Measure Overview
The proposed code change would introduce a new mandatory daylight responsive control requirement for greenhouses with supplemental electric lighting. The requirement would apply to greenhouse facilities with more than 40 kW of connected horticultural lighting load and would provide two compliance options:
- Option 1: Timeclock + PAR Sensor-Based Control
Combines a scheduling device with dimming control in response to instantaneous Photosynthetic Photon Flux Density (PPFD) levels.
- Option 2: Daily Light Integral (DLI) Control
Automatically adjusts supplemental lighting based on cumulative PPFD measured over the daily photoperiod to meet, but not exceed, a user-defined DLI target.
The proposed code change would apply to both new construction and alterations of greenhouse facilities. The requirement would not be climate-zone dependent, and no compliance software updates would be anticipated. However, an acceptance test protocol for use by field technicians at the time of installation is proposed to ensure the proper functionality of the required controls. For this proposal, field technicians are generally the controls installer or an equivalent role and are not required to be certified acceptance technicians.
The proposed code change would also clarify requirements for indoor grow facility lighting controls. Because of a lack of clarity, stakeholders may erroneously interpret the current code requirements for control strategies to imply that a simple time switch is sufficient and that astronomical time switches are appropriate for indoor growing. The code language clean-up proposed in this report would explicitly specify that automatic scheduling devices capable of dimming the horticulture lighting and turning it on and off are required for indoor grow facilities.
In addition, the proposed code change would move the indoor grow facility electrical power distribution systems requirement that is currently in the broader CEH section to instead be in the CEH Lighting Controls section and explicitly include greenhouse lighting under the same 40-kW threshold.
Table 1 summarizes the scope of the proposed code change. Note that this proposal has acceptance testing performed by a field technician. Because the field technician is typically a member if the installation team, this acceptance testing is not considered “third party verification.”
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Scope of Proposed Code Change
| Building Type(s) | Construction Type(s) | Type of Change | Updates to Compliance Software | Third Party Verification |
| Nonresidential | New construction, additions, alterations | Mandatory | No updates | Add new verification requirements |
Justification for Proposed Change
CEH is one of California’s fastest-growing and most energy-intensive energy end-uses, driven by the rapid expansion of greenhouses that use supplemental light for crops like cannabis, leafy greens, and vine vegetables. Without stronger controls, this sector risks locking in years of unnecessary energy use and higher operating costs for growers.
Based on published field studies, the proposed daylight responsive controls requirement would deliver measurable and persistent energy savings ranging from an estimated 9 percent1 to 26 percent2 while improving crop consistency and grower control. Additionally, a recent model-based study shows that some specific pairings of greenhouse locations and crops in California can save up to 81 percent of lighting energy use by deploying DLI controls as compared to basic scheduling or photoperiod timers where the lights turn on at full power for 12 hours3. By automatically adjusting lighting in response to daylight availability, the measure ensures that plants receive the optimal amount of light each day to grow effectively while avoiding the waste of over-lighting. This practice reduces electricity use and lowers cooling loads. This reduction is particularly impactful during the grid’s critical peak hours—typically mid-to-late afternoons—when widespread energy use, primarily from air conditioning, puts the entire electrical grid under its greatest stress.
The proposal provides growers with flexibility and choice. They may select between a timeclock + PAR sensor pathway or a more advanced DLI pathway. Both options reduce wasted energy, though the DLI option enables even greater savings and performance improvements. Importantly, the measure is designed to be practical by not imposing additional software burdens and ensuring compliance verification would remain straightforward with possible enhancements through an acceptance test protocol.
From a policy perspective, this proposal builds directly upon the 2022 and 2025 Title 24, Part 6 CEH measures, which first set minimum PPE requirements for horticultural lighting along with time-clock controls and dimming requirements. By layering in daylight responsive controls, Title 24 can take the next step in California’s multi-cycle strategy for CEH efficiency and decarbonization.
Under the current language, some stakeholders may interpret a simple time-switch—or even astronomical time-switch controls—as sufficient for indoor growing facilities. However, these approaches do not always adequately address the dimming requirements in the current code language, which ensures the controls can respond to the lighting needs of crops in indoor grow environments. The proposal would close an existing compliance gap by explicitly stating that automatic scheduling devices capable of dimming the horticulture lighting and turning it off are required, preventing misapplication of lower-performing strategies in energy-intensive facilities.
The language clean-up proposal would also simplify compliance verification for building officials by consolidating the electrical power distribution monitoring requirements into the CEH Lighting Controls section and extending them to greenhouse facilities under the same 40 kW threshold. This ensures consistent treatment of CEH lighting systems, reduces ambiguity for enforcement staff, and streamlines compliance forms for project teams. By clarifying compliance pathways, the proposal minimizes confusion in plan review and field inspection, addressing one of the most cited barriers to effectively enforcing CEH measures.
Relevant Documents
Round One Utility-Sponsored Stakeholder Meeting Materials
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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.