Calculate using Direct Only Method

• Select Direct Only Method from the Calculate Menu.
• Click the Calculate button.

Notice the Statistics. The Average is well below our 25 fc estimate. Why?

The Direct Only Method considers only Direct light. That is light emitted from the luminaires ONLY, as measured at each point. This does not account for any surface reflectances, therefore, interreflected light has not been considered.

Remember that the reflectances in the Room Estimator were set at 70/50/20 (ceiling/walls/floor). In a large space with relatively low ceiling, as in our project, light will bounce off of the floor, return to the ceiling and then back again to the points. And, if the luminaire has an upward component in the light distribution (ours is small), this light will bounce off the ceiling and down to the points. Walls can also have a sizable effect on points near the perimeter.

Bottom line: if the surfaces have significant reflectances, they should be considered in the computations.