Editing Stroboscopic effect (section)

=== Objective assessment of stroboscopic effect ===

==== Stroboscopic effect visibility meter ====
For objective assessment of stroboscopic effect the ''stroboscopic effect visibility measure'' (SVM) has been developed.<ref name=":0" /><ref name=":1" /><ref name=":3" /> &nbsp;The specification of the stroboscopic effect visibility meter and the test method for objective assessment of lighting equipment is published in IEC technical report IEC TR 63158.<ref name=":4">IEC TR 63158:2018 + COR 1, Equipment for general lighting purposes – Objective test method for stroboscopic effects of lighting equipment, 2018-03-19.</ref> ''SVM'' is calculated using the following summation formula:

: <math>SVM=\sqrt[3.7]{\textstyle \sum_{m=1}^\infty \displaystyle\left ( \frac{C_m}{T_m} \right )^{3.7}},</math>

where ''C''<sub>m</sub> is the relative amplitude of the m-th Fourier component (trigonometric Fourier series representation) of the relative illuminance (relative to the DC-level);

''T''<sub>m</sub> is the stroboscopic effect contrast threshold function for visibility of stroboscopic effect of a sine wave at the frequency of the m-th Fourier component (see {{section link||Visibility}}). ''SVM'' can be used for objective assessment by a human observer of visible stroboscopic effects of temporal light modulation of lighting equipment in general indoor applications, with typical indoor light levels (> 100 lx) and with moderate movements of an observer or a nearby handled object (< 4&nbsp;m/s). For assessing unwanted stroboscopic effects in other applications, such as the misperception of rapidly rotating or moving machinery in a workshop for example, other metrics and methods can be required or the assessment can be done by subjective testing (observation).

''NOTE – Several alternative metrics such as modulation depth, flicker percentage or flicker index are being applied for specifying the stroboscopic effect performance of lighting equipment. None of these metrics are suitable to predict actual human perception because human perception is impacted by modulation depth, modulation frequency, wave shape and if applicable the duty cycle of the TLM.''

==== Matlab toolbox ====
A [[MATLAB|Matlab]] stroboscopic effect visibility measure toolbox including a function for calculating ''SVM'' and some application examples are available on the Matlab Central via the Mathworks Community.<ref>Stroboscopic effect visibility measure toolbox Matlab Central.</ref>

==== Acceptance criterion ====
If the value of SVM equals one, the input modulation of the light waveform produces a stroboscopic effect that is just visible, i.e. at the visibility threshold.<ref name=":0" /> This means that an average observer will be able to detect the artefact with a probability of 50%. If the value of the visibility measure is above unity, the effect has a probability of detection of more than 50%. If the value of the visibility measure is smaller than unity, the probability of detection is less than 50%. These visibility thresholds show the average detection of an average human observer in a population. This does not, however, guarantee acceptability. For some less critical applications, the acceptability level of an artefact might be well above the visibility threshold. For other applications, the acceptable levels might be below the visibility threshold. NEMA 77-2017<ref name=":5">NEMA 77-2017: ''Temporal Light Artifacts: Test Methods and Guidance for Acceptance Criteria''.[https://www.nema.org/Standards/Pages/Temporal-Light-Artifacts-Test-Methods-and-Guidance-for-Acceptance-Criteria.aspx (link)]</ref> amongst others gives guidance for acceptance criteria in different applications.
[[File:Figure4Wiki strobo influence quantities.jpg|thumb|546x546px|Figure 3: ''Generic setup to test lighting equipment for its stroboscopic effect performance'']]

==== Test and measurement applications ====
A typical test setup for stroboscopic effect testing is shown in Figure 3. The stroboscopic effect visibility meter can be applied for different purposes (see IEC TR 63158<ref name=":4" />):

* Measurement of the intrinsic stroboscopic-effect performance of lighting equipment when supplied with a stable mains voltage;
* Testing the effect of light regulation of lighting equipment or the effect of an external dimmer (dimmer compatibility).