The Bathroom Trip at 3 a.m.: How Bright, and in What Colour, a Night Light Can Be Before Its Melanopic Dose Rivals the Evening Screen
Year: 2026
Type: article
Abstract: Night lights are bought by brightness and placed by convenience, while the quantity the circadian system counts is melanopic dose — spectrum-weighted light multiplied by time. This paper computes that dose for a stated four-minute bathroom trip under three common fittings, against the dose from a stated evening of screen use, 40 lux for two hours, which totals 2400.0 melanopic lux-minutes. A low amber fitting delivers 2.2 melanopic lux-minutes, 0.09 percent of the evening's dose; a bright daylight-white fitting delivers 114.0, 4.8 percent of the evening dose in four minutes. Inverting the calculation gives a design bound: to keep a single trip under two percent of the evening dose, light at the eye must stay below 12.0 melanopic lux — 66.7 photopic lux if amber, but only 12.6 lux if daylight-white. Spectrum, not brightness, is the variable that decides which side of the bound a fitting falls on. This study is simulated, not measured.
Author: Aldred, William Alexander
Language: English
Subfield: Endocrine and Autonomic Systems
Field: Neuroscience
Domain: Life Sciences
Open Access status: green
OpenAlex ID: W7225758039
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