How to Choose Architectural LED Lighting for a Space

There are a lot of fixtures to choose from and most of the advice on choosing them starts at the catalog. That is backwards. The fixture is the last decision, not the first. Below is the order we work in on a real project, eight decisions long, with a living room carried through as the example so the numbers are concrete. The same sequence works for a kitchen, an office or a shop.

1. What happens in the room, and where

Write down the activities, then mark on the plan where each one happens. Not just reading, but reading in the armchair by the window. Not just entertaining, but eight people on the two sofas and the low table between them. Lighting is aimed at places, and you cannot aim it until the places are named.

The example: a 16 by 20 foot living room, 9 foot ceiling. Two sofas facing each other across a coffee table. A reading chair in one corner. A 12 foot wall of built-in shelves with a fireplace in the middle. A large painting on the opposite wall. One long window wall.

2. Target light levels for each

Light level is measured in footcandles, lumens per square foot. For a living room the general level is low, 5 to 15 footcandles across the floor, because the room is meant to feel calm. Reading wants 30 or more at the page. Art and shelves want to be two to five times brighter than the wall around them, which is a ratio rather than a number.

Writing the targets down does two things. It stops the room being over-lit, which is the commonest fault in residential schemes. And it gives you something to check the finished layout against, with a calculation before installation or a light meter after.

3. Layers before fixtures

Every room gets three layers, and each is a separate decision.

• General: enough light to move around and see faces. In the example, a soft fill over the seating area rather than an even wash over the whole floor.
• Task: light where hands or eyes work. The reading chair, a desk, a counter.
• Accent: light on the things worth looking at. The painting, the shelves, the fireplace stone.

A room with only the first layer is the one everyone recognizes as flat. A room with only accent is a gallery. All three, on separate dimmers, is a room that works at breakfast and at ten at night.

4. Fixture families for each layer

Now the catalog, but by layer.

General: fixed recessed downlights with a wide beam, 50 to 80 degrees, placed around the seating rather than on a grid. In the example, four 3 inch downlights at the corners of the seating group, about 6 feet apart.

Task: an adjustable downlight with a 25 degree beam over the reading chair, aimed at the page rather than the top of the reader's head, which means placing it about 2 feet in front of the chair and tilting it back.

Accent: two adjustable downlights aimed at the painting from about 3 feet off the wall, which gives a 30 degree aiming angle from a 9 foot ceiling and keeps reflections out of the viewer's eyes. LED strip in a profile along the front of each shelf for the built-ins. A 15 degree spot on the fireplace stone.

That is eleven small apertures and a run of strip in a room that would conventionally get nine downlights on a grid. It is not more fixtures; it is fixtures doing different jobs.

5. Color temperature and color rendering

One color temperature for the whole room, and usually for every room that can be seen from it. 2700K for living spaces is the traditional answer and still the right one for most houses; 3000K if the room is bright and modern or opens onto a kitchen at 3000K. Do not mix them in one sightline. If evening use matters, a dim to warm engine drops from 3000K to 1800K as the fixture dims, which gives the candlelit end of the range without a second set of fixtures.

Color rendering: 90 CRI is the floor, 95 or better where there is timber, stone, fabric or art under the light. In the example that is the whole room. Ask for the R9 value too, since it is the red content that separates a good chip from an adequate one, and cheap chips score well on CRI while failing R9.

6. Beam angle and aperture

Beam angle is the spread of the light. A useful shortcut: the diameter of the pool on a surface is roughly twice the distance from the fixture multiplied by the tangent of half the beam angle. From 9 feet, a 15 degree beam makes a pool about 2.4 feet across, a 25 degree beam about 4 feet, a 50 degree beam about 8.4 feet. Narrow beams for objects, wide beams for floors.

Aperture is how much of the fixture you see. A 3 inch cutout is the workhorse. A 1 inch or a pinhole where the ceiling should stay unbroken. Trimless where the ceiling is plaster and the budget allows the plasterer's time; micro-flange where it does not.

7. Control

Every layer on its own dimmer, at minimum. That is three circuits in the example, and it is the cheapest decision in the whole project to make at rough-in and the most expensive to make afterward. The driver has to match the dimmer: TRIAC for an ordinary wall dimmer, 0-10V or DALI-2 for a control system, Casambi for wireless control from a phone without a control system. Flicker and a poor low end almost always come from a driver and dimmer that were not chosen together.

8. Housing, rating and listing

The unglamorous decisions that stop the project on site if they are wrong. An IC rated housing wherever insulation will touch the fixture, which is most ceilings under a roof. IP44 in a bathroom, IP65 in a shower or outside. ETL or cETL listing for North America. And an IES file for each fixture, so the layout can be checked by calculation before anyone cuts a hole.

The mistakes this sequence avoids

• A grid of downlights centered on the room, lighting the floor and nothing else
• Warm and cool color temperatures visible from the same seat
• No task light where people actually read or work
• Accent fixtures placed too close to the wall, so the painting gets a hot spot at the top and shadow below
• One circuit for everything, so the room is either on or off
• A driver that does not match the dimmer

If you would rather not work through it alone

This is the process our lighting design service runs, on a plan rather than a paragraph. Send us the drawings and we will return the layout with calculated light levels, the fixture schedule and the control zoning, specified against the fixtures we make. It is included when the project goes ahead with our fixtures.