Calibrating light detectors. Scientist working with a spectral responsivity facility to calibrate light detectors so that they can accurately measure infrared, ultraviolet and visible light. This machine uses a monochromator, an instrument that can be programmed to emit a narrow wavelength range of light (such as the 450-495 nanometre range for blue light). The detectors are then calibrated so that their readings match those of the standard values programmed into the monochromator. Photographed at the National Physical Laboratory in Teddington, UK.