I tried this once with a dirted 5 gallon - I turned the filter off completely, so that the only equipment the tank had was the light. It didn't go well...I did get elevated CO2 levels, but ammonia levels shot up to 4 ppm and the plants melted and could not root in the substrate (presumably because the substrate became strongly anoxic, even though it was only an inch thick or so). That might have worked better if I had had a filter and surface agitation outside of the photoperiod, but I would still be careful if you try this.