Metrology for Temporal Light Modulation 20NRM01
Metrology for Temporal Light Modulation 20NRM01
Based on the models given in IEC TR 63158:2018 and IEC TR 61547-1:2020, uncertainty components, which affect TLM quantities for flicker and the stroboscopic effect, have been identified. To propagate uncertainties, from the time domain to PstLM and SVM, models have been built. Using these models, sensitivity coefficients for uncertainty propagation have been determined for various waveforms. This uncertainty analyses will be an input to calibration of TLM measurement devices. Further investigation into the models revealed shortcomings of the current definitions as well as of reference implementations of TLA metrics. At the CIE Expert Tutorial and Symposium on the Measurement of Temporal Light Modulation in Athens, Greece, October 2022, various presentations have been given, providing guidance on improved implementation of the existing TLM models. In addition, the improved models have been implemented in a luminous flux measurement setup which has been used to measure a large number of light sources for TLM.
Typical performance of measurement devices can be expressed in quality indices, which characterise how a physical effect influences the instrument’s reading. For TLM measurement devices quality indices have been defined for frequency response and dynamic range of signal. With the aim of characterising TLM measurement devices an LED-based facility has been built which will be used to assess dynamic range. A laser-based facility has been realised, and procedures to measure the frequency response of TLM measurement devices have been tested. The laser-based facility will be used to further characterise and calibrate TLM measurement devices. Quality indices can be used for instrument classification, helping prospective instrument buyers selecting suitable TLM measurement equipment.
In an experimental study, conducted in an environment illuminated with multiple light sources, image sequences at frame rates of 8 kHz and 4 kHz have been taken with RGB cameras. For each colour channel of the cameras, (namely, red, green, and blue) the TLM waveforms have been extracted for a region of interest marked in the image sequences. The results reveal the operation principle of tuneable white LED-based lamps, which consist of various types of white LEDs or RGB-LEDs. The study underlined the need to evaluate TLM by a (multi-)spectral and spatial resolved measurements.
In lab-based measurements, a set of three TLM luminance sources with patterned transmissive filters have been used to generate luminance contrast patterns which are then measured by using cameras. Doing so, limitations identified regarding the sampling theorem, resulting from the charge accumulating principle as used in most pixel-based detectors, could be addressed.
Measurements taken with an imaging luminance measurement device (ILMD), on different lamps and luminaires, demonstrated the feasibility of TLM measurements with such devices. The measurement modes used will be improved and further developed. In addition, the possibilities of using conventional cameras that provide a high frame rate mode of up to 1000 Hz, such as compact cameras or smartphone cameras dedicated for slow motion recordings, are investigated. As such cameras are widely used, this is expected to increase the uptake of results.
The investigation of the visibility of the phantom array effect has started with a literature review. Based on the literature review, the effect of temporal frequency, luminance contrast (i.e. the difference between the luminance of the light source and luminance of the background) and colour of the light source, on the visibility of the phantom array effect will be studied. Two psychophysical experiments have been designed, and the experimental protocols have been approved by the Ethical Review Board (ERB) at Eindhoven University of Technology. Both experiments use a two-interval forced-choice (2IFC) task for the observers, in which observers need to indicate in which of the two sequentially presented stimuli the phantom array effect is visible to them.
With this setup a psychophysical pilot experiment has been conducted, following the method of constant stimuli, in which predefined stimuli are presented in random order. The data is used to fit psychometric functions, which gives information about the threshold and slope of the visibility threshold of the phantom array effect, needed as prior information for more efficient adaptive procedures. Changing the modulation depth in the pair of stimuli in combination with the Quest+ method (a Bayesian adaptive psychometric testing method), enables adaptive collection of data, thus reducing the number of perceptual experiments needed. Doing so, the visibility threshold of the phantom array effect can be determined for the various lighting conditions.
A description of the setup, methods and the findings so far have been presented at the CIE Expert Tutorial and Symposium on the Measurement of Temporal Light Modulation in Athens, Greece, October 2022. The data collection for both experiments is scheduled to finish before the end of 2022. After the data collection, the data will be analysed and modelled following the recommendations given in CIE249:2022. A scientific paper will be written and submitted to a peer-reviewed journal. Depending on the experimental results, follow-up psychophysical experiments will be designed and carried out in 2023.
Publishable summary of the MetTLM project, status April 2022