[green_fingered_ash]

What wattage per foot should i have? i've been adviced to place a 250 metal halide in an area no greater than 2x2ft= 62.5watts per ft

is it possibly to stretch this further to perhaps 2.5x2.5ft= 40watts psf

i will only be using this in the spring when its to cold to start things that may take a while, to give them a boost in growing (vs the dim  sunlight they recieve from the spring sun)

the bigger i can make the box the more i can fit in there however, theres no point i can grow more plants but in a weaker state.

waits for your advice

[DD.]

I'm sorry, but to me seems is a sledge-hammer to crack a nut.

I have no problems starting things early using nothing more than polythene bags as a propagator and aluminum foil behind the seedlings to reflect light back at them, nearly doubling the intensity of the sunlight.

[NigelB]

40Watts per sq ft is fine Green_fingered_ash. And you can use either an MH or HPS bulb, both to good effect.
Much less and your seedlings will tend to 'stretch' somewhat, trying to get nearer the light.
Just make sure you're supplying enough fresh air though, which is probably the most important thing, as things can get awfully stuffy in a box with a bulb in it.

D.D.
Chill mate. Loads of people grow in boxes.

[green_fingered_ash]

I've actually just thought how much it would cost me in total and the result is £80 just to start some seeds seems a bit to much

i do have an envirolite sitting round some place not being used (for another project that didnt get started)

maybe i will just use that, build a cheap frame() and put it in my shed to start some plants shouldnt cost more than £20 (most likely just £10) once the envirolite breaks i will just use the good old fasioned sun to power growth

[Bluedave]

thought I was on the wrong forum then - would use MH or MV lighting to grow plants underwater in my fishtanks, lol.

Plants grow well underwater with a 125 MV or 150 MH per 2' by 2' area and thats postioned at about 3' from the bottom of the tank. Considering how much light is lost as it travels through the water I would have thought that 40 W/sf would be plenty? I would think your bigger problem would be overheating?

[NigelB]

I've actually just thought how much it would cost me in total and the result is £80 just to start some seeds seems a bit to much

i do have an envirolite sitting round some place not being used (for another project that didnt get started)

maybe i will just use that, build a cheap frame() and put it in my shed to start some plants shouldnt cost more than £20 (most likely just £10) once the envirolite breaks i will just use the good old fasioned sun to power growth

Your Envirolight may be better than the MH bulb green_fingered_ash, in that the light doesn't originate from a single point, but is emitted over the whole length of the bulb, giving a more even spread of light. Less heat too, in my experience.
What types of plant are you intending to start off in your box? There's not a great deal I can think of that will gain much from starting much earlier than usual. Maybe some chillis or ginger or something more tropical that you don't often see in our gardens or greenhouses?

[green_fingered_ash]

Ive figured out how to make a box type structure for about 30ish pounds, the only thing thats left on my mind is, can i leave the light on for 24 hours or would i need a timer?

would starting seedlings of veg in mid/late march on 24 hours then planting them out 2-6 weeks later cause any negative effects? (would the vegetables be able to acclimatise or will they just start flowering since the dark period has increased significantly, then have to revert back to vegging?

[green_fingered_ash]

ventilation is sorted

Most likely chilli's/peppers and onions will be started in this box maybe a few others if they can fit

[NigelB]

Hi again Ash,
A timer could be useful, depending on what kind of environment you are trying to re-create.
I wouldn't bother with onions though, they are plenty hardy enough to go out now and overwinter in the soil in your garden. ....
 And those Envirolights, being simple compact fluorescent bulbs, are much kinder on timers than any of the high-pressure lighting systems which tend to burn the contacts in timers with depressing regularity.
The Chillies would appreciate it though, but if cost is of any importance I'm pretty sure you could buy them much cheaper then grow them in a box over winter.
Maybe Orchids or something? But whatever you do choose to grow, temperature control is something I'd like to get right before being able to sleep. ... There is a way of wiring up a standard central-heating thermostat to control extraction fans which bring in cooler air until the thermo-switch turns them off again, but you'll have to use google or whatever to search for the instructions...

Good luck with it.