LMK Reflection

Issue
Indoors and outdoors, there are many different surfaces and materials with a wide range of
reflective properties. These can be actively used in architecture and lighting design. However, there are also undesired effects, such as glare from highly reflective surfaces. One
example is solar panels on roofs or on facades, which, due to their principle of operation,
are exposed to direct sunlight at a variety of angles. In the city of Vienna, for example, a
possible impairment due to glare must be ruled out by an expert under certain circumstances
in order to obtain a permit to construct a PV system (Guideline MA 37 – 476239-2022 point
6.2). The problem quickly becomes very complex due to the wide range of different solar
cells alone, which naturally have different reflection mechanisms and properties.
Aim
The measurement of the required data for the analysis must be carried out in advance under
reproducible conditions in the dark laboratory for the corresponding solar panel(s). One possibility is to use a multi-axis goniometer to scan the complete bidirectional scattering function
(BRDF) using a light source and a spot meter. Specialized systems are available for this
purpose. However, these systems are very expensive and the measurements are time-consuming and complex. This article presents a significantly more flexible and cost-effective
method of measuring reflection properties using an imaging luminance measurement device.
Description of the innovation/»best practice«
A type-II-calibrated luminance camera (ILMD Type II) is used for reproducible measurements of such reflections. The required setup is simple and flexible thanks to an orientation
detection algorithm, making the approach well suited when switching between different
types of measurement tasks, e.g., if different angles of incidence need to be considered. In
addition, light source characteristics are easily corrected via corresponding correction measurements. This way, comprehensive data can be captured quickly. The resulting information
can then be used for further verification.
Level of realization
The presented workflow with commercially available hardware and software was validated
in a round-robin measurement.

The authors present and validate an easy-to-set up approach to measure the reflection properties of a display that can measure not only the specular, haze, and Lambertian components of display reflection, but also the diffractive component. They then research the fundamental dependencies of this fourth reflection component through a series of measurements using a variable aperture source.

We present and validate an easy-to-setup approach to measure the reflection properties of displays. It is based on a wide field of view conoscopic lens in conjunction with an orientation detection algorithm. Using this approach, we can measure not only the specular, haze, and Lambertian components of display reflection but also the diffractive component. We then investigate the fundamental dependencies of this fourth reflection component through a series of measurements using a variable aperture source and an LC and OLED display. Through these experiments, we can show that the diffractive component scales linearly with the light source's luminance and depends on the angular subtense of the light source.

The imaging luminance measurement device type II-based method is a promising way to verify the conformity of the legibility of automotive displays.