# 03. What an engineer measures

Editorial teaching text. Check scientific claims against the cited primary sources; the project framework is identified in the text.

The box lists watts, lumens and kelvins. Each number answers a different question. Start with the task and the point where you plan to measure light.

Correlated colour temperature describes the colour appearance of white light. Sources with the same colour temperature can have different spectra. Melanopic quantities use spectral data and the appropriate spectral weighting.

Start with the measurement point. Reading requires information about the task surface; eye exposure requires a record at eye position and in the viewing direction. Record height, distances, sensor orientation and window conditions. In mixed light, a measurement describes the mixture at that point. One lamp datasheet cannot describe the mixture.

For each reading retain the date, instrument, dimming setting, daylight conditions and units. Repeat in normal working positions. A photograph does not replace a protocol, and maximum output does not describe every dimming mode. Keep unknown values empty.

Error analysis: after a lamp replacement, consumption fell by 30%, while task illumination decreased. This confirms a consumption change only. Check illuminance, glare, object visibility and temporal effects under comparable conditions. Define the service to be preserved before making an agreement.

## Key idea
Compare results obtained under equivalent measurement conditions.

## Human practice
Describe one real situation related to this topic. Separate observations from assumptions and list the evidence needed to check them.

## Agent assignment
Request the lamp specification, spectrum, dimmer compatibility and measurement report. Check units, operating mode and date.

CIE S 026:2018 · α-opic Toolbox
https://files.cie.co.at/CIE%20S%20026%20alpha-opic%20Toolbox%20User%20Guide.pdf

PLOS Biology · 2022
https://journals.plos.org/plosbiology/article?id=10.1371/journal.pbio.3001571

Light Academy · 1.5.0 · 2026-09-17