LMK Reflection: Imaging, Angle-Resolved Display Reflectance

LMK Reflection captures the full angular reflectance distribution of a display in a single image — replacing complex spot meter and goniometer setups with one fast, standard-compliant measurement. Technically, the LabSoft add-on pairs a type II-calibrated LMK luminance camera with a conoscopic lens, an automatic orientation-detection algorithm, and geometric processing into the device-under-test (DUT) coordinate system.

A conventional spot meter delivers a single integrated value for the aligned viewing direction. Goniometric scanning can produce many such values by moving the spot meter through different orientations — but each reading requires its own movement and acquisition step, so a full scan typically takes minutes to hours. In addition, every individual reading is still integrated over the spot meter's measurement field (the angular cone over which the device averages), so even at very fine scan resolution this measurement field smooths out steep reflection peaks and limits the angular detail that can ultimately be resolved.

An imaging ILMD type II instead captures all relevant viewing directions in a single exposure (seconds), and maps each sensor pixel to a much smaller angular cone — so the angular resolution is set by the camera's optical resolution and pixel size rather than by an integrated measurement spot. The result: comprehensive angular data acquired at once, finer angular detail preserved — and because the full angular distribution is visible in every shot, the operator can see directly where alignment is critical (regions with steep luminance gradients) and where it is uncritical. With a single spot meter reading this information is hidden by definition: a steep-gradient zone looks the same as a flat one, and you may be sitting on a misaligned peak without ever noticing.

The relevant display-reflection standards (ISO 15008, IEC 62977-2-2, IDMS 1.3, ISO 9241-307) were originally written assuming spot meter measurements. The imaging approach is fully consistent with their definitions and limit values — the same quantities (specular, haze, Lambertian reflectance) are evaluated, but with much richer angular data and lower setup complexity. In particular:

• ISO 15008 – legibility of in-vehicle visual displays under ambient light (minimum 2:1 contrast, geometries CID 45°/20° and IC 25°/0°, 45 klx target illuminance).
• IEC 62977-2-2 – reflectance measurements on electronic display modules.
• IDMS 1.3 chapter 11.7.3 – International Display Metrology Standard (SID/ICDM).
• ISO 9241-307 – ergonomic requirements for electronic visual displays.

A type II ILMD is calibrated photometrically (V(λ)-matched) and geometrically: every sensor pixel maps to a defined direction in space. The camera therefore delivers luminance as a function of viewing angle directly — the prerequisite for compliant CID/IC evaluation and for separating reflection contributions across the full angular distribution. Type II calibration is also available for color-capable LMK variants, so reflected color can be evaluated within the same workflow when needed.

Instead of mechanically aligning the display to the camera (mandatory with goniometer or spot meter setups), a printed or displayed test pattern is shown on the DUT. An algorithm reconstructs the geometric pose of the DUT relative to the camera and transforms each captured image live into the DUT's spherical coordinate system. This procedure minimizes alignment effort, makes switching between measurement geometries (e.g. CID ↔ IC) straightforward, and is particularly valuable for prototypes or for DUTs that lack standardized mounting fixtures — typical situations in early-stage and automotive development.

The imaging method has been cross-validated against classical reference setups. The LMK-based workflow was compared to 16 conventional spot meter / goniometric reference measurements for both the specular and the Lambertian reflectance components. The imaging results agree with the conventional references within typical measurement uncertainty. The imaging-based approach therefore delivers values that are quantitatively equivalent to the established reference methods — while at the same time providing the additional angular detail that spot meter integration cannot resolve.

The full study is available open-access via TU Darmstadt.

LMK Reflection itself captures the full angular reflection distribution in a single image. The classical components — specular, haze, and Lambertian — are then evaluated in post-processing of this data, for example with the annulus-source method demonstrated in our J-SID case study, which uses a variable-aperture source to isolate the contributions:

• Specular component — mirror-like reflection of the light source; depends on its luminance.
• Haze component — near-specular scattering around the gloss angle; depends on illuminance and on the angular subtense of the source.
• Lambertian component — diffuse, isotropic component; depends on illuminance only.

The high-resolution imaging data also makes a diffractive contribution accessible for analysis.

The pixel and sub-pixel arrangement of a display acts as a periodic micro-structure. When ambient light hits this structure, it is diffracted into discrete orders — visible as a colorful, rainbow-like pattern of bright spots outside the specular direction (most easily observed on some OLED phones under direct sunlight). This is the diffractive reflection component. Measurements with a variable-aperture source show that it scales linearly with the source luminance and depends on the angular subtense of the source — making it especially relevant for small, bright sources (the sun!) and therefore for legibility in sunlight. With an ILMD type II + conoscope, the diffractive component is captured spatially and angularly resolved in a single shot — something hardly accessible through spot meter integration.

ISO 15008 mandates a minimum 2:1 contrast for driver-relevant displays under direct sunlight (45 klx, CID 45°/20° or IC 25°/0°). LMK Reflection meets the requirement with a much faster setup than the spot meter reference method: setup without a goniometer, automatic transformation into the DUT coordinate system, and ROI-based evaluation in the driver's field of view. The method has been validated in a round-robin study with five vehicle displays across multiple labs.

LMK Reflection is available for the LMK 6 series (LMK 6-5, 6-12, 6-30) in combination with the Conoscope Compact lens.

• Monochrome variants are recommended for standards-compliant V(λ)-luminance measurements.
• Color (filter-wheel) variants additionally enable evaluation of reflected color — relevant for premium display interiors and diffractive effects.

Existing LMK 6 systems can be upgraded; please contact us for retrofit advice.

Yes. A typical example is glare assessment for photovoltaic installations (e.g. the Vienna guideline MA 37 – 476239-2022, which limits cumulative glare to < 30 h/year at defined immission points). Instead of full-angular BRDF scans on multi-axis goniometers, an imaging setup suffices — including automatic alignment via test patterns and fast switching between angles of incidence. The angle-resolved false-color images allow objective comparison of conventional and reflection-optimized PV modules.

No. The light source is characterized with the same LMK camera against a Lambertian reflectance standard. From this data, the illuminance at the DUT surface is derived — a separate illuminance meter is not strictly required.

The method has been validated in a round-robin study with five vehicle displays and multiple participating labs; each lab used a different LMK that received the same type II calibration. Reproducibility relies on factory calibration, the algorithm-based orientation detection, and a documented workflow.

The full workflow article is available open-access in Information Display Magazine.

One V(λ)-matched LMK type II covers four standards relevant for cover-material — sparkle, MTF, reflection, and ambient-contrast — by swapping lenses and configuring the geometry:

• IEC 62977-3-9 – Sparkle (standard lens)
• IEC 62977-3-6 – MTF / resolution capability (macroscopic lens)
• IEC 62977-2-1 – Reflection (conoscope lens)
• ISO 15008 – Contrast under ambient light (conoscope lens)

One platform therefore replaces several dedicated instruments for the full characterization of display cover materials (anti-glare layers, AR coatings, structured glass).