Overview

Under some circumstances, it is possible to receive N/A when choosing a luminaire solution.

This indicates that there are no corresponding utilization factors available for the room index and the calculation cannot be completed. Where the lumen method is not applicable, you should employ the point to point method.

Method

For certain combinations of room index and limiting space to height ratio, utilization data is no available.  The utilization data is either supplied by the manufacturer (which is rare) or calculated using the methods described in CIBSE TM5.

Part of this calculation (Table W.1) indicates that for a number of room index and limiting space to height ratio's, that there is no applicable solution. This situation is equivalent to a room containing less than one luminaire. This occurs when:

• the room index is 0.75 or less and the limiting space to height ratio is greater than 1.75
• the room index is 1.0 or less and the limiting space to height ratio is greater than 2.25