Why Are My Lights Flickering in My San Francisco Home? (Common Causes + Fixes)

Flickering lights are one of those problems that can feel minor—until they don’t. Maybe your kitchen pendants “pulse” when the dishwasher kicks on. Maybe a hallway LED blinks like it’s trying to send Morse code. Or maybe the whole house does a brief dim-and-bright routine that makes you wonder whether you’re imagining it.

In San Francisco, flickering is especially common because the housing stock is a mix of old and new: Victorians and Edwardians with decades of “creative” wiring changes, condos with shared electrical rooms, additions and ADUs, and modern high-draw appliances layered onto systems that were never designed for them. Add coastal moisture, salty air, and occasional utility disturbances, and you’ve got plenty of reasons for lights to act up.

The good news: many causes are simple and inexpensive. The not-so-good news: some flicker patterns can point to loose connections or neutral issues that deserve immediate attention.

This long guide walks you through what flickering actually means, how to narrow down the cause, what you can safely check yourself, and when it’s time to call a licensed electrician.

What “Flicker” Really Is (And Why It Happens)

The basic idea: your lights react to voltage and signal quality

Most residential lighting is designed to operate at a fairly steady voltage. When the voltage drops briefly, lights dim. When it rises, lights brighten. When the current is interrupted—even for a split second—some lamps visibly flicker or blink.

But “flicker” isn’t one single phenomenon. It’s a family of symptoms that can come from very different sources:

• Voltage drop (sag): Often caused by large loads turning on (HVAC, refrigerator, microwave, EV charger).
• Loose connection: Creates intermittent resistance and arcing; can cause rapid flicker, random brightness changes, or blinking.
• Incompatible dimmer + LED driver: A common cause of pulsing, strobing, or shimmer.
• Utility-side disturbance: Can affect multiple homes at once, or show up during storms/wind.
• Neutral problems: Sometimes the scariest category—can cause lights to brighten in one area while dimming in another.

Incandescent vs LED vs smart bulbs: why the same circuit behaves differently

• Incandescent bulbs are basically little heaters. They tolerate small voltage changes smoothly; you might see mild dimming.
• LED bulbs use drivers (mini power supplies). Some drivers exaggerate small fluctuations into visible flicker, especially cheap LEDs.
• Smart bulbs add electronics and often a radio, plus they can dislike certain dimmers or noisy power.
• Fluorescent/CFL can flicker due to aging ballasts or low temperatures, but many SF homes have moved away from them.

Bottom line: flicker isn’t always a sign of danger—but it’s always a sign to pay attention.

Safety First: When Flickering Is an Emergency

Before you troubleshoot, do a quick safety triage. If you notice any of the following, stop experimenting and call a professional:

Call an electrician ASAP if you see:

• A burning smell near a switch, outlet, or fixture
• Heat on a switch plate or outlet cover (warm is not “normal”)
• Buzzing/crackling from a switch, dimmer, outlet, or electrical panel
• Discoloration (brown/black marks) around outlets, switches, or ceiling can lights
• Flicker affecting multiple rooms plus unusual behavior (appliances acting odd, electronics resetting)
• Flicker that gets worse with wind/rain, or coincides with sparking at the service mast (outside)

If lights brighten in one area while dimming in another

That pattern can point to a neutral issue (more on this later). Neutral problems can create overvoltage on one “leg” of a split-phase system, which is hard on electronics and can be hazardous.

Step One: Describe the Flicker Like a Technician Would

The fastest way to solve flicker is to treat it like a pattern-matching problem. Here are the questions that narrow the cause dramatically.

Is it one light, one room, or the whole house?

• One bulb/fixture → often a lamp issue, loose bulb, failing LED driver, loose fixture connection
• One room / one circuit → likely wiring, a loose connection, dimmer issue, or overload on that circuit
• Multiple rooms / whole house → panel, service, or utility-side issue is more likely

Is it random, rhythmic, or load-related?

• Random flicker (no obvious trigger) often points to a loose connection or failing component.
• Rhythmic pulsing is commonly dimmer/LED-driver interaction.
• Happens when something turns on suggests voltage drop or inrush current.

Is it a “blink off” or a “dip in brightness”?

• Blink off/on: interruption, loose connection, smart bulb reset, failing switch/dimmer.
• Dip in brightness: voltage sag, load start-up, undersized circuit, long wiring run.

Does it happen at certain times of day?

If it’s more common in the evening, it could correlate with neighborhood load, EV charging, heat pumps, or older utility gear working harder. Not a diagnosis, but a clue.

Quick Homeowner Checks (Safe and Worth Doing)

These steps won’t fix every scenario, but they prevent you from paying for a service call that ends with “the bulb was loose.”

1) Swap the bulb (and don’t assume “new” means “good”)

Try a known-quality LED bulb from a reputable brand. Cheap LEDs are famous for visible flicker even on stable power.

Tip: If only one bulb in a multi-bulb fixture flickers, move that bulb to a different socket and see if the problem follows the bulb or stays with the socket.

2) Tighten the bulb—gently

A slightly loose base can cause micro-arcing. Don’t crank it down like a jar lid; snug is enough.

3) Check if the light is on a dimmer

If yes, your top suspects become:

• dimmer not rated for LEDs
• LED bulbs not dimmable
• smart bulb installed on a dimmer
• dimmer load too low (some dimmers need a minimum)

4) Remove the dimmer from the equation (as a test)

If it’s safe and you know what you’re doing, set the dimmer to full brightness and see if the flicker stops. Many LED compatibility issues are worst at low dim levels.

If you’re not comfortable touching wiring: don’t. A simple test is to replace the dimmed bulb temporarily with an incandescent (if available) and see if behavior changes.

5) Notice what else is running when flicker happens

Write it down: heater, microwave, toaster oven, hair dryer, portable AC, laundry, dishwasher, EV charging, etc. The combination is often the clue.

6) Try a different outlet for sensitive lamps

Plug-in lamps flickering can be caused by a loose outlet connection. Try another outlet on a different circuit.

A Technician’s Cheat Sheet: Symptoms, Likely Causes, What to Do

Common Causes in San Francisco Homes (And the Fixes That Actually Work)

1) Loose Bulb, Worn Socket, or Failing Fixture Connection

What it looks like: One fixture flickers when bumped, or flickers intermittently with no clear trigger.

Why it happens:
Sockets wear. Fixture wiring loosens over years of heat cycles. In older homes, you’ll also see brittle insulation and older splices inside ceiling boxes.

Fix:

• Replace the bulb (first step).
• If it persists: inspect the socket and fixture wiring, tighten terminals properly, replace the fixture if it’s aging or damaged.

Why you shouldn’t ignore it:
Loose connections can arc. Arcing is heat.

2) Dimmer Switch + LED Compatibility Problems (The #1 “Modern” Flicker)

This is probably the most common “nothing is actually broken, but it looks broken” scenario.

What it looks like:

• shimmer at low brightness
• pulsing at medium levels
• strobe when dimmed
• flicker only on certain dimmer settings

Why it happens:
Many older dimmers were built for incandescent loads. LED bulbs use electronic drivers that don’t play nicely with every dimmer design. Some dimmers also need a minimum load to regulate properly, and a few LED bulbs don’t actually dim well even if the box says they do.

Fix options:

• Install a modern LED-rated dimmer designed for low loads.
• Use bulbs listed as compatible with that dimmer.
• Avoid mixing bulb types on the same dimmer.
• If using smart bulbs: avoid dimmers (smart bulbs want constant power).

Pro detail that saves time:
Some flicker is caused by a dimmer’s “trim” range. Many quality dimmers let you set a minimum brightness threshold so the LEDs don’t enter their unstable range.

3) Overloaded Circuits and Shared Loads (Especially in Kitchens)

What it looks like:
Lights dip when the microwave, toaster oven, espresso machine, or air fryer runs. It’s common in older SF kitchens that were upgraded cosmetically, but not electrically.

Why it happens:
A lot of older homes were wired when the biggest load was a radio and a couple lamps. Modern kitchens are different. If lighting and outlets share a circuit, voltage sag becomes visible.

Fix:

• Add dedicated circuits for high-draw appliances.
• Separate lighting from receptacle circuits where appropriate.
• Perform a load assessment if you’re adding multiple big appliances or an EV charger.

Good to know:
“Overloaded” doesn’t always mean “breaker trips.” You can be running near the edge of a circuit’s comfortable capacity without crossing the trip threshold, and lights can still tell the story.

4) Voltage Drop From Inrush Current (Motors and Compressors)

What it looks like:
A quick dim when the refrigerator compressor kicks on, when a heat pump starts, or when a portable AC cycles.

Why it happens:
Motors draw a large inrush current at startup. If the wiring run is long, connections are marginal, or the circuit is shared with lighting, you’ll see a momentary sag.

Fix:

• Put motor/compressor loads on a dedicated circuit.
• Check and tighten connections (panel, junctions).
• Upgrade undersized or aging components.

When it’s normal:
A tiny, occasional dip can be normal. Repeated or worsening dips, or dips across many circuits, deserve attention.

5) Loose Connections in Switches, Outlets, or Junction Boxes (A Real SF Classic)

What it looks like:
Random flicker in a room. Sometimes a faint buzz. Sometimes a switch plate is warm.

Why it happens:
Loose terminals create resistance. Resistance creates heat. Heat loosens things more. It’s a bad loop.

Older homes often have multiple layers of electrical work over the decades. You might have:

• backstabbed outlets (a common failure point)
• crowded junction boxes
• aging wire nuts
• splices hidden behind remodeled walls
• old switch legs and shared neutrals

Fix:
A licensed electrician will:

• identify the circuit
• inspect every device and junction on it
• remake suspect connections with proper torque and connectors
• replace damaged devices

Urgency: High.
Loose connections can arc. Arcing can ignite nearby materials—especially in older framing and dusty cavities.

6) Panel and Breaker Issues (Including Neutral Bar Problems)

What it looks like:
Flicker on multiple circuits, occasional resets of electronics, unexplained dimming in different rooms.

Why it happens:
Inside the panel, connections matter just as much as at switches. Loose neutrals, corrosion, tired breakers, or damaged bus bars can cause intermittent voltage behavior.

Fix:

• Torque-check critical connections (performed safely with power isolated when needed).
• Replace failing breakers.
• Address corrosion, water intrusion, or overheating signs.
• In some cases: panel repair or replacement.

San Francisco context:
Coastal moisture plus older enclosures can accelerate corrosion. Panels in garages and basements take extra abuse.

7) The Big One: Service Neutral Problems (Why “Bright + Dim” Is a Red Flag)

Most SF homes have split-phase 120/240V service. Two “hot” legs share a neutral. When the neutral connection becomes loose or compromised—anywhere from your panel to the utility connection—voltages can shift unpredictably depending on loads in the house.

What it looks like:

• lights get unusually bright in one area while dimming in another
• flicker feels “house-wide,” not tied to one room
• sensitive electronics misbehave

Why it’s serious:
Overvoltage on one leg can damage electronics and create overheating at connections.

Fix:
This isn’t a DIY situation. It may involve:

• securing neutral connections in the panel or meter base
• checking service conductors
• coordinating with the utility if the issue is upstream

Bottom line: If you suspect a neutral issue, treat it as urgent.

8) Utility-Side Voltage Fluctuations (Yes, Sometimes It’s Not Your House)

What it looks like:
Whole-house flicker that happens at the same time as neighbors, or correlates with wind or storms.

Why it happens:
Utility lines can experience momentary disturbances from switching operations, wind-caused contact, tree branches, or aging infrastructure.

How to test the “is it just me?” question:

• Ask a neighbor if they noticed it.
• Check if streetlights flickered.
• Note the time and frequency.

What you can do:

• If it’s rare, you may simply monitor.
• If frequent, document events and contact an electrician first to confirm your service is solid; then report to the utility with details.

9) Smart Home Gear and Power Quality Noise

What it looks like:
Smart bulbs or smart switches act flaky: blinking, disconnecting, resetting, flickering in patterns that don’t look like classic voltage sag.

Why it happens:

• Some smart devices are sensitive to minor power quality issues.
• Poor dimmer compatibility is common.
• Wi-Fi interruptions can look like “electrical” issues if the device’s firmware behaves oddly.
• Cheap drivers can create noise on the line and bother other lights.

Fix:

• Remove dimmers from smart bulbs.
• Use devices rated for the load type (LED, fan, etc.).
• If the issue is localized, check wiring integrity on that circuit.

10) Older Wiring Types and Past Remodel Surprises

San Francisco homes often come with history. Not all of it is charming.

Common contributors to flicker in older systems:

• Aging cloth insulation that cracks and leads to poor splices
• Mixed wiring eras (old branch circuits tied into new additions)
• Crowded boxes from multiple remodel layers
• Improper splices buried behind walls
• Aluminum branch wiring (less common in SF than some regions, but possible in certain eras/areas)
• Multi-wire branch circuits that were modified incorrectly (shared neutral problems on a smaller scale)

Fix:
A professional diagnosis matters here. Quick “patches” often create new problems.

How to Narrow It Down Like a Pro (A Step-by-Step Diagnostic Flow)

Step 1 — Identify the scope

• One fixture? Start with bulb/fixture/dimmer.
• One room? Focus on that circuit.
• Whole house? Think service/panel/utility.

Step 2 — Decide if it’s load-related

Try to trigger it:

• Turn on the microwave.
• Start the washer.
• Turn on a space heater.
• Begin EV charging (if applicable).

If you can reliably recreate the flicker with a specific load, you’re likely dealing with voltage sag, shared circuits, or inrush current.

Step 3 — Rule out dimmer/LED issues

• Test at full brightness.
• Swap in a known good LED.
• Check whether the bulb is dimmable.
• Consider replacing the dimmer with a known LED-compatible model.

Step 4 — Look for “loose connection” clues

Without opening anything:

• Is there buzzing?
• Is a switch warm?
• Does flicker worsen when the switch is touched?
• Any smell?

If yes, stop and call a professional.

Step 5 — If it’s bigger than one circuit, consider service/panel

Whole-house flicker, bright/dim shifts, or multiple circuits acting up usually warrants a deeper electrical evaluation.

What a Licensed Electrician Will Actually Do (So You Know What You’re Paying For)

A good service call isn’t guesswork. Here’s what a thorough diagnosis often includes:

Visual inspection and targeted questions

• When does it happen?
• Which rooms?
• Which devices were running?
• Any recent renovations, new appliances, or EV charging additions?

Circuit testing

• Measure voltage under load at key points
• Compare behavior across circuits
• Check for abnormal voltage drop

Connection integrity checks

• Inspect and re-terminate suspect devices (switches/outlets)
• Inspect junction boxes and splices where accessible
• Evaluate the panel: neutral bar, breakers, bus condition

Load assessment

• Identify heavy loads and how they’re distributed
• Confirm whether dedicated circuits are needed
• Consider whether the service size and panel capacity match the home’s current reality

If needed, coordination with the utility

If symptoms point upstream (service drop, meter base, utility neutral), the electrician can help confirm and coordinate next steps appropriately.

Fixes That Provide Real Long-Term Value (Not Just a Band-Aid)

1) Upgrade dimmers and standardize bulbs

If you have a house full of mismatched LEDs, different dimmer types, and a few bargain bulbs, you’re basically running a compatibility experiment.

A clean setup looks like:

• quality LED-rated dimmers where needed
• consistent, reputable dimmable LED bulbs on those dimmers
• no smart bulbs on dimmers

2) Add dedicated circuits for modern loads

This is the quiet hero of many “mystery flicker” cases—especially in kitchens, laundry areas, and garages.

3) Correct weak links in devices and splices

Replacing backstabbed outlets, worn switches, and tired connections is unglamorous work that pays off immediately.

4) Panel maintenance, repairs, or replacement when warranted

If the panel is showing signs of heat, corrosion, loose connections, or it’s simply undersized for today’s loads, addressing it isn’t just about flicker—it’s about reliability and safety.

5) Plan for electrification (heat pumps, induction, EV charging)

San Francisco homeowners are increasingly adding electrical loads as they modernize. If you’re stacking upgrades, do it strategically:

• load calculation
• circuit planning
• possible service upgrade (only when truly necessary)
• smart load management options where appropriate

Frequently Asked Questions

A Practical Wrap-Up: The Short Version You Can Use Today

If your lights flicker in a San Francisco home, the fastest path is:

1. Figure out the scope (one fixture vs one circuit vs whole house)
2. Rule out bulb/dimmer compatibility
3. Watch for load triggers (microwave, HVAC, EV charging)
4. Take loose-connection clues seriously (buzzing, warmth, smell)
5. If it’s widespread or “bright + dim,” treat it as urgent