During schematic design, work with owner/client to understand electric lighting needs and develop a strategy to meet needs while conserving energy and maintaining a high environmental quality. For each regularly occupied interior space, establish and document the light levels recommended for primary (and secondary) use type using B3 Lighting Space Tracking Worksheet.
Calculate target levels to maintain contrast ratios between spaces and surfaces as described above. For contrast ratios between work surfaces and wall surfaces (excluding fenestration), use the following calculation for illuminance ratio:
1:(Average work surface illuminance / Average wall surface illuminance)
For example, if the target average work surface illuminance is 40fc, the target wall surface illuminance should be at least 13fc to maintain the desired 1:3 ratio.
For contrast ratios between work surfaces and ceiling surfaces (excluding fenestration) use the following calculation for illuminance ratio:
1:(Average work surface illuminance / Average Ceiling illuminance)
For example, if the target average work surface illuminance is 40fc, the target ceiling surface illuminance should be at least 4fc to not exceed the 1:10 ratio.
Establish criteria for and document the interior surface reflections, based on manufacturer cutsheets, reflectance chart, or by using the calculation methodology described in IES Lighting Handbook. Specify the light fixture direction and lensing if following Recommended Guideline I.5F, Light Direction and Glare.
During design development and in construction documents, simulate electric lighting to confirm desired light levels at appropriate height, including wall or ceiling illuminance to confirm contrast ratios, and document results. Simulation of light levels should be completed for all regularly occupied spaces, and simulations should accurately reflect interior surface reflectance and include permanently installed furniture that may affect light levels. If needed, adjust lighting strategy to meet goals established in previous step.
During schematic design and design development, simulate the daylighting utilization in main spaces. Ensure that daylight models accurately reflect room size, height, window placement, glazing properties, interior surface reflectance, and permanently installed furnishings. If none of the following targets can be met, adjust the design to ensure compliance.
There are several daylighting metrics that may be used to comply with the B3 Guidelines and which are available as outputs daylight modeling software:
- Spatial daylight autonomy (sDA) is an annual measure that determines the percentage of the floor area that receives the minimum light level required for at least 50% of the occupied hours. The threshold for sufficient daylight will be determined based on the recommended IES light levels for the program of the space.
- Point-in-time daylight calculations to confirm light levels within 20% of IES recommended levels for 75% of regularly occupied floor area should be done at 9 a.m. and 3 p.m. on the equinox.
- Daylight factor is the ratio of the illumination available inside a structure to the illumination outside, based calculated or measured from an overcast sky condition.
Compliance with this guideline may be documented using simplified daylight modeling software (e.g., Sefaira) which does not permit reflectance of materials if the following minimum area-weighted surface reflectance is achieved:
- 80% ceilings
- 50% walls
- 20% floors
When selecting and/or specifying light fixtures, ensure that the criteria of CRI and RoHS compliance are met or mandated in specifications. This information can typically be found on manufacturers cutsheets.
If following Recommended Guideline I.5E, evaluate lighting plans and identify spaces with direct-only overhead lighting. Calculate the total connected lighting load in area served by the direct-only overhead lighting, and if direct-only overhead lighting exceeds 25% of the total connected load, select different fixtures to meet the criteria.
If following Recommended Guideline I.5F, select or specify interior surfaces with reflectance to meet or exceed the values listed. This information can be found on manufacturer specifications, typically listed as a fraction of percentage light reflectance or light reflectance value. If the manufacturer’s data does not include reflectance, use the methodology described in the IES Lighting Handbook to calculate the surface reflectance with a product sample or installed product.