Quick answer: A 100 watt LED light uses about 0.83 amps at 120V, 0.42 amps at 240V, 8.33 amps at 12V, and 4.17 amps at 24V. Use amps = watts / volts, then add margin for drivers, inverters, low battery voltage, and long wire runs.
100W LED Amp Draw Table
| Voltage | Calculation | Estimated current | Typical use |
|---|---|---|---|
| 120V AC | 100W / 120V | 0.83A | Garage outlet or hardwired fixture |
| 240V AC | 100W / 240V | 0.42A | Commercial or higher-voltage circuit |
| 12V DC | 100W / 12V | 8.33A | Vehicle, RV, battery, light bar |
| 13.8V DC | 100W / 13.8V | 7.25A | Vehicle while alternator is charging |
| 24V DC | 100W / 24V | 4.17A | Truck, solar, off-grid systems |
Why The Same Light Draws Different Amps
| Setup | What changes | Planning note |
|---|---|---|
| 120V plug-in light | Higher voltage means lower current | A watt meter can confirm real draw |
| 12V battery light | Lower voltage means higher current | Fuse and wire size matter more |
| Inverter setup | Battery supplies the AC load plus inverter losses | Battery current is higher than simple AC current |
| Long DC cable | Voltage drop wastes power | Use wire sized for current and round-trip length |
| Advertised LED wattage | May not equal input watts | Prefer label input watts or measured draw |
Fuse, Wire, And Circuit Notes
| Use case | Main concern | Safer direction |
|---|---|---|
| One 100W 12V light | About 8.33A before losses | Use a fused circuit close to the battery |
| Two 100W 12V lights | About 16.7A before losses | Check relay, switch, fuse, and wire rating |
| 120V garage fixture | Small amp load but still part of the circuit | Count other garage loads too |
| Battery runtime | 100W is a meaningful load | Use usable amp-hours, not just battery label size |
Related GarageSanctum Guides
Source Notes
- KC HiLiTES amp-draw support uses watts divided by volts to estimate lighting current.
- U.S. Department of Energy LED lighting guidance gives LED efficiency context.
