I like your plants. I didn't think you could grow tobacco like that. I also grew tomatoes indoors but I found that they didn't transplant well outside since they suffered from climate shock due to the difference in climate and died outdoors; same thing happened with cucumbers so I buy the seedlings of tomatoes to plant outdoors since it is less trouble and I grow the cucumbers in pots outdoors and transplant them when they are big enough. The problem with the mercury lamp is that it is too expensive, it consumes too much energy. Flourescent lamps are the best to use as a 26 watt lamp produces as much light as a 100 watt incadescent bulb. I actually used only a 15 watt flourescent in the fish tank and that's how I grew the seedlings. Now I transplanted them to bigger pots with a 26 watt on the ceiling. Believe it or not, I had the best results this year since I never turned the light off but left it on 24 hours a day. The plants grew twice as fast. So I feel no need to turn the light off unless I want to stunt the plants growth when they get too big.
Oh, you are really lucky. I have used a time-clock to regulate light and darkness. I have never tried 24 hours of light, because all books I read about this issue tells not to do it.
But, perhaps trying is the best way.
Perhaps I make in the near future a experiment with 24 hour light. I am very curious about the results.
This year I will be very carefull with my tabacco culture. I will grow them inside in big pots (I will have nearly 200 plants) until they are great enough to resist the evil slugs. I think about digging glasses into the earth after planted the tabacco outside and fill them with beer. The slugs will drink from it and fall drunk into the glasses
I smoke sometimes some tabacco (really not a lot), but the gouvernment takes high taxes.
Perhaps I will succeed this year.
I have a mercury lamp with the electronic. It is very bright. I can't look into it without seeing nothing for the next minutes. 18 hours a day a 400 Watt is really expensive, you are right.