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Showing 1–30 of 1709 reference entries

Mathematics & logicExamples and counterexamples

Learn what a claim covers, explain why it works, and recognise an allowed case that shows it needs changing.

Method
Mathematics & logicCounting and zero

Count each object once, explain the final count, and distinguish quantity, position and identifying labels. Make zero’s role explicit.

Definition
Mathematics & logicNumber lines and order

Use number-line positions to compare whole numbers. Read the scale, recognise equality, and distinguish numerical distance from drawing size.

Definition
Mathematics & logicAddition and subtraction

Combine separate counts, remove a part, and find differences or missing parts. Connect objects, equations and number-line moves, then use tens and ones to regroup without changing value.

Definition
Mathematics & logicMultiplication and division

Count equal groups, distinguish sharing from making groups, and check with multiplication. Split calculations into parts; interpret zero and remainders in context.

Definition
Mathematics & logicFractions

Choose a whole, count equal fractional units, and connect sharing with division. Place fractions on the number line, including values beyond one, and explain what their numerator and denominator mean.

Definition
Mathematics & logic · Physics · MeasurementRatios and rates

Distinguish part-to-part ratios, fractions of a whole and rates with units. Scale quantities together, compare unit rates, and explain when a relationship is proportional. Check zero cases, starting amounts and whether a result fits its context.

Definition
Mathematics & logic · Physics · MeasurementQuantities and units

Describe a quantity as a numerical value with a unit, and distinguish its physical kind from its dimension. Build length, area, volume and rate units, check meaningful combinations, and separate exact unit relations from measurement uncertainty.

Definition
Mathematics & logic · Physics · MeasurementUnit conversions

Convert quantities with exact unit ratios, track cancellation through compound units, and apply the correct powers to area and volume. Distinguish temperature readings from differences, check dimensions and context, and retain measurement uncertainty when reporting.

Method
Mathematics & logic · Physics · MeasurementEstimation and uncertainty

Distinguish exact model values, rounded approximations and estimates from measurements. Declare the rounding rule, preserve information through calculations and unit changes, and interpret resolution, precision, accuracy and the stated uncertainty type without turning a report’s digits into guaranteed bounds.

Definition
Mathematics & logicVariables and expressions

Use symbols to name numbers or quantities, describe their allowed values, and evaluate expressions by replacing every occurrence consistently. Preserve grouping, signs, fractions and units, and distinguish a calculated value from solving an equation or proving two rules equivalent.

Definition
Mathematics & logicEquality and equations

Read equality as a relationship, find the permitted values that make an equation true, and justify one-step solutions by reversible operations on both sides. Work exactly with negative numbers and fractions, recognize all-solution and no-solution cases, and check the original equation, units and context.

Definition
Mathematics & logic · PhysicsCoordinates and tables

Locate a point from an ordered pair, read named axes and their scales, and connect the same values in words, tables and plots. Keep signs, fractions and units exact, distinguish an axis point from a quadrant point, and separate selected observations from a stated rule and its domain before drawing connections.

Definition
Mathematics & logic · PhysicsSlope and straight lines

Read a straight line as a stated relationship, calculate its slope from consistent signed coordinate changes, and interpret its intersections with the axes. Keep horizontal, vertical and coincident-point cases distinct, attach units and domain conditions to context models, and use numerical scales rather than appearance alone to judge a line’s change.

Definition
Mathematics & logic · Physics · MeasurementReading graphs

Read a graph’s quantities, units, ticks and context before judging its visual impression. Calculate differences, reference-based percentages and interval rates from the represented values; distinguish legitimate zoom from distorted spacing; and keep samples, interpolation, missing information, uncertainty and causal explanations separate.

Method
Physics · MeasurementObservables and measurement

Choose the physical quantity you want to investigate, specify the point, event or location involved, and explain how a reading relates to that quantity.

Method
PhysicsSystems and boundaries

Choose what belongs to an investigation, describe its condition at a stated time, and identify interactions with what lies outside its boundary.

Method
PhysicsModels and assumptions

Choose what a model represents, make its simplifications explicit, and check whether its predictions answer the physical question you actually asked.

Method
PhysicsHypotheses, laws and theories

Identify what a scientific statement does, examine its evidence and conditions, and avoid treating its name as a score for certainty.

Method
Mathematics & logic · PhysicsApproximations

Build a useful estimate, compare a correction with a stated reference scale, and check what is lost when you leave out a term.

Approximation
Mathematics & logic · PhysicsSymmetry and invariance

Specify a transformation, identify what stays unchanged, and distinguish symmetry of an object from invariance of a physical model.

Mathematical statement
PhysicsConservation laws

Use a defined system and a named quantity to track transfers, distinguish changing parts from conserved totals, and check the conditions of energy and momentum balances.

Model
PhysicsEmergence and levels of description

Choose a descriptive level, connect collective quantities with component behavior, and check when a simpler physical description answers a specified question.

Model
Mathematics & logic · PhysicsVectors

Describe displacement with fixed-axis components, combine compatible vectors, and use small exact examples to introduce span, independence, basis and real vector spaces.

Definition
Physics · Information · MeasurementScientific records

Build an inspectable physics record, test and revise a bounded cart model, preserve processing history, and plan findable data with appropriate sharing conditions.

Method
PhysicsPosition, velocity and acceleration

Describe a point's motion on a chosen straight axis, then connect signed changes, instantaneous rates and one exact set of position, velocity and acceleration graphs.

Definition
PhysicsNewton’s laws and forces

Choose one body, identify the forces acting on it, and use their vector sum to distinguish acceleration, balanced motion and mutual interactions.

Model
PhysicsWork, energy and power

Connect force and displacement to changes in motion, follow a spring’s stored energy, and distinguish an energy transfer from its rate.

Model
Physics · MeasurementSpeed of light in vacuum

c denotes the speed of light in vacuum. Its numerical value is fixed exactly in SI units.

Definition
Physics · MeasurementPlanck constant

h denotes the Planck constant. Its numerical value is fixed exactly in SI units.

Definition
DefinitionSource checked

Photometric weighting, lumen, candela, lux and luminance

MeasurementPhysics

Photometry weights radiation with a specified standard visual response.

Key knowledge

Photopic luminous flux weights spectral radiant flux by the standard V(λ) response. Luminous intensity is luminous flux per solid angle; illuminance is incident luminous flux per receiving area; luminance resolves flux per projected area and direction. Their units are lumen, candela, lux and cd/m² respectively. These quantities are not physical radiant power or a direct measurement of an individual observer’s subjective brightness.

Values and equations

Φ_v=K_m∫₀∞Φ_e,λ(λ)V(λ)dλ; I_v=dΦ_v/dΩ; E_v=dΦ_v,in/dA; L_v=d²Φ_v/(dA cosθ dΩ)

Φ_v,Φ_v,in
Luminous flux and incident luminous flux lm
K_m
Maximum luminous efficacy for the normalized standard spectral convention lm W⁻¹
Φ_e,λ
Spectral radiant flux per unit wavelength W m⁻¹
λ
Wavelength coordinate for the stated spectral convention m
V(λ)
Standard normalized photopic spectral response 1
I_v
Luminous intensity cd = lm sr⁻¹
E_v
Illuminance lx = lm m⁻²
L_v
Luminance cd m⁻²
Ω
Solid angle sr
A
Receiving or emitting area m²
θ
Angle defining positive projected area, cosθ>0 rad

Conditions and scope

  • The weighting formula uses the specified standard photopic observer, a consistently defined wavelength coordinate and its matching V(λ) function; other visual adaptation regimes require other conventions.
  • The directional derivatives and projected-area conditions follow the corresponding radiometric definitions; I_v strictly uses a point-source model.
  • K_m is the maximum efficacy associated with the chosen normalized spectral convention; it is not to be identified without qualification with the defining K_cd at exactly 540 THz.
Sources · 5

References

Sources retain their recorded scope. A source link alone does not establish verification of every statement.

  1. Photometric Calibrations, NIST Special Publication 250-95 (2018)Yuqin Zong, Maria E. Nadal, Benjamin K. Tsai and C. Cameron Miller — NISTReference guide · PDFnvlpubs.nist.govRead source
  2. International Commission on Illumination — CIE S 017:20202 sources
    1. International Lighting Vocabulary, 2nd edition: luminous fluxInternational Commission on Illumination — CIE S 017:2020Reference guidecie.co.atRead source
    2. International Lighting Vocabulary, 2nd edition: luminous intensityInternational Commission on Illumination — CIE S 017:2020Reference guidecie.co.atRead source
  3. Elementos de FotometriaGuido Stolfi · Escola Politécnica da USPCourse notes · PDFlcs.poli.usp.brRead source
  4. 国際単位系(SI)第9版 · Japanese translation, V3.01National Metrology Institute of Japan, AISTReference guide · PDFunit.aist.go.jpRead source

Evidence and review

Standard photopic weighting converts spectral radiant quantities to photometric quantities; maximum luminous efficacy and the SI defining efficacy constant have distinct roles.

2026-10-10 · Independent Chemistry, Biology and Earth/Cosmos editor (AI editorial review). Source checks and independent AI editorial review of compact reference claims, equations, units, conditions and conceptual mappings. This is not human specialist certification, laboratory accreditation, whole-book verification, or a claim that all possible foundational knowledge is present.

Foundational review

2026-10-10 · Independent AI editorial inspection of this new compact reference entry, its equations, applicability, sources and knowledge connections.

Sources from other places

Scope or convention differs

Standard-observer spectral weighting relates radiometric and photometric quantities, with luminous flux, intensity, illuminance and luminance having their distinct units.

The lecture simplifies the 683 factor; ARK distinguishes exact Kcd at the defining frequency from the spectral maximum and from subjective brightness.

Entry detailsPermanent link to this entry ↗
Record identity
foundation-measurement-photometric-quantities
Revision
foundations-audit.1
Structured reference record
Foundational core completion