Workplane illuminance heatmapMeasured cells only; no interpolation
Unit Converters
Illuminance Range Calculator
Preserve the spatial position of every lux reading and distinguish an average light level from the dark-point uniformity that often governs practical usability.
SPATIAL WORKPLANE RANGE
Keep every lux reading in its measured grid position
This calculator summarizes a rectangular workplane survey without sorting away its geometry. It reports average, extremes, range, sample scatter, and minimum-to-average uniformity alongside a true cell heatmap.
Grid order: enter the first physical row left-to-right, then the second row. The reading count must equal rows×columns; no missing cell is interpolated.
Grid average—
Minimum—
Maximum—
Range—
Minimum / average uniformity—
Sample standard deviation—
MEASURED LIGHT FIELD
Locate the dark and bright cells instead of reducing them to one bar
Every cell retains its coordinate and exact lux label. Min and max pins identify the controlling locations, while the summary below distinguishes level, spread, and uniformity.
| Row | Column | Illuminance | Grid role |
|---|
HOW TO USE
Reconstruct the measured workplane exactly
- Define grid origin, row direction, spacing, workplane height, and measurement boundary.
- Enter readings row by row without sorting or omitting edge points.
- Set integer row and column counts that multiply to the reading count.
- Read the heatmap to locate dark and bright cells, then use exact ledger coordinates.
- Interpret average and uniformity under the governing sampling and maintained-condition rule.
SPATIAL FUNDAMENTALS
Six statistics describe different features
CALCULATION METHOD
Preserve geometry while computing scalar summaries
Eavg = ΣErc/nR = Emax−EminU0 = Emin/Eavgs = √[Σ(Erc−Eavg)²/(n−1)]
WHY A HEATMAP
Spatial position is the evidence a sorted chart destroys
A mean and range cannot show whether low values form a perimeter, one failed-fixture zone, an aisle gradient, or random scatter. The heatmap maps only measured cells and labels each value. It intentionally avoids smooth contours that would imply unmeasured interpolation.
UNIFORMITY
Minimum-to-average retains the controlling dark point
A high average can coexist with poor uniformity when bright cells compensate for dark ones. Uniformity rises toward one as the minimum approaches the mean. A zero mean makes the ratio undefined; a zero minimum makes uniformity zero and maximum/minimum ratios unusable.
SAMPLING GEOMETRY
The grid design governs what the statistics represent
Cell spacing, offsets from walls, task zones, obstruction, mounting height, and daylight state can change the measured population. More arithmetic cannot repair a grid that misses the controlling location. Keep the survey plan and coordinates with the results.
DETAILED CALCULATION PROCESS
Default 3×3 workplane reconciliation
| Symbol | Meaning | Default | Unit |
|---|---|---|---|
| Erc | Cell readings | 520…455 | lx |
| nr | Rows | 3 | count |
| nc | Columns | 3 | count |
| n | Total cells | 9 | count |
- Confirm 3 × 3 = 9 entered readings.
- Sum the nine values without reordering.
- Divide by 9 to obtain the grid average.
- Locate the minimum at its row and column.
- Locate the maximum at its row and column.
- Range = maximum − minimum.
- Uniformity = minimum ÷ average.
- Reconciliation: average × 9 equals the original lux sum.
RESULT INTERPRETATION
Level, contrast, and location all matter
Average describes sampled level; range and sample deviation describe spread; uniformity emphasizes the darkest cell. None states why a cell is low. Compare the heatmap with fixture positions, daylight direction, shelving, surface reflectance, and measurement sequence.
EVIDENCE AND DATA LINEAGE
Make every cell repeatable
Retain room or task-zone drawing, coordinate origin, row and column directions, grid spacing, workplane height, meter, range, calibration, orientation, source state, dimming, daylight and ambient method, timestamps, temperature, and unrounded values.
LIMITS AND EXCLUSIONS
What the grid summary does not infer
- No values between measured cells are interpolated.
- No governing grid layout or target is supplied.
- No measurement uncertainty or maintenance factor is applied.
- No glare, spectrum, flicker, or daylight autonomy is assessed.
- No cause is assigned to a dark or bright cell.
WORKED DECISION CASES
Patterns lead to different follow-up
Warehouse aisle edge
Low cells form one continuous edge beside tall storage. The spatial pattern suggests obstruction or layout, not random meter scatter.
Office daylight gradient
Window-side cells are bright and interior cells are low. The mean is acceptable, but maintained electric-light uniformity requires a controlled daylight condition.
TECHNICAL GLOSSARY
Spatial survey terms
- Grid origin
- Coordinate from which cells are indexed.
- Row-major order
- Complete one row before the next.
- Uniformity
- Minimum-to-average ratio used here.
- Workplane
- Plane of the measurement grid.
- Sample deviation
- Scatter with n−1 denominator.
- Interpolation
- Estimating values between measured points.
- Maintained condition
- Defined state after depreciation and maintenance.
- Spatial lineage
- Mapping from every value to a coordinate.
IMPORTANT NOTE
Do not reorder the list to make a cleaner heatmap
The geometry is part of the evidence. Correct the source record or grid dimensions rather than moving values to visually convenient cells.
Frequently asked questions
Why must count equal rows×columns?
Every displayed cell must have one measured value.
Can I enter one reading?
Yes; range is zero and sample deviation is zero, but spatial claims are minimal.
Is the heatmap interpolated?
No. Each colored cell is one entered measurement.
Why use minimum/average?
It retains the darkest measured point relative to the sampled level.
Can zero lux be entered?
Yes. Verify instrument and environmental conditions.
Does sample deviation measure uniformity?
No. It summarizes scatter; uniformity uses the minimum.
Can different grid spacing be combined?
Not without preserving the geometry and weighting method.
Does the page test a target?
No. This page describes the measured range and field.
AUTHORITATIVE BASIS