  Light phenomena conceptual assessment (LPCA) is a conceptual survey of light
phenomena that has been recently established by the physics education research
(PER) scholars. Studying the LPCA psychometric properties is always imperative
to inform its measurement validity to potential LPCA users or beyond general
educational researchers. Classical Test Theory (CTT) and Item Response Theory
(IRT) are two popular statistical frameworks that can be utilized to explore
the LPCA measurement validity. To our knowledge, no PER studies have been
attempted to make a head-to-head comparison of those methods while validating
the LPCA. This study was the first to delineate the LPCA measurement by
statistically comparing the CTT and IRT based analysis. The LPCA dataset was
drawn from physics students of eight secondary schools presented by
Ndihokubwayo et al (2020). Our results accomplished the harmony between the CTT
and IRT arguments to estimate the LPCA item performance and students' ability
probed by the LPCA. They supported that the LPCA may be used as inventory for
evaluating conceptual understanding of light phenomena from low to high
students' ability range even some flagged LPCA items were exist based on CTT
and IRT arguments. Special considerations for further refinement related to the
discriminating power for some problematic LPCA items are discussed.
