LÆFANEnvironmental monitoring
LÆFAN / Guidance / Light exposure and lux hours

Light damage is cumulative

A lux reading tells you the intensity now. A lux hour budget tells you how much exposure the object has received over time.

Visible light can cause irreversible change in sensitive materials. LÆFAN can record illuminance limits and cumulative light exposure budgets so an exhibition can be managed as an exposure problem rather than a single instant reading.

LÆFAN supports the monitoring record. It does not replace a conservator, collections policy, loan agreement or the text of a published standard.
LÆFAN environmental profile including illuminance and light exposure budget

Intensity × time

50 lux for one hour is not the same exposure as 50 lux for six months.

Light damage is cumulative. CCI guidance explains that the rate of light damage is related to intensity, while the total change also depends on the duration of exposure. That is why conservation policies often combine an illuminance target with control of exhibition time.

ILLUMINANCELux

How much light reaches the object at a point in time.

EXPOSURELux hours

A simple cumulative measure: illuminance multiplied by time.

CONTEXTMaterial sensitivity

A suitable budget depends on the object, colourants, condition and conservation policy.

Example

A budget makes the trade off visible.

An object displayed at 50 lux for 8 hours receives 400 lux hours during that day. The same object at 100 lux for 8 hours receives 800 lux hours. A cumulative budget lets the team manage brightness and exhibition time together rather than relying on a single reading.

Do not turn the 50 lux benchmark into a universal rule.

CCI describes 50 lux as a long established museum benchmark for very light sensitive material and for minimum colour vision, but appropriate exposure still depends on the object and the institution's conservation policy.

How LÆFAN handles it

Put light into the same environmental context as temperature and RH.

01Measure illuminanceCollect lux readings from a supported sensor or spot sample.
02Set a profileRecord maximum illuminance and, where used, a cumulative light exposure budget.
03Assign contextApply the profile to the location, case, sensor or campaign where it matters.
04Track exposureKeep the accumulated exposure visible over the relevant campaign or period.
05Review evidenceUse alerts and reports to show when the agreed policy was approached or exceeded.

Relevant guidance

Indoor exhibition lighting now has a current European standard.

BS EN 16163:2024 provides guidelines and procedures for choosing appropriate lighting for indoor exhibitions and includes recommendations on luminous exposure. CCI's light guidance provides accessible background on visible light, UV, sensitivity and cumulative damage.

Useful sources:BS EN 16163:2024 ↗CCI: Light, ultraviolet and infrared ↗

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