Facade-row reading set before deeper office rows are judged separately. | Distance from glazing, switching zone, sensor position and later lux readings. |
Measurement note
A daylight factor without a measurement note can be misleading because daylight changes quickly across the day and across the room.
| Note item | Why it matters | Technical note |
|---|---|---|
| Indoor plane | Readings change between floor, desk, bench, wall and shelf face. | State plane height, orientation and the exact point or grid used; compare the note shape with the daylight-factor examples table. |
| Outdoor reading | The percentage depends directly on the exterior reference value. | Note the value at the same time, on the same reference basis and away from local obstruction. |
| Sky condition | Clear sun, cloud, shade and reflected light can change readings by large margins. | State whether direct sun was excluded from the factor or recorded as a separate glare condition. |
| Room state | Blinds, doors, screens and furniture can change the daylight path. | Note the room condition before comparing later measurements. |
| Meter handling | Tilted sensors, body shade and moving shadows can bias a small reading set. | Keep the sensor level on the assessed plane and repeat doubtful points. |
Result interpretation
Daylight contribution should be read beside the maintained-light target, not as a replacement for the room-lighting calculation.
| Result | Technical meaning | Lighting follow-up |
|---|---|---|
| Measured daylight factor | Indoor daylight reading divided by the simultaneous outdoor reference, expressed as a percentage. | Compare readings only when the measurement setup is similar. |
| Estimated indoor daylight | Outdoor condition multiplied by the entered daylight factor. | Carry the value as daylight contribution for the named plane. |
| Target covered | Estimated indoor daylight divided by the target lux. | High values still need glare, contrast, shade position and time-of-day checks. |
| Remaining target | Target lux minus estimated indoor daylight, floored at zero. | Artificial-light sizing still needs luminaire output, UF, MF and layout checks. |
Artificial-light boundary
The daylight number should stay visible beside the electric-light estimate instead of being blended into one unsupported room result.
| Boundary | Why it stays distinct | Note for the next check |
|---|---|---|
| Daylight contribution | It depends on exterior condition, shade state and whether direct sun or glare was excluded from the factor. | Carry the reference outdoor lux, daylight factor, assessed plane and sun/glare note. |
| Electric-light capacity | The installed lighting must still serve evening, overcast and shaded operation. | Carry target lux, remaining lux, luminaire output, UF, MF and layout evidence. |
| Controls | Daylight-responsive control only makes sense where daylight reaches the same controlled zone. | Note perimeter grouping, switching or dimming zone and sensor location if known. |
| Australian sun and glare | Strong sun can raise lux while reducing visual comfort through contrast or reflection. | Note direct sun, blind state, screen direction, glossy surfaces and hard shadows. |
Daylight factor is a relationship
Daylight factor is not an indoor lux target. It is the percentage relationship between an indoor daylight reading and an outdoor reference reading. A room can have a modest daylight factor and still feel bright during strong exterior daylight, or feel dim when the outdoor condition drops.
That relationship is useful because it keeps the indoor reading tied to the exterior condition. A note that says 120 lx was measured indoors means little without knowing whether the outdoor reference was 2,000 lx, 10,000 lx or a sun-affected value.
Measure the task plane, not the room name
A room label does not define the daylight result. A home office desk beside a window, a desk against the opposite wall and a screen facing a bright aperture can all produce different readings in the same room.
The assessed plane should be named before the number is recorded. Desktop height, benchtop height, floor path and vertical display surfaces each describe a different visibility problem. The daylight factor belongs to that plane, that point or grid, and that room condition.
Outdoor readings need the same timestamp
Daylight can change faster than most artificial-light readings. Passing cloud, direct sun, shade and time of day can move the outdoor reference value dramatically. Indoor and outdoor readings should therefore belong to the same moment, or to a very short repeated sequence.
When the readings are not simultaneous, the daylight factor becomes weak evidence. A later outdoor value may describe a different sky condition from the one that produced the indoor reading. The timestamp, outdoor reference position and sky note matter as much as the numbers.
Direct sun can distort the note
A patch of direct sun on a desk can create a high indoor reading while the rest of the task area remains poor or uncomfortable. That reading may say more about glare and contrast than useful working light.
Australian interiors often move between bright sun, deep shade and high contrast during the same day. The measured condition should state whether direct sun reached the assessed plane or was excluded from the factor. If glare, veiling reflections or hard shadows are present, note daylight contribution beside a comfort note rather than treating it as free task light.
Contribution is not availability
Estimated indoor daylight shows the contribution under the entered outdoor condition. It does not say how many hours that contribution is available, how often blinds are closed or whether occupants accept the glare condition that produced the reading.
That distinction matters in Australian homes and workplaces with strong sun angles, verandahs, eaves, tinted glazing and seasonal shade. A space may have high daylight for part of the day and still need stable electric light for overcast periods, evening use, screen tasks or shaded operation.
Carry daylight separately from electric light
Daylight contribution and electric-light capacity should remain separate in early notes. Electric lighting still needs luminaire output, utilisation factor, maintenance factor, beam control, switching and glare review.
Keeping the daylight value separate makes control discussions clearer. Perimeter rows, dimming groups and daylight-responsive controls depend on where daylight is available, whether that area matches the controlled zone and whether the room still works when daylight is absent.
Perimeter zones need their own reading set
Daylight is rarely distributed evenly across a deep room. A row of desks near the facade, a central work area and a rear circulation path may each deserve separate readings. Averaging them into one room number can hide the strong daylight gradient that people actually experience.
Where a lighting group is switched or dimmed separately near windows, the daylight factor note should follow that group boundary. A perimeter row can then carry its own daylight contribution while the inner zone keeps a different artificial-light allowance.
Home offices need screen-aware readings
A desk can have enough measured daylight and still be uncomfortable when the screen faces a bright window or when sunlight lands across the keyboard. The daylight factor notes quantity, not reflected glare or contrast on the display.
For home offices, note desk orientation, screen direction, blind state, bright background and time of day with the lux readings. The lighting note can then separate useful daylight from conditions that require shading or a different task-light arrangement.
Skylights and roof windows need context
Skylights and roof windows can raise indoor daylight strongly, but the result depends on aperture size, shaft depth, diffuser condition, orientation and roof shading. A daylight factor reading captures the measured condition rather than approving the aperture.
Where daylight is being compared before and after a roof-light change, keep the same measured plane, similar sky note and the same room state. Otherwise the comparison may reflect weather, shade or time more than the building change.