WELL v2 Light Concept: Preconditions, EML Thresholds, and Optimization Points (2024)

150 EML. That is the standard threshold for the first L03 point in WELL v2’s Light concept, measured on the vertical plane at eye level, beginning no later than noon. L03 is an optimization, so missing it costs points; it blocks certification only if the project relies on L01 Option 4. Get the measurement plane wrong and luminaires pass photometric testing but earn no L03 points. This article covers L01 through L06: the two preconditions, the EML thresholds, glare limits, and daylight optimization points.

What are the key numbers in WELL v2 Light?

WELL v2’s Light concept is a set of circadian, visual, and daylighting thresholds spanning 2 preconditions and up to 7 optimization features, L01 through L09. The framework uses two photometric metrics: lux for visual acuity compliance under L02, and Equivalent Melanopic Lux (EML) for circadian health compliance under L03. L01 and L02 carry no point value; failing either blocks WELL certification regardless of optimization scores. Point totals for L03 to L06 differ between standard WELL v2 and WELL Core, as the table shows.

What is the WELL Light concept?

WELL’s Light concept is a framework of circadian health, visual acuity, and daylighting requirements applied in any WELL v2 certified project. Two features are preconditions: L01 (Light Exposure) and L02 (Visual Lighting Design). Both must be satisfied before any optimization points count toward certification. Standard WELL v2 and WELL Core projects share the same preconditions but assign different maximum point totals to L03, L04, L05, and L06. The distinction between lux and EML defines the concept’s rationale. Standard photometric measures count all visible light equally. EML weights spectral output by the response of intrinsically photosensitive retinal ganglion cells (ipRGCs), the cells governing the circadian clock. Both EML and M-EDI(D65) are melanopic metrics calibrated differently from photopic lux. Spectral content changes EML relative to lux. A luminaire that meets the 320 lux horizontal task illuminance in L02 can still fall below the 150 EML vertical-plane threshold in L03.

What does L01 require for light exposure?

L01 Light Exposure is a precondition requiring spaces other than dwelling units to satisfy one of four compliance paths (dwelling units have three). Option 1 (Daylight Simulation) requires spatial Daylight Autonomy of at least 30% (sDA₂₀₀,₄₀%) across regularly occupied floor area, per IES LM-83-12. Common spaces with unassigned seating for 15% or more of regular occupants face a stricter threshold: sDA₃₀₀,₅₀% > 75% of floor area. Option 2 uses glazing proximity: 30% of regularly occupied area must fall within 6 m (20 ft) of envelope glazing; common spaces require 70% of seating within 5 m (16 ft). Option 3 requires glazing area of at least 7% of floor area per floor, or a floor plate no wider than 20 m (65 ft) with no opaque obstructions above 1 m (3.2 ft) within 6 m (20 ft) of glazing. Option 4 allows a project to comply through L03 Circadian Lighting Design. CEN 17037:2018 may substitute for IES LM-83-12 in Option 1: 200 lux (19 fc) for more than 30% of unit area throughout 50% of daylit hours.

What illuminance does L02 require for visual acuity?

L02 Visual Lighting Design is the second precondition, focused on horizontal task illuminance for visual acuity rather than circadian health. Option 2 (Predetermined Light Levels) sets fixed minimums: offices and classrooms require a minimum of 320 lux (30 foot-candles) at the task surface; lobbies, atriums, corridors, and outdoor pathways require 110 lux (10 fc) at floor level; dining areas, lounges, and restrooms require 110 lux (10 fc) at the task surface. Option 2 applies only when more than 50% of occupants are under 65 years old and at least 90% of floor area consists of listed space types. Option 1 (Full Design) requires compliance with illuminance thresholds from a recognized reference standard: IES Lighting Handbook 10th Edition, EN 12464-1:2011, ISO 8995-1:2002(E), GB50034-2013, or CIBSE SLL Code for Lighting. Option 1 requires accounting for task type and occupant age group.

How does circadian lighting design work in L03?

The vertical measurement plane separates L03 from standard photometric practice. Most photometric tools calculate illuminance on a horizontal work-plane. L03 Circadian Lighting Design measures on the vertical plane at eye level, at 45 cm (18 in) above the work-plane at workstations in regularly occupied spaces. L03 is an optimization feature worth up to 3 points in standard WELL v2 and up to 4 points in WELL Core. The standard threshold requires at least 150 EML [136 M-EDI(D65)] for at least 4 hours per day, beginning no later than noon. The 3-point threshold is 240 EML [218 M-EDI(D65)]. Projects may also qualify at lower EML thresholds when L05 Part 1 or L06 Part 1 is also satisfied: 120 EML [109 M-EDI(D65)] for 1 point, 180 EML [163 M-EDI(D65)] for 3 points. In dwelling units, the light levels must be dimmable, automated lighting must dim after 8:00 pm, and the measurement location shifts to living rooms and kitchens at 140 cm (55 in) above the floor in the center of the room (or 45 cm above the work-plane where workstations are present).

What glare limits apply under WELL v2 L04?

L04 Electric Light Glare Control is an optimization feature worth 2 points in standard WELL v2 and 1 point in WELL Core. L04 applies at the luminaire level. Every fixture in non-industrial regularly occupied spaces must satisfy one of three criteria: 100% of light emitted above the horizontal plane; a Unified Glare Rating (UGR) of 16 or below; or luminance of 6,000 cd/m² or less at any angle between 45 and 90 degrees from nadir. Space-wide compliance requires UGR of 16 or below across all regularly occupied spaces. Industrial spaces follow a higher tolerance: UGR of 19 or below, either per luminaire or space-wide. Wall wash, concealed, and decorative fixtures may be excluded from L04 glare calculations.

How do daylight design strategies earn points in L05 and L06?

L05 Daylight Design Strategies is an optimization feature offering up to 4 points in standard WELL v2 and 6 points in WELL Core. Part 1 sets glazing-proximity thresholds for workstations. The 1-point path requires 70% of workstations within 7.5 m (25 ft) of transparent envelope glazing with Visible Light Transmittance (VLT) above 40%, or glazing covering at least 15% of regularly occupied floor area with VLT above 40%. The 2-point path requires 70% of workstations within 5 m (16 ft) of glazing, or glazing coverage of at least 25% of regularly occupied floor area. Dwelling units use vertical envelope glazing as the reference area: 15% of unit area for 1 point, 25% for 2 points. Part 2 awards solar shading points: 1 point for manual shading controllable by occupants at all times; 2 points for shading automated to prevent glare. L06 Daylight Simulation awards 1 point when climate-based modeling shows sDA₃₀₀,₅₀% exceeding 55% of regularly occupied floor area, and 2 points above 75%, per IES LM-83-12 (CEN 17037 Annex A is the alternative method).

The part teams most often get wrong

Four documentation errors recur on WELL Light projects. First: measuring EML on the horizontal work-plane. L03 requires measurement on the vertical plane at eye level, 45 cm (18 in) above the work-plane. A photometric model calculated on a horizontal grid will not demonstrate L03 compliance. Second: applying the L01 Option 2 proximity threshold to total floor area. Regularly occupied area is the denominator; core circulation, storage, and service spaces do not count. Third: specifying warm-white lamps for a project targeting L03. Spectral content changes EML relative to lux. A source meeting 320 lux task illuminance may still fall below 150 EML at the vertical plane. Fourth: including wall wash, concealed, or decorative fixtures in L04 luminaire-level checks when they can be excluded. WELL v2 lets all three fixture types be excluded from the Option 1 requirements.