Light testing. Long-exposure photograph showing a gonio-photometer (goniometer for short) at the Osram Sylvania Light Research Laboratory, USA. This testing device obtains measurements of light luminance over several wavelengths. The light bulb is placed at the centre of tha goniometer and its light is reflected onto a mirror located at the end of a rotating arm. Light from the mirror is in turn directed onto a sensor. The rotating arm is necessary to record light output over a large range of angles. The goniometer enables researchers to test new energy efficient long- life light bulbs.