Why Are My Lights Dimming?
Lights that dim when the AC starts, when the fridge kicks on, or randomly through the day — here's what each pattern means.
Lights that dim briefly when a big motor starts is often normal, especially in older homes with 100A service or long branch runs. Lights that dim steadily under load, dim in only part of the house, or dim in a pattern that inverts (one half brightens while the other dims) point to real problems — often a bad neutral or an undersized service.
Key details
- Brief dim on AC start: usually normal
- Steady dim under load: undersized service or wire
- Half-and-half dim/brighten: bad main neutral (dangerous)
- Random flicker: loose connection
- Whole-house dim: utility drop or main issue
- LED-only dim: dimmer/driver incompatibility
The normal kind
Central AC compressors, well pumps, and large power tools all draw a starting current 4-6x their running current. A brief dim across the whole house or one circuit is inrush current and usually normal — especially on 100A services or long branch runs.
The upgrade-your-service kind
If lights are noticeably dimmer whenever the AC, oven, or dryer is running, you're likely at the edge of your service capacity. A modern home with EV, heat pump, or induction range on a 100A service will feel it. Upgrading to 200A usually solves this along with providing headroom for future loads.
The call-immediately kind
Lights on one side of the house dim while lights on the other side brighten — a classic bad-neutral symptom. This is dangerous: voltage on one leg climbs above 120V and appliances start dying. Kill the main and call for emergency service.
Why Are My Lights Dimming? — FAQs
Services that pair with this
Local coverage
Talk to a licensed electrician today.
Same-day quotes. Same-week scheduling. Free written estimates.