Designing with daylight: drawing light, not windows

One of the first things we ask architecture students is this: where does the light enter this room at three o’clock? The answer usually comes as the position of a window. Yet the window is only the doorway for light; the real design is what light does once it is inside. Does it wash a wall, bounce off a ceiling, settle on a table? Before we start drawing a plan in the studio, we draw the sun’s journey across the site at the summer and winter solstices, morning and evening.

North light is something painters and sculptors have known for centuries: nearly constant through the day, shadowless and true to colour. That is why we lit the reading hall of the City Library entirely with north-facing rooflights. Direct sun never falls on the tables; readers see no glare on the page, yet the hall stays bright all day. We use the same principle when designing a ceramics studio; the true colour of glazes can only be seen in this light.

Southern light is another story. It is warm, it moves, and its angle changes with the seasons. In a Mediterranean climate the real question on a south facade is not getting light but getting it at the right time. We calculated the eave depth of the Rock House against the angles of the June and December sun: in summer the midday sun never touches the glass, in winter it reaches the back wall of the living room. The eave here is not decoration but an instrument that separates the seasons.

The daylight factor is the ratio of illuminance inside a room to that outside under an overcast sky, and it predicts quite well how bright a room will feel. But numbers don’t tell everything. Two rooms with the same daylight factor feel completely different if one is lit by a single large window and the other from two directions. Light from two sides softens shadows, flatters faces and makes a room truly liveable. That is why, in housing, we look for dual-aspect rooms wherever we can.

Light and darkness are not opposites but complements. A space lit evenly in every corner is dull; the eye looks for somewhere to rest, a corner in shade. In the Olive Grove Courtyard House we kept the external windows deliberately small and deep; the courtyard became where light really enters. This created a gentle gradient between brightness and dimness in the rooms. The reading chair sits by the window, the bed in the darker corner. To design light is also to design shadow.

Artificial light should pick up where daylight leaves off. The most common mistake in night lighting is trying to imitate daytime light levels. We prefer evening light that is low, warm and fragmented: rather than a single strong source from the ceiling, a lamp over the table, a hidden strip washing a wall, a small light inside a shelf. The space stays layered at night, and from outside the building shows itself through a few quiet windows.

One last note: lighting design is learned not from a spreadsheet but from models and patience. In our studio we build a 1:20 light model of every important space and watch it for hours under a lamp imitating the sun’s angle. Only then do we see how much difference it makes to deepen a window reveal by five centimetres or leave a ceiling pale. When the building is finished, nobody notices any of this; people simply say it feels good to be there.