The IEC flicker observer model, or light flickermeter, is an algorithm whose purpose is to assess the severity of flicker produced by artificial lighting. Historically, it was developed by extraction from the voltage flickermeter, and it is thus based on experiments with incandescent lamps. This paper is one in a series of papers focused on verifying the light flickermeter performance for LED light sources. Flicker perceptibility (visibility) and irritability thresholds are measured in conditions taking into account peripheral vision. A new flicker irritability threshold measurement procedure is presented. The data are then compared to the thresholds indicated by the light flickermeter. The paper presents a detailed and complete verification of the flickermeter thresholds both in terms of the flicker severity measure (Pst) as well instantaneous flicker (Pinst) and brings a comprehensive understanding of what these two quantities actually represent.