Xcel Energy – LBNL ‘Beyond Widgets’ Project Workstation Specific Lighting with Daylight Dimming Controls System Program Manual

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This program manual was developed through a U.S. Department of Energy project to develop streamlined utility program approaches to the deployment of integrated systems in commercial offices. Integrated systems present deep opportunities for energy savings, however by nature these systems have additional levels of complexity and effort required for their design and energy savings assessment, which create barriers for utility incentive programs to develop streamlined cost effective incentive programs to capture these savings. This project worked with Xcel Energy in Colorado and Minnesota to select an integrated system and develop a streamlined approach to its deployment for small and large commercial offices.

Xcel Energy worked with LBNL to select a workstation specific lighting system with daylight dimming controls, applied as a retrofit in commercial office spaces. Previous studies indicated a potential lighting annual energy savings of 28-63%, with an average of 47% for this system type, due to reduced fixture LPD and controls only, not including a full fixture replacement from a condition such as T8 to LED. Xcel also had a desire to incorporate this fixture replacement in their integrated system package, and as a result annual energy lighting savings are expected to be higher. FLEXLAB testing of the system for 500 lux minimum output conditions translated into a 94% annual energy savings for this system.

Market analysis was developed for large and medium commercial office buildings in Xcel’s Minnesota and Colorado markets showing a potential for 48-295 and 120-672 GWh of energy savings potential for Colorado and Minnesota respectively. Total Resource Costs (TRC) vary by location and technology package used (enterprise versus non-enterprise lighting controls system), and vary from 0.29 to 1.27 and 0.06 and 0.44 for a Retrofit case, and 0.20 to 1.63 and 0.07 to 0.57 for a Replace on Burnout strategy for Colorado and Minnesota respectively. These results indicate good potential for demonstrating a strong technical and economic case for deployment of this system type in Xcel’s Colorado territory, while deployment in the Minnesota market may be advisable as well as part of a portfolio of programs, or as an effort to help shift the market into integrated systems deployment in general. It should be noted that the cost of avoided energy in both markets is significantly low ($0.07/kWh for Minnesota, $0.08/kWh for Colorado), and these TRC values would not be representative of deployment potential in other markets with higher utility rates. In addition, installation costs used for these systems may decrease with time, further enhancing their return on investment.

This program manual documents candidate site criteria for selection to implement this system through a utility incentive program. The system was also configured and tested in LBNL’s FLEXLAB™ (flexlab.lbl.gov) under conditions representing a range of implementations of the system including different tuned light output levels at the occupant’s workstation (300 and 500 lux) and different light fixture types (LED pendant and troffer). The FLEXLAB testing demonstrated strong energy savings against the baseline case of a T-8 zonal lighting configuration typical for Xcel’s office market, with 94% annual lighting energy savings during daylight hours (7am – 7pm), and ~87% annual energy savings overall all hours. These results validated the energy savings potential illustrated by earlier work, and also provided empirical data to develop a streamlined customer savings assessment methodology. This methodology assesses the annual energy savings potential from reduced installed LPD. A study was conducted to assess whether variances in workplane illuminance values, and LPD would change significantly for a range of occupant densities not tested in the FLEXLAB tests. The tested case was the 2015 International Building Code maximum occupant density of 100 gross sf/person. Simulation studies of a 150 gross sf/person condition did not result in a significant difference in LPD, while the illuminance minimums were still met in the space.

The FLEXLAB™ test data also validated that minimum light levels were achieved in the workplane and egress areas. Visual comfort performance was evaluated for the workstation specific lighting system tested in FLEXLAB through the use of High Dynamic Range imaging to evaluate Discomfort Glare Performance. The workstations specific lighting systems demonstrated good visual comfort performance consistent with that experienced with other lighting system types, over the seasonal variations studied, including summer, fall and low sun angle conditions in winter. Some periods of higher levels of DGP were documented, also consistent with other lighting systems deployment that did not employ shading to block direct sunlight into the work space. To ensure satisfactory DGP is experienced throughout the course of all times of day and seasons, the use of an adjustable shading system is required to block out direct solar radiation. A venetian blind system would be recommended in order to allow for direct sun angle to be controlled while still permitting daylighting in to benefit the space.

Implementation guidance is presented in this program manual to assist utility program managers in their design of incentive programs and educate customers on key aspects of the system to focus on in commissioning and operations to ensure that lighting savings are realized. These include aspects such as a requirement for a commissioned lighting system that tunes light output levels to desired lux levels at the workplane, and verification that daylight dimming controls features are enabled and perform as desired.

Overall, workstation specific lighting systems with daylight dimming controls present a very strong potential for cost effective lighting energy savings, as demonstrated by the FLEXLAB test results and previous case studies. Further energy savings may be realized from the use of fixture-specific occupancy sensors as well, although this approach was not considered in this study.

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