The GHRIL is a permanent facility on one of the Nasmyth platforms of the WHT. It is a large optical table on which users can set up their own instruments. It is aimed primarily at high resolution imaging, but other programmes may profit as well.
The GHRIL enclosure has a large ``optics room'' for the optical table and other equipment, and a smaller ``control room'' in which there can be a little light. They are connected by means of a revolving dark-room door. The optical table is 250 cm 135 cm and has a 2.5 cm rectangular grid of tapped (M6) holes. The WHT optical axis runs parallel to the long side of the table, about 30 cm from the edge and at a height of 15 cm. The position of the f/11 focus is on the table, about 25 cm from the front edge with the optical derotator or no derotator in place, and about 15cm from the edge with the infra-red derotator in place. Inserting or removing the derotation optics is a daytime operation.