Acceptance apertureSpecification, uncertainty, and measured needle
Unit Converters
Illuminance Tolerance Calculator
Separate the observed lux value from its uncertainty interval, retain asymmetric project tolerances, and report a guarded pass only when the full interval remains inside the specification.
ILLUMINANCE ACCEPTANCE WITH UNCERTAINTY
Test the full measurement interval against asymmetric project limits
This calculator keeps the measured lux value, entered tolerance, and expanded uncertainty separate. A guarded pass is reported only when the complete measurement interval remains inside both limits.
Decision rule: limits are inclusive. “Guarded pass” requires measured−U ≥ lower limit and measured+U ≤ upper limit. An in-band center with a crossing interval is indeterminate.
Decision—
Deviation from target—
Specification interval—
Measurement interval—
Nearest central-value margin—
Central-value state—
PHOTOMETER APERTURE
Read the measured beam and its uncertainty halo against both shutters
The green arc is the project interval; the amber arc is measured±U; the needle is the central value. This makes an in-band reading with a boundary-crossing interval visually distinct.
| Element | Lux | Decision role |
|---|
HOW TO USE
Apply a documented project rule
- Enter the target and asymmetric allowances from the governing project requirement.
- Enter the measured central value from the defined point or statistic.
- Enter expanded uncertainty in lux for that same reported quantity and coverage statement.
- Read central-value state, then the full measurement interval, then the guarded decision.
- Investigate any indeterminate or outside result with the measurement record and specification owner.
TOLERANCE FUNDAMENTALS
Six layers must not be merged
CALCULATION METHOD
Construct limits, construct the measurement interval, then decide
L = T(1−pl)H = T(1+pu)Ilow = M−UIhigh = M+UGuarded pass iff Ilow ≥ L and Ihigh ≤ H
ASYMMETRIC SPECIFICATION
Too little and too much light can have different consequences
A project may tolerate more over-lighting than under-lighting, or the reverse. Keeping the allowances independent prevents an average symmetric band from hiding the controlling side. The entered values are a project rule, not a universal recommendation.
UNCERTAINTY GUARD
A central value can pass while the supported interval does not
If measured lux lies inside the limits but measured±U crosses either boundary, the result is indeterminate under this guarded rule. That is not automatically a failure; it indicates that measurement capability, retesting, or decision policy must be resolved.
DECISION PRECEDENCE
Validate measurement scope before reporting conformity
The uncertainty value must belong to the same quantity, geometry, range, unit, and conditions as the central value. If validity fails, no pass or fail should be inferred. This page cannot judge whether the entered U or tolerance is authoritative.
DETAILED CALCULATION PROCESS
Default guarded-boundary substitution
| Symbol | Meaning | Default | Unit |
|---|---|---|---|
| T | Target | 500 | lx |
| M | Measured value | 470 | lx |
| pl | Lower allowance | 0.10 | dimensionless |
| pu | Upper allowance | 0.20 | dimensionless |
| U | Expanded uncertainty | 20 | lx |
- Lower limit = 500 × (1−0.10) = 450 lx.
- Upper limit = 500 × (1+0.20) = 600 lx.
- Measurement low = 470−20 = 450 lx.
- Measurement high = 470+20 = 490 lx.
- The central value lies between 450 and 600 lx.
- The full interval also lies inside, touching the inclusive lower boundary.
- Decision: guarded pass.
- Reverse check: interval midpoint = (450+490)/2 = 470 lx.
RESULT INTERPRETATION
Margin and decision answer different questions
Nearest central-value margin shows distance from the measured value to the closer limit. It is not uncertainty-adjusted headroom. An exact boundary can be accepted under the inclusive rule, but a different governing specification may require strict inequalities or a separate guard band.
EVIDENCE AND AUTHORITY
Retain both measurement and policy provenance
Keep target source, tolerance clause, maintained or initial basis, workplane statistic, meter, calibration, expanded-uncertainty statement, coverage factor, geometry, environmental state, timestamps, rounding policy, and the decision rule approved by the responsible party.
LIMITS AND EXCLUSIONS
What this guarded rule does not decide
- It does not calculate uncertainty from raw readings.
- It does not establish the target or tolerance.
- It does not assess uniformity, glare, spectrum, flicker, or exposure.
- It does not apply a legal or contractual conformance policy.
- It assumes symmetric expanded uncertainty around the reported value.
WORKED DECISION CASES
Same central value, different supported decisions
Capable measurement
A 470 lx result with U=20 lx fits exactly against the 450 lx lower boundary and passes the inclusive guarded rule.
Wide uncertainty
The same 470 lx with U=35 lx crosses below 450 lx. The central value remains in band, but the result becomes indeterminate.
TECHNICAL GLOSSARY
Decision terms
- Nominal target
- Declared central design value.
- Tolerance
- Permitted departure from target.
- Expanded uncertainty
- Entered interval half-width U.
- Guard band
- Deliberate decision space inside a specification.
- Indeterminate
- Evidence does not support either controlled outcome.
- Conformity rule
- Documented method mapping evidence to a decision.
- Maintained illuminance
- Value expected under defined depreciation.
- Inclusive boundary
- Equality is accepted by this rule.
IMPORTANT NOTE
Do not invent the tolerance from the measured result
Freeze the governing interval before inspecting the measurement. Post-hoc limits turn a conformity check into an untraceable justification.
Frequently asked questions
Are exact limit values accepted?
Yes, under the inclusive default rule.
Is indeterminate the same as fail?
No. It means uncertainty prevents a guarded conclusion.
Can upper and lower percentages differ?
Yes; they are intentionally independent.
Should U be standard uncertainty?
No. This field expects expanded uncertainty in lux.
Can U exceed the measured value?
Arithmetic can, but negative interval lows need method review.
Does this include uniformity?
No. Use a spatial grid calculator separately.
Who sets the target?
The governing project, standard, or responsible authority.
Does guarded pass certify compliance?
No. It applies only the entered arithmetic rule.
AUTHORITATIVE BASIS