Separate the task from the equipment
Begin by describing the activity: a pedestrian route, an entrance or an area used only occasionally. That description is more useful than starting with a preferred wattage. A brief should state where light is needed, when the space is used and what the surrounding conditions are.
Compare useful output and input power
The US Department of Energy describes luminaire efficacy as light output divided by electrical input, expressed in lumens per watt. This provides one comparison of efficiency, but the project still needs to consider where the light is directed. A higher total output does not by itself describe an appropriate layout.
Make the schedule part of the design
The same guidance identifies automatic controls as another opportunity to reduce energy use. For your project, record the periods of regular activity and any different weekend or seasonal patterns. Discuss whether switching, dimming or a different operating profile is suitable for the actual task.
Build a comparison you can review
Ask for the proposed configuration, operating assumptions and supporting product information. For an existing installation, document the current equipment and schedule before comparing alternatives. This creates a clear basis for a project-specific discussion instead of relying on a general saving percentage.
Bring these points to the conversation.
- Mark the exact areas to be illuminated.
- Record the existing lighting and hours of operation.
- Explain any periods of lower activity.
- Request a comparison based on agreed assumptions.
Source and further reading
US Department of Energy — Energy-efficient exterior lighting ↗
The source explains general lighting principles and US federal procurement guidance. Its procurement thresholds are not presented here as UK requirements.
Source checked: 25 October 2026. Our project questions and checklists are editorial guidance; they are not product performance claims.