A guide · Hospitality

Measuring light in a hotel room.

A standard lux meter can’t show melanopic light, but the body clock responds to it. Here’s how to measure a room against the published targets, and where rooms usually leak.

For owners, operators and engineering teams. Environmental guidance about the room itself; anything about a guest’s health belongs with a clinician.

Published

01 Measurement

The number that matters.

A standard light meter reads photopic lux, weighted to the cones we use for vision. The body clock responds mostly through melanopsin, a photopigment in specialised retinal cells that is most sensitive to short, blue-cyan wavelengths, around 480 nanometres.

The international standard CIE S 026 expresses that effect as melanopic equivalent daylight illuminance: melanopic EDI, in lux. Two lamps with the same lux reading can deliver very different melanopic EDI. Warmer, amber-shifted light carries less melanopic stimulus per lux than daylight-like light.

Read: CIE S 026:2018 · Brown et al., PLOS Biology, 2022

02 Expert consensus

Three published targets.

In 2022 an international expert consensus set reference targets for healthy adults. Each is measured at the eye. The day and evening targets are measured in the vertical plane at about 1.2 metres, seated eye height; the sleep target, at the sleeping position.

During the day
≥250 lux melanopic EDI
From three hours before bed
≤10 lux melanopic EDI
Sleep environment
≤1 lux melanopic EDI

The sleep environment should be as dark as possible. For activities requiring vision at night, the consensus recommends a maximum of 10 lux melanopic EDI at the eye. Visual safety and accessibility requirements take precedence; provide sufficient light for safe movement. By day, daylight comes first and electric light tops it up.

The limit: these targets are for healthy adults on a regular day–night schedule. They describe the environment. They don’t diagnose or treat anything, and they aren’t a jet-lag or night-shift protocol.

Read: Brown et al., PLOS Biology, 2022

03 Equipment

What to measure with.

Use a spectrometer or spectral light meter that reports melanopic EDI under CIE S 026. Hold the sensor vertically at eye level, facing the way a guest would look: across the desk, towards the lounge, along the bed.

An ordinary lux meter can’t give you melanopic EDI, though it can still help you find leaks. Record the room type, the time, the lighting scene and the curtain position with every reading, so the next audit compares like with like.

04 Method

Five readings per room type.

A room light audit

Five readings. Four usual leaks.

Plan of a hotel room showing where light is measured and where it leaks A room plan with five measurement points: the desk by the window, a lounge chair, the bed sitting up, the bathroom mirror and the pillow with lights off. Four common leaks are marked: corridor light at the entry door, gaps at the curtain edges, standby LEDs on the TV, climate panel and minibar, and light spilling from the bathroom. Corridor Window Bath TV Desk Bed 1 2 3 4 5 A B C D
Illustrative room plan. Readings are melanopic EDI in lux at eye level, against the consensus targets in Brown et al., PLOS Biology, 2022. Recommended maxima are 1 lux melanopic EDI at the sleeping position and 10 for activities requiring vision at night. Visual safety and accessibility requirements take precedence.
  • 1
    Desk by the window · daytimeAt seated eye height, curtains open as the room is sold. Target: at least 250.
  • 2
    Lounge chair · evening sceneThe scene a guest sees after turndown. Target: no more than 10.
  • 3
    Bed, sitting up · reading lights onThe last hour before sleep. Target: no more than 10.
  • 4
    Bathroom mirror · evening and nightIncluding any night light. Target: no more than 10 lux melanopic EDI, subject to safe visibility and accessibility.
  • 5
    Pillow · lights offDoor closed, curtains drawn, TV on standby. Target: no more than 1.

05 Common failures

Where rooms usually leak.

  • A
    Corridor lightDoor seals and a threshold strip. Test with the corridor at its brightest.
  • B
    Curtain edgesReturns or side channels on the blackout, and a pelmet or ceiling pocket at the top.
  • C
    Standby LEDsDim, cover or move indicators on the TV, climate panel, minibar and chargers. Check what’s visible from the pillow. Never cover or move smoke detectors or other life-safety devices; ask the manufacturer about low-glow options.
  • D
    Bathroom spillLow, warm night lighting in the bathroom, and a door that closes fully.

One more, and it’s a setting: evening scenes that are simply too bright. Program a turndown scene that meets the evening target and make it the default after a set hour.

06 Operations

From a measurement to a standard.

An audit tells you where a room stands. A standard keeps it there.

  • Targets by room type, written into the property or brand standard.
  • Lighting scenes programmed to the targets: day, evening and a night path.
  • A turndown routine: blackout fully closed, evening scene on, indicators covered.
  • Housekeeping and engineering checks, each with a named owner.
  • Replacement lamps specified by spectrum and output, so a repair doesn’t undo the standard.
  • A re-measure after refurbishment, and regular spot checks.
  • Results reported by room type: pass, fail, fixed.

07 Scope

What the targets can and can’t do.

The targets describe the environment, and they rest on an international expert consensus for healthy adults on regular schedules. They can’t promise any guest a better night.

Guests with sleep problems should see a licensed clinician. Travellers crossing time zones need timing advice for their journey; our guide on jet lag after long trips covers the research.