The flour mixed with a little water and vermiculite is formed into small cakes. Your spores are mixed in with the flour / vermiculite and allowed to harden a tad before it is distributed across the upper surface of the substrate / media. Recently I have been using Almond Flour but brown rice flour works just as well.
Other media that have proven successful for Hydroponic Mushrooms are Expanded Clay Aggregate [Clay Balls]. I've heard claims of using Coco Coir with vermiculite also, which sounds feasible.
Minimal Light is required.
Only when coaxing the mycellium to develop mushrooms should they receive 5 - 6 hours daily light - no more.