Lighting Design

I've been holding off thinking about lighting, because it's fun--sort of a reward for doing the less-fun design. The actual design is still in the future, but Peggy sent a guide for Residential Lighting, developed by the California Lighting Technology Center at UC Davis. In addition to specific recommendations, the guide explains the intent of laws like California's Title 24. I don't think Washington is as rigorous, yet.

The basic rule is that you can have low efficacy (low light output per watt used) if you provide special switches or high efficacy ambient lighting. You can buy inefficient lighting credits, sort of.

One thing that bothered me about California's standard is that they want "vacancy" switches that turn the lights off when no one is in the room. I have no problem with switches that both turn off and turn on the lights based on motion detection, but California insists that the switches must turn off only. No "occupancy" switches; only "vacancy." They recommend ultrasonic instead of the old passive IR sensors to avoid turning the lights out on someone hiding from the sensor.

Also, they don't seem to like fixtures that are capable of using an incandescent lamp--so, no cheap CFLs. No cheap fixtures, for that matter. They want CFLs with a GU-24 base, like the low-voltage halogens we used to have in the kid's rooms. Track lighting is bad because you can switch out the lights.

They also encourage "layers of light"--ambient, task, and accent lighting. They like dimmers and 3-way switches, particularly for hallways. Since they like dimmers, they like lighting control systems that let users choose more dramatic, dimmer, lighting. They like low and high setting LED lights for front porches. It's on dimly until the sensor detects motion, then it brightens.

The guide explains the measurements: Lumens is the light output. Lumens/watts is the efficacy. Incandescent is low-, LED is high-efficacy.

Color temperature (CCT) is how warm/cold the light looks, and CRI is the "color rendition index," which shows how truly colors appear in the light.  CCT above 4,000K are too cool, but the guide stresses that keeping CCT consistent is the important thing. I agree.

CRI of 100 is perfect, 80 is not very accurate. The guide says aim for a CRI of 90 or better.

Kitchen: Ambient lighting--CFL (compact fluorescent lamps) downlights. Task lighting--especially at the sink (with a separate switch). Watch out for countertop glare. Under cabinet lights are calculated as part of the total--at least 50% must be high-efficacy. High-efficacy lights must be switched separately from low-efficacy. Their example shows a square kitchen, about 100 SF, 8,508 lumens.

Bathroom: Each must have at least one high-efficacy light. Any low-efficacy fixtures must have a vacancy switch. Any fans must be switched separately from lights. The guide shows as an example: a ceiling light (GU-24 base LED) and a vertical bath bar (dedicated LED) on either side of the mirror on one switch--45W total. A GU-24 base LED downlight over the shower--12W--on a separate switch. 2,700 lumens in a small 3/4 bath (not counting the shower downlight, another 804).

Garage: Lights in the door opener are okay, but they have to turn off automatically (as they all do). They show 3 "linear surface mount" (dedicated LED) fixtures--154W total, on a switch with a VS (vacancy sensor). The 2-car garage seems to get 11,858 lumens.

The guide seems to avoid suggesting lumens--the examples talk efficacy, but you have to reverse engineer lumens yourself. Their kitchen example has about 142 lumens/SF on 3 switches (main, island, and task). Their bath is 83.5 lumens/SF on 2 switches (main, shower). And the garage is 30 lumens/SF on one VS switch. Their living room example has three switches, 57 lumens/SF.

Next step: WAC 51-11R, the Washington State Energy Code, Residential Provisions.