[SML] Computing a lighting load

[Dougherty, Jim]

When looking at a lighting system (particularly in the context of a new or replacement installation), is there a formula used to calculate a systems lighting load?  For example, assume an installation has 200 2.4K dimmers. To size the service at 4000A to handle the load if the system were to be run entirely at full is ridiculous.  How is it, then, designed/specified?  Based on a percentage of that maximum?  Taking into account a typical or perhaps maximum instrument count from past shows, and applying a formula to that number based on the assumption that no plot's lights are all on at once?  Darts and a Square D catalog?

Ideally I'm looking for a reference based on manufacturer's requirements, NEC, industry standard, etc.  Rule of thumb is definitely welcome but not as helpful in this context.  I find it interesting that the load will presumably be diminishing over time as our industry gradually shifts to a greater reliance on LED and other lower-load fixtures.  Our own system will be a mix of conventional and LED for a long time to come.

Thanks.

- Jim Dougherty
ATD, Middlebury College Theatre Dept.
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