AT A GLANCE
- Find AC input amps at your supply voltage and chosen power setting; leave the LED-side output current out of the calculation.
- Calculate the running-load count. For continuous lighting on a standard circuit, 15A allows 12A and 20A allows 16A. At an assumed 0.50A per light, that is 24 or 32 lights.
- Account for shared equipment and confirm how many lights can start and be switched together. Motors need a separate assessment.
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Keep each linked run within its rating. Insufficient running capacity calls for fewer lights or added circuit capacity. Separate switching groups may address startup or control limits.
On this page
The number of LED lights you can run on a 15- or 20-amp circuit depends on each fixture's AC input current and what else uses that circuit.
For a lighting-only circuit used through a workshift, the example below gives 24 lights on 15A or 32 lights on 20A. Each light is assumed to draw 0.50A at 120V. Shared equipment and startup can lower those counts; linked runs also have separate connection limits.
| Circuit rating | Current available for continuous lighting | Example count at 0.50A per light |
|---|---|---|
| 15A | 12A | 24 lights |
| 20A | 16A | 32 lights |
Find the AC input amps for your light
Use the input-current value for your supply voltage and selected power setting. The input is the side connected to the building's power. A driver can also show a DC output current for the LEDs; that is a different value.
On an actual label, look for INPUT, the matching voltage and a value in A. If several voltages have different currents, use the entry for your supply. For an adjustable light, give the installer both the planned setting and the highest setting the fixture can use. A later increase in power can change the circuit load.
If the label gives only watts, obtain the model's AC input-current data. A specification marked "typical" also needs confirmation before you treat it as a maximum. Use an accessible label or the specification sheet; your installer can identify anything that requires opening equipment.
Calculate the lighting-only count
Lighting that stays at its expected maximum load for at least three hours is a continuous load. On a standard circuit, the continuous-load calculation uses 80% of the breaker rating: 15A × 0.80 = 12A, or 20A × 0.80 = 16A.
Divide that available current by the input current of one light:
20A circuit: 16A ÷ 0.50A = 32 lights
Round down if the division leaves a fraction. These are running-load counts. Before ordering, apply the limits below to the same group of lights.
Why the usable number may be lower
Other equipment needs part of the circuit
The lighting allowance belongs to the whole circuit, including loads at other outlets. Suppose the same 15A circuit already supplies another 3A of continuous, non-motor load. That leaves 12A − 3A = 9A for the example lights: 9A ÷ 0.50A = 18 lights.
A compressor or saw needs a different assessment. Motors have their own sizing rules and a starting demand. Give the electrician the equipment models and which items can run together; subtracting their average running current will not establish the remaining lighting capacity.
Starting the lights can trip a circuit that runs them comfortably
LED drivers can draw a brief surge when power is first applied. When many start together, their combined surge may trip the breaker even though their steady current fits the calculation.
Ask the lighting supplier whether it has a tested maximum fixture count for your driver and breaker combination. Give it the breaker and wall-control models identified by your installer. If no compatibility table is available, ask the supplier for the driver's inrush-current peak and pulse duration; your installer uses those figures to assess startup.
A wall switch, dimmer or sensor also needs a suitable LED load rating. Its general amp rating alone does not establish how many LED drivers it can switch.
A linked run has a limit of its own
A circuit may have capacity left while a linked run has already reached its rated limit. The cord and connectors carry the load of the connected units, so keep within the product's maximum connected count and load.
For construction string lights, the rated unit may be an entire string with several light heads. Use the whole string's input and linking instructions. The 24/32 example does not authorize connecting that many strings.
Use the count to make a specific purchase decision
First keep the total load on the circuit within its capacity. Confirm how many fixtures can start and be switched together, then divide linked products into runs that each meet their own rated count and load. A per-run limit controls the grouping; it does not automatically cap the circuit’s total fixture count.
If the switching limit is the remaining unknown, ask the supplier one concrete question:
At my supply voltage, can this exact light and driver start together in my planned quantity on this breaker and wall control?
Include the product link, quantity and the breaker/control model details from your installer. If the answer only repeats the fixture's watts, the startup question remains unanswered.
When comparing GGJIA workshop lighting, keep the chosen power setting with the quantity. Then consider whether that layout puts enough light on the work. Our workplace lighting guide explains where light levels need to be assessed. A circuit-capacity calculation cannot tell you whether the bench or aisle is adequately lit.
Sources
- Schneider Electric — 80% and 100% rated circuit breakers
- Schneider Electric — Load Planning
- MEAN WELL — HLG-60H-C input, output and inrush-current fields
- Eaton — LED drivers and circuit-breaker selection
- Eaton — Residential products brochure, circuit protection
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