Task 21
Task 21
SHC Task 21

Daylight in Buildings

Project (Task) Conclusions

IEA SHC Task 21 has documented the potential energy savings possible with advanced daylighting strategies that manage the flow of light and heat. For the first time innovative daylighting systems have been evaluated on a comparative basis. The assessments performed in real and scale-model buildings and in test rooms worldwide, show that the majority of the systems tested can produce potential energy savings when applied in the appropriate climates and on the appropriate orientations of a building.

The Task has also laid the foundation for ongoing research and assessment by establishing testing facilities to monitor new systems, measure their physical characteristics for software input, and to evaluate systems when they are installed in actual buildings. As a result of this work, manufacturers of daylighting products can now test new devices using proven methods, develop these products further, and assess their performance using post-occupancy evaluation procedures.

A daylighting system should be selected according to climatic characteristics, e.g., the predominant sky type and the latitude at a building site. Actual energy savings depend on the daylighting system being designed as part of an integrated strategy that includes daylight-responsive controls. Careful integration of the daylighting system with the rest of a building’s design should begin early in the design process to produce a high-quality work environment and provide building owners with a highly valued space.

The state-of-the art of designing daylit buildings in practice varies widely in different countries. The European tradition, as embodied in typical design practice and building codes, places more emphasis on floor plans that are conducive to daylight utilisation in climates and latitudes where this resource is limited in availability. North America and Australian climates, with an abundance of daylight and sunlight in most regions, have also to contend with the problem of cooling loads and therefore have not in the past relied as much on utilising daylight. Now with a renewed interest in reducing energy use and the improvement of working conditions, the use of innovative daylighting strategies is becoming a positive element in building design.

The advanced daylighting systems studied in the Task are intended to address the following challenges posed by traditional daylighting strategies:

  • In predominantly overcast climates or in built-up urban areas, there is insufficient daylight flux to provide adequate interior daylighting.
  • In some climates and orientations, poor control of glare from direct sunlight limits daylight applications.
  • In hot and sunny climates, daylighting designs must manage sunlight to control cooling loads.
  • There is widespread interest in extending the floor area that can be effectively daylighted at a distance from windows and skylights.
  • Given the ever-changing nature of tasks in buildings and the dynamic nature of daylight, design solutions that provide some degree of operational control are desirable.
  • Even when the technology exists, it is often difficult to characterise performance in a manner that allows designers to reliably predict long-term performance.


Although it was feasible to extend limited test room data to annual performance data this was not always possible. As the testing was carried out in different facilities in different countries, it was difficult to make comparisons between the data.

In order to best utilise the results of the Task, the designer must carefully evaluate the performance data presented in relation to the performance needs of the specific project that is being considered. The “best” system for a particular project may turn out not to be useful for another project because of differing performance requirements.


Although the work documented demonstrates that improved optical systems can provide better daylighting performance, greater occupant acceptance, and increased energy savings potential as compared with conventional systems, the rapid and continuing advances in materials science and production technologies promise additional performance improvements as well as reduced costs and maintenance. Beyond advances in optical components, however, critical elements of daylighting design still need to be addressed. These include the successful integration of advanced daylighting systems with daylight-responsive lighting controls, the consideration of occupant response to advanced daylighting strategies. Two key focuses for future research are the development of a comprehensive understanding of occupant needs and preferences in daylighted spaces, and the creation of models that describe the relationships among daylighting design parameters, occupant satisfaction, and control systems.

Past electric lighting energy savings mainly resulted from advances in the efficiency of lamps; future savings will be the result of using advanced daylighting systems and controls. Window and lighting system designs need to be integrated to maximise daylight while minimising cooling loads so that daylighting strategies can produce consistent energy savings. Cost-effective integrated design solutions are needed that have thermal impacts equal to or lower than those found in the best available conventional building designs. There is also the need for standards and guidelines to apply to these systems.

The work of SHC Task 21 is offered as a first step toward harmonising the needs of people with the advantages that technology can provide, and integrating the hardware and software elements of daylighting systems throughout the major phases of building life cycles.