Lighting A Staircase Is About Seeing The Edge Of Each Tread

A brightly lit staircase can still be difficult to use. What the foot needs is not brightness but a visible edge to each tread, and that is a question of direction.

The eye reads steps by contrast at the nosing

Descending a stair, the useful information is where each tread ends. That edge shows up as a line only if the tread surface and the riser below differ in brightness.

Light arriving from above and in front creates that difference reliably, because the horizontal surface catches it and the vertical one falls into shadow.

Flat, even light from every direction removes the difference entirely. The stair becomes a uniform slope to the eye, which is exactly when people misjudge it.

Going down is harder than going up

Climbing, the treads are ahead and their surfaces are turned towards you. Descending, you see mostly the nosings, and the surfaces are hidden.

Any light source at the bottom of a flight shines into the eyes of someone coming down, which reduces adaptation at the moment it is most needed.

Positioning fittings so they light the treads without being in the descending sightline is the single largest improvement most stairs can be given.

Landings need their own treatment

A change of direction is where the pattern of steps breaks, and it needs to be legible before the walker arrives at it.

Half-landings in particular benefit from a brightness change, so that the eye registers a pause rather than continuing to expect regular treads.

Winders, where treads narrow towards the inside of a turn, are the most hazardous configuration and deserve the most careful light.

Two-way switching is not a luxury here

A stair light that can only be operated from one end guarantees that somebody will use the stair in the dark rather than walk back up to switch it on.

Switches at both ends of every flight is the traditional arrangement, and automatic sensors achieve the same result without a decision being required.

Low-level night lighting, bright enough to show the edges and dim enough not to wake anyone, covers the case the main circuit handles badly.

Maintenance access is part of the design

A fitting hung in a stairwell void may be several metres above the flight below, and changing a lamp there requires equipment most households do not own.

Choosing positions reachable from a landing, or fittings with very long service lives, prevents a light that is technically excellent and practically never replaced.