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Nonresidential Daylighting

Measure Description

This CASE Report will use a comprehensive approach to daylighting design and control strategies that maximize the use of natural light while minimizing glare and solar heat gain. Specifically, this CASE Report comprises several submeasures to promote more efficient use of daylight and to generate more energy savings, including Automatic Daylight Dimming to 10 Percent, Relative Solar Heat Gain Coefficient Equivalent for Louvers, Exterior Shading Thermal Breaks, Cleanup and Improvements to Daylighting Design Power Adjustment Factors, and Mandatory Secondary Daylit Zone Automatic Controls.

Automatic Daylight Dim to Off

This submeasure proposes to update the nonresidential automatic daylight dimming controls provision such that, for areas other than parking garages, when daylight illuminance is greater than 150 percent of the design illuminance received from the general lighting system at full power, the general lighting power in the daylit zone is turned off. This submeasure leverages the proliferation of solid-state lighting and its dimming capability in the nonresidential sector and takes full advantage of the 0-100 percent dimming range that is already required for LED luminaires and sources in Title 24, Part 6. The proposed dimming to OFF further aims to result in higher energy savings by promoting the 0-10V “dim-to-dark” LED drivers that cuts power to the LED light engines when dimming control voltage is close to 0V. The same dim-to-off result can also be achieved by other implementations, such as a 0-100 percent dimming driver with a power relay.

Relative Solar Heat Gain Coefficient (RSHGC) Equivalent for Louvers

This submeasure would improve the measurement of the Relative Solar Heat Gain Coefficient (RSHGC) to give projects the proper solar gain credit for louver devices. This would allow designers more flexibility in glazing selection.

Exterior Shading Thermal Breaks

This submeasure requires thermal breaks that mitigate heat transfer where exterior shading devices connect to interior spaces. The measure would likely only apply to certain climate zones.

Cleanup and Improvements to Daylighting Design Power Adjustment Factors

This submeasure reclassifies some features of daylighting power adjustment factors (PAF) from prescriptive to mandatory. Various improvements and simplifications will be proposed to definitions related to PAFs including distance factor, light shelves, and other minor changes. Additionally, this submeasure also proposes to add Northern orientations to the existing clerestory PAFs. Clerestories on the North side of the building are desirable because they eliminate direct beam sunlight glare.

Mandatory Secondary Daylit Zone Automatic Controls

This proposed submeasure would move the prescriptive requirements for automatic daylighting controls in secondary sidelit daylit zones (SDZs) to the mandatory section of the Title 24, part 6 energy code with all of the other lighting controls requirements. Currently, the requirement for automatic daylighting controls in SDZs is prescriptive, which means that users who choose the performance approach can trade-off other high efficiency features in the building against SDZ controls. This results in confusion and uncertainty during inspection about whether the controls in SDZs were traded-off, or if they were required and installed. As a prescriptive requirement, it is less likely that there is reliable enforcement of the controls requirements for the vast majority of buildings which have not chosen to trade-off the SDZ controls for another efficiency feature. By converting the SDZ controls requirements into mandatory requirements, this proposal will simplify the daylighting code and the compliance enforcement process, align Title 24’s daylighting code with that of ASHRAE 90.1, and reduce uncertainty about requirement for daylighting controls in SDZs resulting in greater likelihood that lighting in SDZs are controlled with photocontrols.

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This measure description will be updated as research is developed to support the 2022 code cycle. For questions or suggestions, email Include the measure name in the subject line.



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The Statewide CASE Team values input from all stakeholders engaged in the Title 24, Part 6 code change process. We encourage the open exchange of code change comments and concerns.

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