light
Let an agent reason about light as a measurable condition of a place that enables or prevents other work, rather than as an on-off property of a lamp.
Research draft, second pass
A second pass drafted this model: the structure a model of this thing needs, and what is known about it in the world. The line under this one says how the second half was obtained - researched against sources, or recalled without web access, in which case nothing here was read anywhere and every claim is a lead to verify. Unreviewed either way.
written by Claude from model knowledge without web access - no source was read, every claim is a lead to verify
Researched by: Claude
Purpose and description
Let an agent reason about light as a measurable condition of a place that enables or prevents other work, rather than as an on-off property of a lamp.
Electromagnetic radiation in the range the human eye responds to, and by extension the illumination a place has and the fittings that produce it.
What it is for: Making things visible, and beyond that: signalling, growing plants, disinfecting, carrying data and setting the rhythm of a day.
It can be see by it, which is what almost every requirement about it is really about; measure it, at a point and on a surface; produce it, block it, filter it and reflect it; be harmed by it - glare, ultraviolet, laser exposure; signal with it, which is a different use with different requirements.
Distinguishing features
A condition of a place at a time, not an object, so it is measured rather than possessed
The source, the illumination and the perception are three different things routinely called light
Requirements are stated on surfaces and tasks, not on lamps
What it looks like
Not a thing seen but the condition of seeing. What is observed is a source, a lit surface or a shadow.
Physical character
illuminance: 0.1-100000 lux - from moonlight to direct sun; workplaces are typically 300-750
colour temperature: 2000-6500 K
colour rendering index: 60-100 Ra - matters wherever colour judgement is part of the task
visible wavelength: 380-750 nm
How it is recognised
Colour temperature, judged against a known white, separates daylight from most artificial sources
Flicker, visible in a camera or in peripheral vision, identifies the driver rather than the lamp
The distinction between illuminance on a surface and luminance of a source is invisible and constantly confused
Related models
is produced by - the fitting is a device; the light is a condition
is a condition of - requirements attach to places and tasks
is confused with - watts describe consumption, lumens describe output, and they are not proportional across technologies
regulated by - minimum levels for tasks and escape routes
In practice
Families and kinds
by source: daylight, incandescent, fluorescent, LED, discharge, laser
by purpose: general, task, emergency, signalling, growing, disinfection
by measure: illuminance, luminance, luminous flux, intensity
Identifiers
SI unit lux, lumen, candela three different quantities that are constantly substituted for one another
Standards and regulation
CIE publications, which define the photometric quantities themselves
EN 12464 and its national equivalents, which set workplace lighting levels
Emergency lighting standards, which set minimum levels on escape routes
Laser safety classification, which governs sources that can injure at a distance
Failure modes and hazards
Glare, which reduces visibility while raising measured illuminance
Flicker, which causes discomfort and can trigger seizures
Ultraviolet exposure from unshielded sources and from the sun
Light pollution and disruption of sleep and of nocturnal wildlife
Failure of emergency lighting, which is invisible until it matters
Also called
Where this came from
wikidata · CC0 1.0
Also registered as vr.tr.light-communication
Drafted structure
Bundle to layer to finding to question, as the second pass will find it: 4 bundles · 8 layers · 8 findings · 16 questions.
Quantity and measurement What is being measured, where and how.
Nearly every dispute about lighting is a confusion between four different quantities, so the model has to pin which one is meant.
Which quantity
Illuminance, luminance, flux and intensity.
Quantity and its unit
What is being claimed and in what unit.
- Which photometric quantity is being recorded here, in what unit? definition
- On what surface or in what direction was it measured? measurement
Measurement conditions
Position, time, orientation and what else was on.
Conditions of the reading
What has to travel with a reading for it to mean anything later.
- Where, when and under what conditions was this reading taken? provenance
- What would change the reading without changing the installation? boundary
Purpose and adequacy Whether there is enough light for what is being done.
Light is adequate for a task or not; a level with no task attached cannot be judged.
Task requirement
What the activity needs.
Required level for the task
The requirement, its source, and the task it assumes.
- What level does the task performed here require, and under whose standard? definition
- What happens to the requirement when the task changes? boundary
Adequacy and uniformity
Whether the level is met everywhere it matters.
Adequacy across the space
Coverage, uniformity and the worst point rather than the average.
- Is the requirement met across the space, and where is the worst point? measurement
- What must an agent do where the level is met on average but not where the work happens? action
Quality and comfort Whether the light is fit to see by, not just bright enough.
Illuminance can be met while the space is unusable through glare, flicker or poor colour rendering.
Glare and flicker
The two failures that raise complaints while meeting the numbers.
Discomfort factors
What makes adequate light unpleasant or unsafe.
- What glare and flicker are present, and how were they assessed? measurement
- Which of these must be corrected rather than tolerated, and why? action
Colour temperature and rendering
How colours appear and whether that matters here.
Colour performance
The colour properties and the tasks that depend on them.
- What colour temperature and rendering does this light have? measurement
- Which tasks here depend on colour judgement, and is the rendering sufficient for them? boundary
Safety and emergency provision Light that has to work when everything else fails.
Emergency lighting is the only lighting whose failure is invisible until the moment it is needed, so it is tested rather than observed.
Emergency provision
Escape routes, duration and testing.
Emergency lighting duty
What must be lit when power fails, for how long.
- What emergency lighting is required here, at what level and for what duration? definition
- When was it last tested, by whom, and what did the test show? provenance
Radiation hazard
Sources that can injure.
Hazardous sources
Ultraviolet, infrared and coherent sources present.
- Which sources here can cause injury, and at what exposure? boundary
- What protection or exclusion does that require, and of whom? action
What the second pass must settle
- Should the registry model light as a condition, the fitting as a device, and the requirement as a rule - three linked models rather than one?
- How should daylight be represented, given that it varies continuously and is what most requirements assume?
- What is the right way to record a lighting measurement so its position, direction and time survive with it?