Lighting, Switching & Automation

Table 1 maps the parts to the three components. Subsections that cover one component carry an Applies to tag. An Informs tag marks the subsections behind each decision above.

1 · Light: quantities, layers, daylight and color

Bottom line. What a room needs is illuminance on its surfaces and a color and glare quality suited to the task; Title 24 regulates the efficacy of sources and the controls, not the light delivered, so adequacy and compliance are separate checks.

Illuminance is lumens per area at the surface; the code does not regulate it

LightingWiringControls

Informs D1

A lumen is a quantity of visible light leaving a source; a footcandle is one lumen per square foot arriving at a surface (10.76 lux). Fixtures are rated in lumens; tasks need footcandles, and the conversion depends on the room (Part 2). Correlated color temperature (CCT, kelvin) places white light from warm (2700 K) to cool (5000 K); color rendering (CRI R_a, and R9 for saturated red) scores how faithfully colors appear. The Energy Code's JA8 sets a floor for a high-efficacy source, 45 lm/W, CRI 90 with R9 50, dimming to 10% and low flicker, and caps CCT at 4000 K for inseparable LED light engines and GU24 lamps and at 3000 K for other replaceable lamps such as screw-base, MR16 and GU10. It says nothing about how much light a room receives. Table 2 gives typical residential targets.

Typical ranges after IES RP-11 residential guidance; older eyes need about twice the light of younger ones for the same task.

Layers are separate fixtures for separate targets, controlled separately

Informs D1 D3

Ambient light fills the room at an orientation level; task light raises one surface to its working level; accent light picks out a surface or object. Sizing one source for the brightest task over-lights the room the rest of the time, and dimming one ambient circuit for evening also dims the counter. Each layer therefore gets its own circuit or control channel, which is also what Title 24 encodes in its separate switching of under-cabinet lighting (Figure 1).

Useful daylight reaches about 1.5–2 window-head heights into a room, typically

LightingWiringControls

Informs D1

DF average daylight factor, % · T_vis visible transmittance of the glazing · A_w glazed area, sf · θ visible sky angle in the vertical plane through the window, degrees (90 unobstructed) · A_total all room surfaces, sf · R mean surface reflectance

the share of outdoor daylight arriving indoors rises with glass area, its clarity and the sky the window can see, and falls with the room's size and darkness.

Daylight useful for tasks penetrates about 1.5 times the window head height, and up to twice where the ceiling and upper walls are light; with an 80 in head that is 10–13 ft. The reference bedroom with one 3 × 5 ft window at T_vis 0.6 has an average daylight factor near 1.3% with an open view, taking θ as 72° rather than 90° to allow for ground-level clutter. A two-story neighbor 10 ft away cuts the visible sky to about 32° at a ground-floor window and 55° at a second-floor window, giving 0.6% and 1.0% (Figure 2). Typical targets (BRE, BS 8206-2) are about 1% for a bedroom, 1.5% for a living room and 2% for a kitchen. Glazing choice sets T_vis (Windows & Doors · Visible transmittance); the obstruction sets θ, and on a narrow side yard it governs.

Glare depends on source brightness against its background, not on lumens

LightingWiringControls

Informs D1 D2

A small bright source in a dim field glares where a larger diffuse source of the same output does not. Downlights shield their source with a cutoff angle; a deep regressed trim keeps the emitter out of view at normal sight lines, while a flush wafer puts it in view from across the room. Contrast between a bright window and a dark wall is a daytime glare source that electric light on the wall beside the window reduces. Warmer CCT in the evening (2700 K and lower, including warm-dim sources that shift as they dim) reduces the short-wavelength light associated with alertness; cooler CCT suits daytime tasks.

2 · Sizing: the lumen method

Bottom line. Lumens needed are illuminance times area divided by the share of fixture output that reaches the work plane after the room absorbs some and the fixture ages; the share falls as the room gets smaller, taller or darker.

Lumens needed are illuminance times area over utilization and light loss

LightingWiringControls

Informs D1

Φ fixture lumens needed · E target illuminance, fc · A floor area, sf · CU coefficient of utilization, from the fixture and the room cavity ratio RCR · LLF light loss factor, about 0.85 for LED · h height from work plane to fixture, ft

deliver the target over the area, then divide by the share of light that reaches the work plane, which shrinks as the room's walls become a larger part of what the light hits.

The reference bedroom, 12 × 12 ft with an 8 ft ceiling and a 2.5 ft work plane, has an RCR of 4.6 and, for a wide-beam downlight with light surfaces, a CU near 0.57 (Figure 3). Ten footcandles of ambient light take about 3,000 lm, four 750 lm downlights at a spacing inside the 1.0–1.5 times mounting height that wide-beam downlights typically allow. A 14 × 14 ft kitchen at 20 fc takes about 7,200 lm of ambient light, and under-cabinet strips for 50 fc on 40 sf of counter about 2,900 lm, 8 ft of a 350 lm/ft strip.

Table 3 gives the effect of ceiling height on the reference bedroom.

Dark finishes lower CU further: from 80/50/20 to 70/30/20 reflectances, CU falls by roughly 15–25% at these ratios (typical).

LED lighting draws a fifth to a tenth or less of the code's general lighting load

Informs D1 D3

The power a lit room draws is the lumens divided by efficacy: at 90 lm/W the reference bedroom's ambient layer draws about 0.23 W/sf, the kitchen's general light 0.41, and the kitchen with its counter task layer 0.57 (Figure 4). The NEC's 3 VA/sf general lighting load (Electrical · Load stack) is a service-sizing convention covering lighting and general receptacles, five to thirteen times the lighting layers. A whole LED house at about 0.5 W/sf, the kitchen figure above spread over every room as an upper value, connects a sixth of it.

3 · Ceiling fixtures: recessed, canless and surface

Bottom line. A ceiling fixture is either a hole in the ceiling or a box on it; a hole is charged to the ceiling's air barrier, its acoustic decoupling and, where the ceiling separates a garage from rooms above, the fire separation.

A recessed fixture is charged to up to three ledgers, the third in a garage ceiling below rooms

Informs D2

Every recessed luminaire is labeled airtight (no more than 2.0 cfm at 75 Pa under ASTM E283), sealed to the ceiling with a gasket or caulk, has no screw-base socket, uses a JA8 source tested for elevated temperature and meets 410.116; in an insulated ceiling, 410.116 makes it IC-rated unless 3 in of clearance to insulation is kept (Insulation · Ceiling leakage). In a decoupled ceiling every fixture is an opening and, if its housing or box touches framing, a rigid bridge across the isolation (Soundproofing · Flanking). The ⅝ in Type X ceiling of a garage below habitable rooms is a separation rather than a rated assembly: penetrations are sealed with an approved material (CRC R302.5.3 and R302.11), and some building departments ask for a protective enclosure over recessed housings (Figure 5).

Table 4 compares the ambient fixture types.

4 · Circuits, protection and the switch box

Bottom line. The code's lighting load sets a minimum circuit capacity that LED layouts rarely approach; circuits are then set by protection, layers and control, and the switch box needs a neutral and room for an electronic control.

Lighting circuits follow layout and control, not load

LightingWiringControls

Informs D3

The general lighting load in the service calculation (220.41, 3 VA/sf, 6,900 VA in the 2,300 sf reference house) and the receptacle circuits and breaker protection are treated in Electrical · Load stack; an LED house uses a small part of that capacity. What lighting adds is placement: 210.70 requires a switched lighting outlet in every habitable room, bathroom, hallway, stairway, garage and at outdoor entrances, with switches at each level of a stair with six or more risers, and allows a switched receptacle instead in habitable rooms other than kitchens and bathrooms. Lighting circuits are then divided by floor and zone so one fault does not darken a floor, and by layer where a relay or dimmer channel controls it. Where a remodel modifies, replaces or extends branch-circuit wiring in the areas that need arc-fault protection, the circuit takes it, except an extension of 6 ft or less that adds no outlet or device (210.12(D)). California dwellings carry no emergency or egress lighting requirement.

A neutral and a deep box keep every switch location open to electronic control

Informs D3 D5

An electronic switch needs standby power. Without a neutral it draws it through the load, which makes LED loads glow or flicker when off, or through the equipment grounding conductor. 404.2(C) requires the grounded conductor at switch locations controlling lighting in habitable rooms, bathrooms, hallways and stairways, except where a raceway or an accessible box allows it to be added later, the switch has an integral enclosure, the lighting is automatic only, or the switch controls a receptacle (Figure 6); in new finished walls these exceptions rarely apply. Where several switches control the same load and the whole room is visible from them, the neutral is needed at only one location. The 404.2(C) exception for replacement switches where a neutral cannot be added without removing finishes permits electronic switches that put current on the grounding conductor (404.22), marked for replacement use, at no more than five on a branch circuit and 25 on a feeder.

Electronic dimmers and keypads are deeper than toggles and shed heat; a 20 in³ single-gang box that holds a toggle and its conductors may not hold a smart dimmer and the same conductors under the box-fill rule (314.16), and multigang dimmers derate when side fins are removed. A deep box and a neutral cost little in an open wall.

Low-voltage LED circuits trade conductor size against voltage

Informs D3 D4

K 12.9 Ω·cmil/ft for copper · P load, W · V supply voltage · L one-way length, ft · CM conductor area, circular mils

at a fixed power, halving the voltage doubles the current and quadruples the percentage drop.

A 16 ft run of 4.4 W/ft tape (70 W) fed over 20 ft of 18 AWG drops 3.9% at 24 V and 16% at 12 V, enough at 12 V to dim and shift color at the far end (Figure 7). Many tape drivers are Class 2 sources, limited to about 60 W at 12 V (5 A) and 96–100 W at 24 V, so the 12 V case needs two drivers or a non-Class 2 supply; Class 2 wiring is separated from line-voltage conductors in boxes and raceways (725.136). The driver needs an accessible location: a box, a cabinet void or a closet, not a closed ceiling.

5 · Dimming and flicker

Bottom line. An LED driver, not the lamp, decides how a dimmer behaves; the dimmer and driver have to be designed for each other, and the low end of the range is where mismatches show.

Phase-cut, 0–10 V and digital dimming differ in what the wiring carries

Informs D4

Forward phase-cut (leading-edge) dimmers chop the start of each half cycle; reverse phase-cut (trailing-edge) dimmers chop the end, which suits electronic drivers and runs quieter. Both work over the two existing wires, and both depend on the driver: JA8 requires sources made for forward phase-cut dimmers to meet NEMA SSL 7A, the compatibility standard between the two. A 0–10 V driver takes a separate Class 2 control pair and dims smoothly to low levels; digital protocols (DALI, or wireless control inside the fixture) address each fixture. Table 5 compares them.

Flicker is modulation in light output, limited at full and partial output

LightingWiringControls

Informs D4

LED drivers smooth rectified line current to differing degrees; poor ones let light output follow the 120 Hz ripple. JA8 limits percent flicker to under 30% for frequencies below 200 Hz, tested at full output and at 20%, and limits audible noise to 24 dBA at 1 m. Flicker that meets the floor can still be visible in peripheral vision or as stroboscopic effects with moving objects; IEEE 1789 gives a stricter risk curve. Dimming deepens modulation in phase-cut systems, which is why the 20% test exists.

6 · Control architecture and the network

Bottom line. Control lives either in each wall box or in a central relay panel fed by home runs; the choice sets where a failure concentrates and what the rough-in carries, while the network decides whether controls keep working without the internet.

In-wall, relay panel and hybrid differ in rough-in, failure and reversibility

Informs D5 D3

An in-wall system replaces each switch with an electronic one on the normal branch wiring; a relay panel runs each controlled circuit home to an enclosure of relays and dimmers driven by low-voltage keypads; a hybrid centralizes some rooms and leaves the rest in the walls (Figure 8). Where the relay enclosure holds the branch breakers it is a subpanel with its own feeder; many are pass-through enclosures whose breakers stay in the main panel. Either way it needs working space and ventilation for dimmer heat (Electrical · Working space). Table 6 compares the three.

Radio links have a budget, and on paths through them low-E glass and metal lath spend most of it

LightingWiringControls

Informs D5

P_tx transmit power, dBm · FSPL free-space path loss, dB, with d in m and f in MHz · L material losses, dB · P_sensitivity receiver floor, dBm

a link works when what is sent, less what distance and the walls take, stays above what the receiver can hear, with room to spare for fading.

At 2.4 GHz (Zigbee, Thread, Wi-Fi) a path through interior walls keeps ample margin, while a path out through a low-E window keeps about 10 dB; 10–20 dB is a common target for a robust link (Figure 9). Wood and gypsum cost a few dB each regardless of their acoustic mass, so a wall's STC says nothing about its radio loss. Continuous metal does: a low-E coated window costs 25–40 dB, stucco on metal lath 10–25 dB, and foil-faced insulation, a foil radiant barrier or a metal duct run in the path tens of dB (typical), so links to outdoor sensors, cameras and devices beyond a foil-faced assembly run short of margin. Free-space loss understates indoor loss: inside a house the path-loss exponent is nearer 3 than 2, which typically costs another 10–20 dB at 10–15 m, so the margins here are upper values. At 908 MHz (Z-Wave in the US) every path gains about 9 dB. Mains-powered devices in Zigbee, Z-Wave and Thread meshes repeat the signal, so one device on the near side of an obstacle restores a link.

Table 7 compares the common networks.

Matter is an application layer that runs over Thread, Wi-Fi or Ethernet; it standardizes devices across makers.

7 · Energy, standby and load shedding

Bottom line. Controls draw power continuously and decide which loads run when power is short; shedding a load needs a switching device and a control path to it, and where the device sits away from the panel the path is placed while the walls are open.

Load shedding is a switching device and a control path per load

Informs D6

A storage inverter in backup runs one large load at a time (Solar & Battery · Continuous rating), and an energy management system can hold a service below its rating by limiting loads (Electrical · EMS setpoint). Both act on the same loads, the charger, supplementary heat, dryer and water heater element, and both need, for each load, a device that can interrupt it (a contactor, a controllable breaker, the charger's own current limit, or the appliance's demand-response input) and a path for the signal: a control conductor or a reliable radio link (Figure 10). The range is usually left to the occupant. How a shed device behaves when its controller fails is part of the EMS listing under Article 750. Table 8 lists the reference loads.

Standby power of controls is continuous

LightingWiringControls

Informs D5 D6

Each electronic switch, dimmer or sensor draws 0.3–0.8 W around the clock, typical. Forty devices draw 105–280 kWh a year, and in an outage the same 12–32 W comes from the battery for every hour of backup (Table 9). Hubs, bridges and network equipment add their own.

8 · Code, permits and documentation

Which codes apply

The 2025 Energy Code (Title 24 Part 6, §150.0(k) and Joint Appendix JA8) governs residential lighting efficacy and controls, and the 2025 California Electrical Code (the 2023 NEC) governs circuits, boxes and devices, both from 1 January 2026. In a remodel only lighting work done under the permit must comply: replacing or relocating a fixture or replacing a manual control brings that fixture or control under the current requirements, while changing a lamp does not. A recessed screw-base fixture may stay where a JA8 trim kit or lamp is used. Figure 11 draws the triggers; Table 10 lists the provisions.

Permits and documentation

An electrical permit covers new circuits, boxes and fixtures. The Energy Code's lighting requirements are documented on the installation certificate (CF2R-LTG-01, or the alteration form where allowed), which is on site before final; mandatory notes go on the plans. The inspector sees boxes, neutrals, AFCI and GFCI devices and box fill at rough-in, and at final the JA8 markings, IC-AT ratings and the controls by room. No code selects a protocol, a platform or an architecture.

Where it goes wrong

1. Fixtures counted instead of lumens sized. A tall or dark room with the usual downlight count is under-lit by a fifth or more (Part 2).
2. One circuit for all layers in a room. The task layer then dims with the ambient, and Title 24's separate under-cabinet switching is missed (Part 1).
3. Recessed housings in a decoupled ceiling. An airtight rating addresses air leakage, not the rigid bridge across the isolation (Part 3).
4. Unsealed penetrations in the garage ceiling below bedrooms, which open the required separation (Part 3).
5. No neutral, or a shallow box, at a switch. The first electronic control then opens the wall (Part 4).
6. 12 V tape on long feeds or on one Class 2 driver past its limit, which dims and shifts color at the far end (Part 4).
7. Drivers in closed ceilings. A driver is a replaceable part and needs an accessible location (Part 4).
8. Phase-cut dimmers and drivers not designed for each other, which flicker or drop out at the low end (Part 5).
9. A relay panel counted as free panel space. It needs a feeder, spaces and its own working clearance (Part 6).
10. Outdoor sensors behind low-E glass, stucco on lath or foil-faced insulation with no repeating device on the near side (Part 6).
11. A shed list decided at commissioning, when a control conductor to a load away from the panel can no longer be pulled (Part 7).
12. Controls that stop working without the internet in a house relying on them for backup shedding (Part 6, Part 7).

Reference

Glossary

CCT

Correlated color temperature, kelvin: the warmth or coolness of white light.

CRI, R9

Color rendering index and its saturated-red component.

CU

Coefficient of utilization: share of a fixture's lumens reaching the work plane.

Daylight factor

Indoor illuminance as a percentage of simultaneous outdoor illuminance under an overcast sky.

IC, airtight

Recessed housing rated for insulation contact; labeled airtight to ASTM E283.

JA8

Title 24 Joint Appendix 8: qualification of high-efficacy light sources.

LLF

Light loss factor: output retained after aging and dirt.

Percent flicker

Modulation depth of light output over a cycle, (max − min) ÷ (max + min).

RCR

Room cavity ratio: 5 × cavity height × perimeter ÷ area.

Relay panel

An enclosure of relays and dimmers switching home-run circuits on commands from keypads or a controller.

Visible sky angle

Angle in the vertical plane through a window between the obstruction's top and the window's view up, in degrees.

Formula sheet

Room size and the lumens it needs

Wide-beam downlights, 80/50/20 reflectances, LLF 0.85, work plane 2.5 ft.

Table 11 extends the reference room to other sizes.

Figure color legend

Red: deficient, or fails the stated criterionAmber: marginal or conditionalGreen: meets the criterionGray: existing or baselineTeal: neutral quantity, reference line or annotation; never a grade

In Figure 10 amber marks loads shed during backup, a conditional state.

Sources

• California Energy Commission, 2025 residential lighting mandatory measures (as published by the City of Roseville, 1 January 2026): §150.0(k)1–3, recessed downlights, blank boxes, alterations, CF2R-LTG; LightNOW, CA 2025 single-family residential energy code lighting changes (2025).
• Energy Code Ace, JA8.4 Qualification Requirements (2022 Reference Appendices): efficacy, CRI and R9, CCT, dimming, flicker, noise.
• NFPA 70 (2023): 210.8, 210.11, 210.12, 210.70, 220.41, 314.16, 404.2(C), 404.22, 410.116, 725.136, 750.30; EC&M, The apprentice's guide to Article 404.
• IES RP-11, residential lighting; IES Lighting Handbook lumen method; IEEE 1789 on flicker; NEMA SSL 7A.
• BRE average daylight factor method (Littlefair), class-typical.
• AGC Glass, Glass vs connectivity; Vitro, TD-151 — 25–40 dB attenuation through low-E coatings.
• CEC, 2022 Single-Family Lighting summary (recessed luminaire requirements); CRC R302.5.3 and R302.11 (garage separation penetrations); NEC Chapter 9 Table 11 (Class 2 limits).
• Companion guides: Electrical, Windows & Doors, Insulation, Soundproofing, Solar & Battery, Framing (set v2); Low-Voltage (set v2).

Set v2 draft 1a, 2026-10-23: Low-Voltage reference links to the set v2 guide. Draft 1, 2026-10-23: rewritten as a generic theory guide to spec set v2 from the v1 guide (archived). General lighting load cited at 220.41 (2023 NEC); the five-per-circuit limit restated as the 404.2(C) exception for replacement switches without a neutral; after review, 210.12(D), the recessed-luminaire rule, JA8 CCT caps, the garage separation, Class 2 limits and §150.0(k)2D corrected or added; JA8 and §150.0(k) checked against 2025 sources, with the blank-box rule and alteration triggers added; daylight, glare, lumen-method sensitivity, low-voltage drop, flicker and standby arithmetic added; RF budget corrected to the materials that matter (low-E glass, metal lath); house values moved to the House Project Guide. Values from one script.

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