Public defence in Signal Processing and Data Analytics, M.Sc. Ville Mantela

The title of the thesis: Measurements of temporally modulated LED light sources

Thesis defender: Ville Mantela
Opponent: Dr. Carsten Dam-Hansen, DTU, Denmark
Custos: Prof. Erkki Ikonen, Aalto University School of Electrical Engineering

Unlike incandescent lamps, LED light sources require electronic components to operate, converting the alternating current of the power grid into direct current. This conversion has a significant impact on their light output, and the electronics involved often introduce unexpected variations in luminous intensity. These variations are referred to as temporal light modulation (TLM). 

When exceeding certain thresholds, TLM can have adverse effects on human health and safety. For this reason, the European Union introduced restrictions on two types of temporal light artefacts (TLA)—flicker and the stroboscopic effect—in its 2019 Ecodesign Directive. However, the practical implications of this directive have been difficult to assess, as no prior research had been conducted in this area. Moreover, the computational tools previously available for such assessments have been relatively imprecise, designed with error margins of approximately 5%. 

Traditionally, the measurement of TLA parameters has been based solely on photometric quantities, such as changes in relative luminous flux. While this approach is well suited to white lamps that can be accommodated in measurement devices, it is less effective for light sources that are more difficult to assess with conventional methods, such as recessed luminaires with non-removable light sources. 

Photometric measurements also fail to capture the influence of differently colored light sources on TLA values. Hyperspectral imaging offers a potential solution, as it enables measurement across different parts of the light spectrum, i.e. “colors” emitted by a lamp. 

The contribution of this dissertation to the study of temporally modulated light is threefold: 

• The development of enhanced computational tools, made publicly available for researchers and practitioners.
• The introduction of a novel measurement method capable of simultaneously assessing multiple light sources and determining TLA values of multicolored light sources across different regions of the spectrum.
• An empirical investigation of the directive’s impact on TLA values in commercially available white LED light sources. 

Overall, this research provides new insights into the practical implications of regulatory measures for consumers, while also delivering methodological advances and resources for both the scientific community and regulatory authorities.

Key words: flicker, stroboscopic effect

Thesis available for public display 7 days prior to the defence at Aaltodoc.