In this study, two psychophysical experiments, one on colour preference and the other on colour discrimination, were conducted. To investigate the colour preference for blue jeans, 27 subjects with normal colour vision were asked to rate their visual appreciation of seven pairs of jeans with a colour gradient pattern. Nine LEDs, with uniformly sampled correlated colour temperature (CCT) values ranging from 2500 K to 6500 K, were used to illuminate the jeans. These lights produced a constant illuminance of approximately 200 lux, and their colour rendering indexes were between 79 and 91. In addition, using a Farnsworth-Munsell (FM)-100 Hue Test, the blue-region colour discrimination of 42 observers was assessed for five LEDs of the same type but with different CCTs (2500 K–6500 K, 1000 K interval). The results indicate that there is an optimum CCT of 5500 K for jeans, at which observers were found to exhibit the greatest capability for colour discrimination and the highest rating for colour preference. Interestingly, a significant gender difference was found in this study, which had not been observed in our previous work with quite similar experimental settings but different experimental objects. The findings of this study should provide a deeper understanding for the lighting design of shopping malls for jeans.

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The Ising-like antiferromagnet α-CoV2O6 has received considerable interests because of stabilized 1/3 magnetization plateau around 5 K under magnetic field applied along magnetic easy c-axis. In this work, this magnetization plateau was studied by varying temperature or rotating magnetic field. As temperature decreased, this stabilized plateau collapsed, and additional magnetic transitions were observed. As a result, a rich magnetic phase diagram was constructed and extended to temperature lower than previously reported. When magnetic field moved from the c to b (or a) axis, the magnetization plateau developed with field directions and vanished finally when the field was restricted in the ab plane. An impressive observation is that this 1/3-plateau can be stabilized and remain robust even when magnetic field deviated from the c axis, accompanied by the evolutions of the magnetic moments and the critical transition fields. We suppose that the origins of these temperature and angular dependences of the 1/3 magnetization plateau are related to strong spin-orbital coupling. Indeed, electron spin resonance (ESR) measurement gives large Landé factor of 8.9, evidencing that there exists strong spin-orbital coupling.

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