Lighting was one of the first uses of electricity and it’s still a core part of any electrical load calculation today. Even though it seems simple, lighting loads can be surprisingly complex. The rules for completing proper lighting load calculations vary depending on whether the project is residential or commercial and there are different requirements for different types of lighting. In this post, we’ll break it all down to make it easy to calculate the lighting load for your next project.
Residential lighting load calculations (dwelling units)
For most homes, lighting load calculations are straightforward. The NEC allows you to use a general unit load factor of 3 VA per square foot, so you don’t have to count or quantify each light fixture. This includes track lighting: there’s no need to count this separately unless there is something really unusual about the lighting setup. Just take the square footage, multiply by 3, and you’re done with the base load.
Once you’ve calculated the initial lighting load, you can then apply a demand factor. In NEC 2023, you’ll find these in Table 220.45. For NEC 2020 and 2017, refer to Table 220.42.
Once you’ve calculated the initial lighting load, you can then apply a demand factor. In NEC 2023, you’ll find these in Table 220.45. For NEC 2020 and 2017, refer to Table 220.42.
Commercial lighting load calculations (non-dwelling)
Commercial projects require a bit more attention to detail to calculate the lighting load. First, you’ll need to figure out whether you’re calculating for general lighting based on occupancy type or for specific lighting devices. Each path has different rules.
General lighting
For general lighting, check Table 220.42 (NEC 2023) or Table 220.12 (NEC 2020 and 2017) to find the required volt-ampere per square foot based on occupancy type (like offices, restaurants, warehouses, etc.). There can be significant differences between code years, so make sure you’re using the NEC edition your jurisdiction requires. For example, the VA value for schools/universities and sports arenas changed from 3VA/sqft in 2020 to 1.5VA/sqft in 2023.
Once you’ve calculated the total lighting load, you can again apply the demand factors from Table 220.45 (NEC 2023) or Table 220.42 (NEC 2020 and 2017).
Once you’ve calculated the total lighting load, you can again apply the demand factors from Table 220.45 (NEC 2023) or Table 220.42 (NEC 2020 and 2017).
Specific lighting devices
For specific lighting types, you’ll need to reference other parts of Article 220. Some special scenarios are listed below.
- Show-window lighting: NEC 220.46 requires at least 200 VA per linear foot (or 660 VA per linear meter) measured along the base.
- Track lighting (outside of dwelling units or hotel rooms): NEC 220.46 requires 150 VA per 2 feet of track. If the track is powered through a current-limiting device, you can use the device rating instead.
- Other lighting loads: NEC 220.14 includes other lighting types like luminaires (where you use the maximum VA rating of the fixture), heavy-duty lampholders (where you count 600 VA minimum per outlet), and sign and outline lighting (where you use 1200 VA per required branch circuit per 600.5(A)).
These rules are consistent across NEC 2017, 2020, and 2023 editions, though it’s always worth confirming all calculations with your codebook to be sure.
Avoid overestimating lighting loads
We’ve seen electricians overestimate lighting loads when they don’t have demand factors or code tables handy. Sometimes it helps to play it safe, but this can lead to unnecessary costs and complexity. With the right tools and code knowledge, you can calculate with confidence and build smarter to save time and money for you and your clients.
At Kopperfield, every lighting load calc — residential or commercial — automatically applies NEC demand factors and lookups based on your inputs. Whether it’s track lighting or show windows, our load calculator has it covered. Tens of thousands of electricians have already run load calculations through our tool to get the correct lighting load out of the box.
At Kopperfield, every lighting load calc — residential or commercial — automatically applies NEC demand factors and lookups based on your inputs. Whether it’s track lighting or show windows, our load calculator has it covered. Tens of thousands of electricians have already run load calculations through our tool to get the correct lighting load out of the box.
Ready to simplify your lighting load calcs?
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