Light verification under the WELL Building Standard, a certification mark of the International WELL Building Institute, uses physical measurement of illuminance in lux to provide evidence about conditions in the completed project. This page explains what the scheme does with that measured quantity, how the result fits into review, and why evidence gathered from an operating space is different from a design calculation. The practical method by which lux is measured belongs to a separate lighting-measurement resource and is not explained here.
Illuminance expresses the amount of light arriving at a surface and is reported in lux. Under the scheme, it is one of the quantities that can be established during on-site performance verification rather than inferred solely from drawings, product schedules or design software. The measurement produces evidence tied to a particular place, time and set of operating conditions.
Light is one of the five concepts included in on-site performance verification, together with Air, Water, Thermal Comfort and Sound. The site work is carried out by a WELL Performance Testing Agent working for an approved performance testing provider. A separate WELL Reviewer later assesses the measured evidence alongside the project documentation and decides whether the relevant feature has been achieved.
This separation prevents the measurement visit from being mistaken for the certification decision. The agent records the operating condition and the resulting illuminance evidence. The reviewer considers whether that evidence, in combination with the rest of the submission, satisfies the scheme's requirements.
A lux result is not treated as a general statement that a building is well lit. It is evidence for the particular feature and location to which it relates. The value must therefore remain connected to a clear space identifier, the relevant operating condition and the project boundary.
The reviewer considers whether the submitted result supports the feature being pursued. That review may also depend on plans, schedules or other project information that explains the use of the space and the intended lighting arrangement. The measured number is important, but its meaning within the submission depends on context.
For project teams, this means that an isolated spreadsheet of lux readings is not a complete evidential package. The result must be traceable to the measured area and consistent with the documentation that describes that area. If room names, layouts or uses have changed since design, the submission should avoid relying on obsolete labels that no longer correspond to the operating project.
A design calculation predicts illuminance from assumed information about the proposed space, lighting equipment, surfaces and operating arrangement. It is useful during design development, coordination and specification, but it represents an anticipated condition. The on-site measurement records what is present when the completed project is operating under the conditions used for verification.
The two forms of evidence answer different questions. A calculation asks what the design is expected to produce if its assumptions are realised. A measurement asks what illuminance was physically present at the selected location during the test event. Agreement between the two may support confidence in the design, but one does not automatically substitute for the other.
Differences can arise because the completed fit-out, furniture arrangement, controls, room use or lighting operation does not exactly match the design model. The purpose of performance verification is not to repeat the design calculation at the site. It is to obtain evidence from the finished environment that can be reviewed against the scheme.
Because illuminance responds to how a space is being operated, the project team should understand which lighting state is intended to represent normal use for the feature being pursued. Temporary construction lighting, incomplete control programming or manually overridden settings may produce a result that does not describe the completed operational arrangement.
The scheme does not impose a universal statement that every parameter must be tested during normal occupied hours. Timing and operating conditions are set according to the relevant parameter and project type, with defined exceptions elsewhere in performance verification. For light evidence, the important point is that the recorded condition must be appropriate to the applicable requirement and described accurately.
Occupancy itself may affect access, control settings and the ability to measure representative areas. The testing plan should therefore coordinate with facilities personnel without assuming that a busy period is always mandatory or that an empty room is always preferable. The applicable verification instruction governs the test condition.
A light-verification visit should occur when the relevant installation is complete enough to represent the intended operating project. Luminaires should be installed, controls should be functioning, and the measured spaces should correspond to the submitted layout. A room still being used as a construction store may not provide meaningful evidence for its intended occupied use.
Facilities and commissioning teams should also avoid last-minute changes that are not reflected in the project record. Temporary control overrides, disconnected fittings or unfinished scenes can make the measured condition difficult to reconcile with the documentation. Where a known operational state is required, it should be established consistently and recorded.
The site team should ensure that the agent can access the intended spaces and identify them without ambiguity. Repeated room names, changing tenancy layouts and incomplete wayfinding can cause readings to be associated with the wrong area unless the test record uses stable identifiers.
A measured result that differs from the design calculation does not, by itself, identify the cause. The difference may relate to the completed installation, the control state, the physical arrangement of the room or assumptions within the design information. The certification process uses the measured evidence to assess the pursued feature, not to conduct a general forensic investigation of lighting design.
Where a result does not support the feature, the project team may need to review the actual operating arrangement and the submitted documentation. Any subsequent change should be genuine, durable and consistent with the intended use of the building rather than a temporary test-only setting.
Conversely, a favourable reading should not be generalised beyond the tested evidence. It demonstrates the illuminance recorded at the selected location and condition. It does not establish every aspect of lighting quality, and it does not replace separate consideration of other lighting subjects.
The performance-testing record should connect each lux result to the project, space and test condition. Clear naming and consistent plans allow the WELL Reviewer to understand what was measured and how it relates to the feature. If the same room has different labels across drawings, commissioning records and test sheets, that inconsistency can create avoidable uncertainty.
The reviewer remains independent of the on-site agent. The agent's role is to carry out and document the performance verification, while the reviewer evaluates the evidence alongside the wider submission and decides whether the feature has been achieved. Neither the field reading nor a design consultant's calculation alone constitutes the scheme decision.
The number and location of test points across performance verification are governed separately and should not be inferred from general lighting practice. That subject is addressed on the page titled "Sampling points and test locations", while the detailed technique for obtaining lux readings is addressed by an independent lighting-measurement resource.
An independent resource. WELL is a certification mark of the International WELL Building Institute pbc. No affiliation, endorsement or accreditation.
A calculation and an on-site measurement serve different purposes. The calculation predicts performance from design assumptions, whereas the scheme uses illuminance measured in lux to provide evidence of the completed operating condition. Documentation remains relevant, but it does not turn a prediction into a physical result.
No. A WELL Performance Testing Agent working for an approved performance testing provider carries out the on-site work. A separate WELL Reviewer considers the results together with submitted documentation and decides whether the relevant feature is achieved.
No. Illuminance in lux is a specific measured quantity used for the applicable feature. It should not be treated as a complete judgement on every aspect of lighting design, visual experience or building operation.
There is no universal guidebook rule stating that all testing must occur during normal occupied hours. The applicable parameter and project type determine timing and operating conditions, and the test record should accurately describe the condition used.
The practical measurement method belongs to a separate specialist resource on workplace and building-lighting measurement. This page intentionally does not explain instruments, measurement technique, calibration, layout or related methodology.
This site is an independent information resource. It is not affiliated with, endorsed by, accredited by or authorised by the International WELL Building Institute pbc, which owns the WELL certification mark, and it is not a certification body, an assessor, a performance testing provider or a scheme partner. Nothing on this page can certify, assess or award anything under the scheme, and nothing here is a substitute for the scheme's own published documentation. Requirements are summarised factually rather than reproduced; where a numeric threshold is stated it is drawn from documentation the scheme's owner publishes openly, and the specific figure is cited rather than the table it sits in. Certification under the scheme is voluntary and is not required by any authority in the United Arab Emirates.