Yèguāng Bēi (夜光杯) - or 'Luminous Glasses' - are made from minerals. You can find them in the local specialities shops (map), if you walk west from the Lanzhou Hotel, on the south side of Dōnggăng Xī Lù (东岗西路), west of Tiānshuì Lù crossing (天水路口往西走). Some of the shops in Huáng Miào (map) also sell them.