In theory maybe, however this is not practical in reality as it quickly becomes very complicated. You would have to double the nutrients and co2 to maintain balance which have limits, light intensity isn't linear, etc.
If you eat twice as much one day and nothing the next, will you be healthy?
Your body--and the plants--are limited in what they can utilize and produce in a given time. Doubling the light available won't increase the plants ability to USE the light. Might burn them though.
I'm thinking of mounting a new (2nd) light to shine horizontally into tank when I'm not at home then reducing the light from on top when I'm home. Althis to minize light on the sand where nasty stuff grows.
Won't work. Cyano uses light, but will grow without it. You'll make your existing plants grow in strange directions (and potentially mess with the fish, since they orient themselves based on the light).
Is this the tank in your avatar? I only see a couple plants...a sword? & ? Most plants can get by on 6 hours if "everything" is in balance, CO2, ferts etc. What size tank with what lights & plants? Water parameters?