Any heat-resistant, opaque object of a suitable shape could be used to obstruct the light but tbh it's never really bothered me.

The light bulb is fixed inside the bucket, the fan underneath. I put short legs on the bottom of the bucket to assist airflow. The gauze rests atop the bucket, of course, and if I need to stack more gauzes I've used cardboard rings or, better, borrowed some cake tins with removable bases.

Really, a pictorial seems in order, especially if I've just found a dimmer switch to add to the device... I just cobbled it together with what I had and let necessity be the mother of invention.