The Design Brief™ | Volume VIII | How to Calculate the Quantity of Light Needed in a Space

Often—when specifying lighting fixtures for a space or designing a lighting scheme for a new construction project—interior designers select and locate fixtures based on a best guess approach. This often results in success because one bulb can be swapped out for another with more or less intensity fairly easily, OR dimmers can be used to adjust the light intensity to what works best. This latter approach—relying on dimmers to tweak the lighting intensity—is particularly useful, as the residential building codes and energy codes now require dimmers in residential new construction and renovation projects. 

Pro Tip: The 2024 edition of the International Residential Code, Section 1104.2.1 requires that all permanently installed luminaires (light fixtures) in habitable rooms (which excludes closets and hallways) be controlled with a manual dimmer or automatic shutoff control (motion sensor). Not all jurisdictions may be enforcing this requirement, but wherever dimmers are used, there is great latitude to control light levels. Need a codes refresh? Check out our codes handbook here.

The rationale behind dimmer and sensor mandates is not to accommodate inaccurate lighting level calculations. It is rather to reduce energy consumption when lighting levels are too bright, or when lights are left on in rooms that are not occupied. 

Is There a Formula to Compute Appropriate Lighting Intensity?

Join The DTS Files to learn exactly how to calculate how much light a space needs.