A lighting device has at least two lighting strips, which are slidable relative to each other and overlap in a region of overlap so that the overall length may be adjusted. The combined light intensity per unit length of the lighting strips in the region of overlap corresponds to the light intensity per unit length of the first and second lighting strips outside the region of overlap. This arrangement makes sure the combined light output in the region of overlap is the same as where the lighting strips do not overlap. In this way, the overall device is reversibly and repeatedly extendable and retractable and maintains a relatively constant light output per unit length.