Dear LightingTaxDeduction.org,

What exactly are the minimum recommended calculated light levels as established in the Ninth Edition of the IES Lighting Handbook?

Answer: You are, of course, referring to a requirement to qualify using the Interim Lighting Rule that the new lighting provide minimum recommended light levels as established by the Handbook. The answer depends on the application and task. The Ninth Edition of the IES Lighting Handbook provides a list of applications/tasks in a blue-coded section in the middle of the book. For each application/task, a number of design quality factors are shown, color-shaded to show their relative importance for that application/task. For illuminance (light level), letters are assigned, A through I, in an order of very low light levels recommended (A) up to very high (I).

Examples:

Orientation and simple visual tasks

A - public spaces - 3 footcandles (fc)

Common visual tasks

E - performance of visual tasks of high contrast and small size, or visual tasks of low contrast and large size - 50 fc

Special visual tasks

G - performance of visual tasks near threshold - 300 - 1000 fc

So these values are then assigned to common application/tasks and whether the light level is horizontal workplane or vertical. Below are examples for office spaces, showing horizontal workplane recommended maintained light level values:

Offices

Open plan office, intensive VDT use - D (30 fc)
Open plan office, intermittent VDT use - E (50 fc)
Private office - E (50 fc)
Mail sorting - C (10 fc)

 

For more information, you should obtain a copy of the Ninth Edition of the IES Lighting Handbook or the Fourth Edition of the Ready Reference (RR-03) from IES. Local lighting designers, electrical contractors, electrical wholesale distributors, local area representatives of lighting equipment manufacturers, or the lighting specialist at the electrical utility company may have access to these publications.

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