A/an ______ system utilizes luminaries which send most of the light downwards directly on the working plane but a considerable amount reaches the ceilings and walls also.

Correct option is C

Semi direct system use luminaries that send most of the light directly down to the work surface. But a substantial amount also reachs the roofs and walls.

In semi-indirect lighting system, the bulb is opaque at the bottom and a semi-transparent glass lid is used at the top along with a semi-circular reflector. In which 60%
to 90% of the light passes toward the celling.