Every house does this a little. The question is whether yours is doing it normally — or telling you something. Here's how we triage it.
The normal version
An air conditioner compressor needs four to six times its running current for the fraction of a second it takes to start spinning — a 20-amp-running compressor might gulp 80–100 amps momentarily. That inrush briefly pulls down voltage everywhere on the service, and incandescent and some LED lights show it as a quick, subtle dim. If your dimming is momentary, mild, happens only with big motor loads (AC, well pump, shop tools), and has been the same for years, it's physics, not a defect. An HVAC tech can add a hard-start kit to soften it further.
The patterns that mean something
Four patterns earn a professional look. Severe dimming — lights dropping dramatically, electronics rebooting — suggests the service or panel can't deliver the inrush, common on 100-amp services now carrying AC, an EV charger, and a modern kitchen. Worsening dimming — same AC, deeper dips than last summer — points at a connection loosening somewhere between the utility transformer and your breakers; connections fail progressively, and "it's getting worse" is exactly how that sounds. Dimming with small loads — microwave, kettle, hair dryer — shouldn't happen on a healthy service at all. And lights that brighten while others dim is a loose neutral — a genuine emergency that damages electronics and warrants an immediate call.
What we check and what fixes it
The diagnostic visit measures voltage drop at the panel while loads start, thermal-scans every connection, and checks the utility-side terminations. The fix matches the cause: re-torquing or repairing connections (cheap), moving the AC or other big loads to properly sized dedicated circuits, a 200-amp panel upgrade when the load calculation says the service is simply full, or a utility repair when the weak link is their splice at the pole — which we identify and they fix free.
If your dimming fits any of the four patterns — or it just bothers you — we'll diagnose it properly: 416-837-4038. For flicker unrelated to appliance starts, our flickering lights guide covers that separate family of causes.