Opacity is an important appearance attribute in the textile industry. Obscuring power and the way textile samples block light can define product quality and customer satisfaction in the lingerie, shirting, and curtain industries. While the question whether opacity implies the complete absence of light transmission remains open, various factors can impact cues used for opacity assessment. We propose that perceived opacity has poor consistency across various conditions and it can be dramatically impacted by the presence of a high-illuminance light source. We have conducted psychophysical experiments asking human subjects to classify textile samples into opaque and non-opaque categories under different illumination conditions. We have observed interesting behavioral patterns and cues used for opacity assessment. Finally, we found obvious indications that the high-illuminance light source has a significant impact on opacity perception of some textile samples, and to model the impact based on material properties remains a promising direction for future work.