For indoor lighting the range of space : height is

• A. 3 :4
• B. 5 : 6
• C. 2 : 3
• D. 1 : 2

Answer: (D)

In order to achieve uniform illumination over a surface, the number of luminaries must be placed suitably. The space-height ratio plays a vital role in deciding the height of lamps from floor level and their spacing.
Space to height ratio
It is defined as the ratio of horizontal distance between adjacent lamps to the height of their mountings.
In order to obtain almost uniform illumination over the working plane, the distance between the lamps should not be too much. An ideal scheme could be developed, when there is a large number of small size lamps. But this would increase the installation cost. To have uniform illumination, the ratio of the spacing between the lamps and their height above the working plane (i.e., space-height ratio) should normally lie between 1 and 2.