It’s a common frustration: you turn on the air conditioner, start a steam shower, or fire up the shop compressor — and the lights in your home dim or flicker. While it might seem like just an annoyance, frequent dimming can also signal electrical strain that may shorten the life of your equipment or even pose safety concerns.
Fortunately, there are practical steps homeowners can take to reduce or eliminate this problem.
Why Do Lights Dim When Appliances Start?
Most often, light dimming is caused by inrush current — the surge of electricity a motor demands when it first starts. Unlike steady operation, motors require a much higher current to get spinning. Once they reach full speed, the current levels off.
Common culprits around the home include:
- Air conditioners and heat pumps – especially single-stage outdoor compressors that switch 100% on or off.
- Steam shower generators – powerful heating elements that pull heavy loads at startup.
- Air compressors – especially larger shop-style or industrial units.
The common theme is single-stage motors. They draw a large burst of current all at once, causing a temporary voltage drop in the home’s electrical system. The lights dim as a result.
Upgrade to Variable-Speed or ECM Motors
One of the best solutions is upgrading appliances to models with variable-speed compressors or electronically commutated motors (ECMs).
- Variable-Speed Air Conditioners & Heat Pumps
Instead of snapping on at full speed, these systems start slowly and gradually ramp up. The staged startup avoids large inrush currents, which helps stabilize your lights. An added bonus: variable-speed systems are more energy efficient and provide better comfort control. - ECM Motors
Found in modern HVAC systems, ECM motors are designed to use less energy and start more smoothly than traditional single-stage motors. This reduces both light flicker and overall power consumption.
While upgrading appliances can require an investment, the efficiency gains and improved comfort often offset the cost over time.
Electrical Panel and Circuit Upgrades
If you’re noticing significant dimming when appliances start, your home’s electrical system may need attention:
- Dedicated Circuits – Major appliances like air conditioners, steam showers, or compressors should each have their own dedicated circuit. Sharing a circuit with lighting can make dimming worse.
- Panel Capacity – Older homes may have undersized electrical panels that weren’t designed for today’s load demands. Upgrading to a modern 200-amp service can provide the headroom needed for new appliances.
- Voltage Drop Mitigation – An electrician can test for voltage drop at startup and recommend wiring or breaker upgrades to keep power stable.
Soft Starters and Surge Protection
In some cases, a soft starter device can be added to an existing compressor or motor. This allows the appliance to start more gradually, reducing the sudden demand for electricity.
Pairing this with whole-home surge protection not only helps with dimming but also protects sensitive electronics from fluctuations caused by high-load appliances.
When to Call a Professional
Occasional flicker when a large motor starts is normal, but frequent or severe dimming may be a sign of:
- Loose or undersized wiring
- Overloaded circuits
- Failing equipment
- Issues with the utility’s service line
If you’re unsure, it’s best to call a licensed electrician to investigate. An inspection can quickly reveal whether a simple upgrade will solve the issue or if there’s a more serious problem behind the dimming.
The Bottom Line
Lights that dim when appliances start are usually the result of high inrush current from single-stage motors. The good news is that modern variable-speed compressors, ECM motors, and electrical upgrades offer effective solutions. Along the way, you’ll gain the added benefits of improved efficiency, lower energy bills, and a more comfortable home.