A museum lighting plan is not complete when the track lights are installed. It is complete when the team has measured the light reaching each object, recorded the hours of exposure and agreed what to do when the exhibition changes. This guide gives curators, conservators, lighting designers and contractors a practical commissioning workflow for LED-lit exhibitions. It focuses on measurement and records rather than choosing a particular track-light model.

Why a finished installation still needs a measurement plan

A catalogue beam angle, wattage or lumen figure cannot tell a conservator how much light reaches a particular watercolor. The result depends on the distance and aim of the fixture, dimmer setting, neighbouring lights, glazing and daylight. A change to any one of these can change the exposure at the object while the equipment remains the same. The commissioning record therefore needs to describe the installed condition, not only the ordered products.

The Canadian Conservation Institute (CCI) defines illuminance as the amount of light falling on a surface, measured in lux. It explains that cumulative light exposure is illuminance multiplied by time, commonly expressed in lux-hours or millions of lux-hours (Mlx h). CCI also stresses that visible light itself can damage sensitive colourants; low ultraviolet output does not make an exhibition risk-free. The museum’s conservator or lender must set the acceptable display conditions for each object. A supplier should provide reliable dimming and photometric information so those conditions can be met and checked.

Step 1: Build an object and zone register

Before aiming the lighting, make a simple register of objects and locations. Give each object a stable identifier, note its material and display position, and record who sets its light and UV limits. Include lender requirements, planned opening dates and display hours. Avoid treating one room as one exposure category: a paper drawing in a case, a ceramic vessel and a wall label may need different lighting decisions even when they share the same space.

Map each object to a lighting zone or group of track heads. Note any daylight path from windows, doors or skylights. Identify scenes used for public viewing, installation, cleaning, events and security. If staff can change scenes, record who has permission and how the approved scene is restored. This prevents a temporary bright work light from becoming the ordinary exhibition setting.

Use the register to state the measurement point, not just the target. A framed work may need readings at several locations across its surface; a three-dimensional object may need readings on its most exposed faces. Inside a case, measure where the artifact actually sits with the final glazing, case light and nearby room lights in place. Do not substitute a floor-level reading for the light incident on a vertical work.

Step 2: Choose instruments and a repeatable method

Use a suitable, maintained lux meter for visible light and a museum-appropriate UV meter when UV assessment is required. Record the meter model, calibration or service date, unit, operator and time of measurement. CCI notes that some museum instruments combine lux and UV functions. A phone app may be useful for a rough orientation, but it should not replace the agreed instrument for an acceptance test where lender or conservation limits apply.

Place the sensor in the plane of the object, oriented toward the incident light as the object surface is. If a fragile work cannot be approached, use a safe stand-in or approved nearby position and record the offset and method. Never put the sensor on an object without the conservator’s approval. Keep the operator’s body, clipboard and meter cable from casting a shadow on the sensor. Repeat a reading if the value changes while someone moves in front of the beam.

Record the scene name, dimmer level, track-head positions and daylight condition with the reading. A value without those details is difficult to reproduce. If daylight varies, take readings at representative times or use a logger as appropriate; one morning snapshot cannot describe an afternoon sun patch. Keep electric-light and daylight observations separate where practical so the team knows which system requires correction.

Step 3: Measure the actual object plane

Set the room to the approved public-viewing scene. Allow the system to settle, then measure the brightest relevant point and one or more representative points across each object. Record all points rather than averaging away a hotspot. For a painting, a grid or selected corners and centre can reveal unevenness. For a display case, include the artifact position closest to the source. For a sculpture, note which face and orientation each reading represents.

Compare readings with the object-specific requirement supplied by the conservator. If a hotspot exceeds the target, adjust aim, shielding, beam distribution or dimming and measure again. A visible reflection in glazing or direct view of a source can also warrant correction even if the lux reading passes. Check typical visitor positions, including seated viewpoints. Conservation and viewing quality need to be reviewed together.

CCI’s guidance for new heritage collection facilities says exhibition areas should be capable of levels as low as 50 lux where light-sensitive objects may be displayed. That is a design capability, not a universal prescription. Do not copy a 50-lux setting onto every object or assume a higher reading is acceptable for every painting. The responsible conservation professional determines the actual limit and display duration.

Step 4: Turn lux readings into an exposure log

A passing lux reading is only the start. To estimate cumulative exposure, multiply the illuminance at the object by the hours that object is lit. For example, 80 lux × 6 hours per day × 90 days = 43,200 lux-hours, or 0.0432 Mlx h. This is an arithmetic example, not a safe exposure allowance. The allowable dose depends on the object’s sensitivity and the institution’s policy.

Use actual lighting hours where possible. Public opening hours may omit private events, cleaning, photography, testing and lights left on after closing. If different scenes expose the object to different levels, calculate each period separately and add the results. For example, a low public scene and a short installation scene should not be collapsed into one unrecorded average. A logger or control-system record can help when schedules vary.

Keep the dose record attached to the object and exhibition history. When a work moves to another wall or returns for a later show, staff can see prior exposure and review the new plan. CCI’s guidance for paper objects recommends monitoring and recording light and UV levels and keeping cumulative light-exposure records, especially for highly sensitive items. The log should remain understandable after the original installer has left the project.

Step 5: Check ultraviolet and daylight separately

Do not describe an LED installation as “UV-free” without measuring or obtaining valid data for the exact light source and arrangement. CCI recommends measuring light and UV levels for new exhibitions and using filters on UV-emitting sources. It also explains that UV and visible light are different risks: controlling UV does not cancel visible-light fading. Request model-specific information from the supplier and measure the installed condition when the conservation plan requires it.

Daylight can dominate a carefully dimmed electric-light scene. Check for direct sun at different times of day and year, reflections from adjacent surfaces, and the effect of doors or blinds. Record whether the window treatment is part of the approved lighting condition. If a shade is later removed, the old electric-light commissioning record no longer describes the full exposure. Add a follow-up check to the room’s operating procedure.

When using a UV meter, follow the instrument method and the conservation team’s protocol. CCI’s note on UV measurement describes taking light and UV readings with the sensor parallel to the object surface. Record the units correctly; an ultraviolet reading is not interchangeable with lux, and a low lux value does not prove low UV. If a source or filter is replaced, repeat the relevant measurement.

Step 6: Witness the control scenes and failure behaviour

Commission the controls in the room, not only at a desk. Confirm that the public scene reaches the recorded level, the closed scene turns off or reduces light as intended, and the cleaning and event scenes require deliberate selection. Test the installed drivers and dimmers together for stable low-output behaviour. If the system is programmed centrally, provide local staff with a clear way to identify the approved scene without encouraging unauthorized changes.

Test what happens after a power interruption or control reset. Does the gallery return to the approved scene, a maximum-output default or an unknown state? Record the answer and the corrective procedure. If individual track heads can be moved, mark their approved position or keep a photo and aiming schedule. A future rehang can then begin from a known baseline, followed by new object-plane readings.

Separately check circulation and label visibility. A strict limit at a sensitive object does not mean visitors should have to navigate an unsafe dark route. Where the design uses different light levels between a bright foyer and a dim gallery, plan a comfortable transition and assess glare from common sightlines. Conservation goals and accessible visitor experience should be signed off together.

Step 7: Document acceptance and changes

At handover, issue one record per object or display zone: object ID, location, date, responsible person, meter details, scene, daylight condition, measurement points and readings, agreed limit, action taken and final acceptance. Attach a track-head schedule, control-scene list and any photometric or UV data relied on. Photographs help locate fixtures and readings, but do not substitute for the numbers.

Agree triggers for remeasurement. Common triggers include rehanging a work, replacing a track head or driver, changing optics or shielding, updating a control scene, altering blinds or glazing, and receiving a lender with different requirements. Also set a routine inspection interval appropriate to the exhibition. A record only has value if someone can recognize when it is out of date.

A practical handover worksheet

• Object and policy: ID, material, sensitivity assessment, lender or conservator limit, planned display period.
• Location: gallery, wall or case, diagram reference, measurement points and sensor orientation.
• Lighting condition: scene name, dimmer level, track-head IDs, optics or accessories, daylight and blind position.
• Instrument: lux meter and UV meter where used, units, calibration status, operator and date.
• Results: individual readings, maximum relevant point, reflections or glare observed, corrective action and final approval.
• Exposure: actual or planned lit hours, lux-hour calculation, monitoring method and review date.
• Change control: who may alter scenes or aiming, what triggers remeasurement and where records are stored.

The lighting supplier should provide the exact fixture configuration, photometry, driver and control information needed for this process. LCB’s COB track spotlight page shows one commercial directional-lighting option; it does not establish conservation suitability for a particular collection. Confirm the proposed model’s data and test it in the actual room. Our IES and LDT photometric file checklist helps buyers request model-specific data before the mock-up. For a wider product discussion, use the LCB product range.

Frequently asked questions

Where should a lux meter be placed for a painting?

Measure in the plane of the work at representative and potentially brightest points, following the conservator’s safe handling method. Record the exact position and scene. A floor reading or a reading aimed at the lamp will not describe the illuminance incident on the painting.

Is one reading at opening enough?

No. Daylight, scene changes, fixture movement and replacement can change the result. Establish a baseline at handover, then remeasure when the exhibition or lighting condition changes and at the interval set by the institution.

How are lux-hours calculated?

Multiply the measured lux by the hours the object receives that level of light. Add separate periods when levels differ. The result is an exposure estimate, not a universal permission to display; the conservation team decides the acceptable dose.

Does a low-UV LED remove the need for exposure tracking?

No. Visible light can still fade sensitive materials. UV and visible light should be assessed separately, and lit hours should be recorded according to the object’s policy.

What should happen after a fixture or control change?

Restore the approved scene, inspect the object and visitor view, repeat the affected measurements and update the handover record. Do not assume a replacement with the same catalogue name produces the same installed result.

Sources: Canadian Conservation Institute, Light, ultraviolet and infrared; Framework for Preserving Heritage Collections; Caring for paper objects; Measurement of Ultraviolet Radiation. Collection-specific limits and handling methods belong to the responsible conservator.