A system of photometry used by the UKIRT Infrared Deep-Sky Survey. It is carried out in five broad bands and two narrow bands. The broad bands are J, H, and K (see J magnitude; H magnitude; K magnitude), together with a Z band centred on 880 nm with bandwidth 95 nm, and a Y band centred at 1020 nm with bandwidth 100 nm. This wavelength region is nearly free from lines due to the Earth’s atmosphere and lies between the traditional optical and infrared regions.