Executive answer
Three different questions behind one brightness report
- A whole-area mean, an individual legend mean and an average of legend means can be different quantities.
- A legend can be internally uniform yet much dimmer than its neighbor. Define both comparisons if both matter.
- Return the marked regions, raw measurements, weights and formula with the result; a percentage without that context is incomplete.
Current guidance context
What OEM engineers and sourcing teams should decide first
Suppose two sample reports show the same average luminance. One panel has a small icon that is much dimmer than a larger legend; the other does not. Before asking which light guide or LED is better, ask what surface was averaged. A single number cannot preserve the location and size of every feature it combines.
Start the optical acceptance discussion with controlled artwork and stable legend IDs. Decide whether the requirement concerns a local patch, one complete legend, several legends intended to match, or the union of selected illuminated surfaces. These are separate evaluation regions, not interchangeable names for the entire front panel.
Name the quantity and the measured surface
CIE defines luminance with a specified point and direction and expresses it in candela per square meter, cd/m². Its average-luminance entry concerns a specified surface. Those definitions make the surface boundary part of the reported quantity: an average over an icon is not automatically the average over all icons or over the surrounding dark mask.
Konica Minolta's measurement fundamentals distinguish luminance from illuminance. Illuminance, reported in lux, describes light arriving at a surface; luminance concerns light in a specified direction from a source or secondary surface. An ambient lux reading is useful context, but it is not the legend's cd/m² result. Do not substitute one for the other in a quotation comparison.
For each region of interest, or ROI, put its ID and boundary on the artwork or measurement map. State whether edges, narrow strokes, gaps and neighboring unlit areas are included. Define the spatial resolution or measurement locations sufficiently to show which features were actually evaluated. The same region name with a different outline is a changed calculation input.
Work two records with the same overall average
This is a hypothetical HYR editorial example, not measured product data. Imagine two legends, K1 and K2, with selected emitting areas in a 9:1 ratio. Divide their union into ten equal-area surface cells: nine belong to K1 and one to K2. Exclude all dark background and gaps. Assume the same specified viewing direction, installed and drive condition, and constant luminance within each legend. No instrument error, color difference or visual-readability model is supplied.
Record A assigns 100 cd/m² to each of K1's nine cells and 10 cd/m² to K2's one cell. The area-weighted average of the union is (9 × 100 + 1 × 10) / 10 = 91 cd/m². Record B assigns 91 cd/m² to every cell. Its union average is also 91 cd/m². The reported overall averages are identical, but the per-legend means are 100 and 10 in A, versus 91 and 91 in B.
If the report instead gives each legend mean one equal vote, A becomes (100 + 10) / 2 = 55 cd/m²; B remains 91 cd/m². That 55 is an equal-weight summary of two legend means, not the area-weighted average of their combined surface. Neither calculation is arithmetically wrong when labeled correctly. They answer different questions, and switching between them without disclosure can change the comparison.
The example establishes only that aggregation can hide a selected region. It does not select an acceptable luminance or show that B is readable, comfortable, correctly colored or suitable for the equipment. For real unequal-area regions, use their actual area weights; equal image-pixel counts should not silently be treated as equal physical areas when geometry or processing changes that relationship.
Separate within-legend uniformity from cross-legend balance
CIE's luminance-uniformity entry defines Uo as minimum luminance divided by average luminance for a surface, a dimensionless quantity. State the selected surface and the exact formula beside a reported uniformity value. A report using another agreed formula must name it explicitly; do not relabel minimum/maximum as the CIE minimum/average definition.
Under the example's constant-within-legend assumption, K1 and K2 each have Uo = 1, or 100%, in both records. Yet A's small legend remains at 10 cd/m² while its large legend is at 100 cd/m². Perfect internal uniformity does not establish agreement between legends. Across the selected union, A instead has Uo = 10 / 91 ≈ 0.1099, or 10.99%; B has Uo = 91 / 91 = 1. These are different regions of evaluation, not conflicting results.
Define any cross-legend balance check separately: list each legend mean and the comparison the OEM requires. Group only functions and colors intended to be evaluated together. Do not turn deliberately different status indications into a universal demand for equal luminance, and do not use uniformity as a substitute for color, contrast or readability evidence.
Freeze the inputs before comparing suppliers
Use one marked region set for the intended comparison and retain the underlying values rather than only a rounded pass percentage. Record the sample and artwork revisions, mounting, light-source identity, drive and dimming state, stabilization, ambient condition and observation geometry. CIE's luminance entry explicitly calls for measurement conditions when an area-averaged result is reported; the project must determine its complete practical method.
Have the measurement owner state the instrument setup, calibration basis, spatial coverage, exclusions and uncertainty treatment. If a small legend cannot be resolved by the chosen measurement area, do not replace its missing result with the large neighbor's value. Agree a suitable measurement plan or leave that feature unresolved. This article does not prescribe an instrument, pixel count, distance or laboratory capability for HYR.
Keep the optical report linked to the actual stack and electrical state. The spacer and mask guide addresses where light may travel; the LED-current guide addresses who establishes the electrical drive. A changed region map can alter the report without changing the part, while a changed drive or stack can alter the part's optical behavior without changing the artwork. Record both kinds of change.
Avoid five report traps
These are hypothetical review failures, not reported HYR defects. Resolve the evidence gap before assigning a material or manufacturing cause.
- A large bright legend dominates the union mean. Keep the small legend's own result visible instead of approving it by association.
- Each legend passes an internal uniformity check, so cross-legend balance is assumed. Compare the identified legend means under the separate project rule.
- A region is trimmed to omit a dark edge after testing. Preserve the original boundary, document the proposed revision and recalculate the comparison consistently.
- Suppliers report the same percentage with different denominators or spatial coverage. Return to raw values, formulas and region maps before ranking the samples.
- A calibrated optical result is treated as complete visual acceptance. Retain the separately agreed checks for local defects, off-state appearance, color and intended-use readability.
Release a region-defined optical RFQ
Send the same controlled region map and report requirements to each quoting supplier. Ask for per-legend values, any within-legend metric, the aggregation weights and the exact formulas. Identify which missing values prevent a comparison and who will supply the measurement or representative fixture. A clearly bounded open item is more useful than an unlabeled panel average.
Before sample acceptance, the responsible OEM should connect those measurements to its own limits and visual review. Reopen the affected checks when artwork boundaries, optical layers, light sources, drive settings, mounting or measurement processing change. Keep the earlier report and accepted region-map revision so a later comparison can be reconstructed.
Use HYR's secure engineering RFQ to share the drawing, lighting states, mounting section and available optical report. The first review can clarify component scope and missing evidence without promising a specific brightness, instrument service, acceptance outcome, price or schedule.