⚡ Dimmer Load Planner
Dimmer Load Calculator
Calculate how many LED fixtures your dimmer can safely support. Checks total load, derating, minimum load requirements, and dimmer-LED compatibility for residential and commercial circuits.
Dimmer type
Dimmer specification
Found on the dimmer faceplate or spec sheet
Many LED dimmers have no minimum. TRIAC types may require 25–60W min.
Lighting load
Wattage printed on bulb or driver label
Load analysis
Total load (W)
Derated capacity (W)
% of derated load
Max fixtures
Dimmer type guide
Choosing the right dimmer type for your load is as important as the wattage rating. Mismatched types cause flickering, buzzing, and premature failure.
←
Leading edge / TRIAC (LE)
Incandescent · Halogen · MLV
Traditional dimmer type. Works by cutting the front of each AC half-cycle. Causes flickering and buzzing with LED loads. Many have a minimum load (25–60W) that LEDs can’t meet. Avoid for LED use unless dimmer is specifically LED-rated.
→
Trailing edge (TE / ELV)
LED · CFL · ELV transformers
Cuts the trailing edge of each AC half-cycle. Much smoother for LED and capacitive loads. No minimum load requirement. Generates less heat, less flicker, and is significantly quieter than leading edge. The recommended choice for most LED dimming circuits.
🔌
Universal LED dimmer
LED · Most load types
Auto-detects load type and switches between leading and trailing edge modes. Best for mixed installations or when load type is uncertain. Usually slightly less efficient than a dedicated TE dimmer but far more flexible.
📊
0–10V / DALI
Commercial · Drivers · Panels
Separate control wire (0–10V analogue or digital DALI signal). No minimum load issue. Very smooth, linear dimming. Standard for commercial LED drivers, panels, and high-bay fixtures. Requires compatible LED driver. Not suitable for residential lamp replacement.
Understanding dimmer derating
The wattage printed on a dimmer is not the maximum safe LED load. Derating is required to prevent overheating and ensure long-term reliability.
🌡️
Why derate?
LED loads produce reactive current (capacitive) that causes more heat per watt in the dimmer than incandescent loads did. Running a 400W dimmer at 400W of LED load overheats the internal TRIAC or MOSFET, reducing life. Most manufacturers specify 75–85% derating for LED loads.
⚡
Typical derating factors
Trailing edge: 80%. Leading edge (with LED): 75%. Universal LED: 85%. 0–10V: typically 100% (load is on the driver, not the dimmer). DALI: 100%. Always verify with the specific manufacturer’s LED load derating table, as values vary by model.
🔦
Minimum load problem
Leading edge (TRIAC) dimmers require a minimum load to trigger the SCR correctly. A 400W dimmer with a 25W minimum and 4 × 5W LEDs (20W total) won’t dim at all — it will just flash. Solution: use a trailing edge dimmer or a ghost load resistor (less efficient).
🕒
Derating for ganged dimmers
When multiple dimmers share a gang box, heat dissipation is restricted. Manufacturers typically require additional derating (10–20% per ganged unit). A 600W dimmer in a 3-gang box may be derated to 360W. Always check the ganging derating table.
Common dimmer load mistakes
These are the most common causes of dimmer failure, flickering, and buzzing in LED installations
🔴
Running at 100% of rated wattage with LEDs — The wattage on the dimmer label assumes resistive (incandescent) loads. LEDs are capacitive and generate more heat per watt in the dimmer. Always derate to 75–85% of the rated maximum when installing LED loads.
⚡
Using a TRIAC dimmer with LEDs below the minimum load — LEDs are so efficient that 4–6 of them may not meet the dimmer’s minimum wattage threshold. Result: no dimming, just flashing. Switch to a trailing edge or universal LED dimmer with no minimum load requirement.
💡
Mixing dimmable and non-dimmable LEDs on the same circuit — Non-dimmable LEDs on a dimmed circuit will fail early or cause the dimmable LEDs on the circuit to behave erratically. All LED loads on a dimmed circuit must be dimmable.
🔇
Forgetting neutral wire for smart dimmers — Most smart dimmers (Lutron Caseta, Leviton Decora Smart, etc.) require a neutral wire. Many older UK/US installations only have a live and switched live at the switch position. Without neutral, the smart dimmer won’t work correctly or at all.
🏠
Not checking the dimmer’s LED compatibility list — Dimmer manufacturers publish tested LED brand/model compatibility lists. Even a “universal LED dimmer” will flicker with certain drivers. Verify your specific LED fixture or driver is on the compatibility list before installing.
🏗️
Ignoring ganging derating — Installing multiple dimmers in a shared backbox reduces airflow. A 600W dimmer rated solo may be derated to 360W when ganged with two others in the same box. Always consult the ganging derating table for your specific dimmer model.