Growlights: Building the Perfect Grow-Box

Sorry Kristen, I jumped to the conclusion that you were talking about Metal Halide growing. I have read it more fully and feel so ashamed as the woeful lack of checking that I am willing to take my severance pay of £450,000 and resign.

But until the cheque arrives :- I have been very happy with my light box and I wouldn't change a thing if I were doing it again.

However, I used 3 ft fluorescent tubes because they nicely covered a growbag tray. But I have since found that 3 ft tubes are no longer made. I have recently bought a spare, but if I were starting again I would have to make it longer and use 4 ft tubes. The extra space can always be used, but I would have to look around for trays to fit inside. A tray is useful as you can swivel it at right angles onto a support and then get access to the plants. If the tubes are only set a short distance above the plants, you can't remove or water the plants without removing the tray.

I put my lights inside a box with reflecting sides. That way the light level didn't fall off much with distance. I had three 3 ft long tubes (ie 90 watts) over a grow bag tray. The box was slightly larger in area as you have to be able to man-handle the tray in and out. With the plant tops 4 to 6 inches below the tubes, I had a reading of 10,000 lux at the plant top. This was a very good light level. At 90 watts, its also pretty cheap to run, so I have never considered reducing the light level or only lighting part. I have it on a time switch with 14 hours on 10 hours off. The period is just a guess at roughtly what nature would provide.

For me, the dimensions of my box were dictated by the materials that were available. A growbag tray was a good size for a base; it holds all the dirt from trays and pots placed on it. Three ft tubes were a conveniant length to light the base. And B&Q sold sheets of hardboard with a white plastic coating on one side, with a width of 2 ft. So my box was 2 ft high, using those sheets for the sides.

My lights are on a false ceiling that can be raised or lowered. In fact, because the light level doesn't drop off much with distance from the tubes, I don't bother to change it. However, its an easy facility to provide, and I would keep it for flexibility.

I have a double sized heated propagator inside the box, with a lid. If I totally remove the lid everything dries out very quickly - so most of the time the lid is on.

My false ceiling leaves an air gap around as its slightly smaller than the box dimensions. I considered this to be important, as a totally sealed box with 90 watts of lighting and another 22 watts of heated propagator could get very hot. I go away at times and leave the box on unattended for 10 or 14 days at a time and would be very worried about it getting too hot. However if I was starting again I might make provision for this air gap to be variable. I want plenty of heat when I am around, but would like to be on the safe side when away.

I am not convinced about the need to be able to accomodate taller plants. I see a light box as a tool to do one job - grow small things. When the plants get big they have to move on to the next stage - whatever that is. For me its using the house windowsills, but it could be Metal Halide lights.

I have never considered batches, as you would need extra space - and its extra work. I can leave plants, unattended, in my box for two weeks when I go away which is very convenient. And I often leave them for several days even when I am around.

 

+1, but I have seen vertical T5 lights in grow light boxes enabling stuff like very early sown onions to grow bigger and earlier.

I'm sure I forgot to previously mention the need for a waterproof top over the box if located in a greenhouse, so squally showers coming in through windows, sloshing water around on high level shelving, etc. doesn't splash over the lights and blow fuses.

 

Scrungee - I agree you can make growlight boxes any shape you like and you do need to protect the electrics..

One point I forgot to mention, is the need to keep light level and heat level in balance. I think if you have a high light level, you also need a high heat level. Without the heat the plant can't utilise the high light level, and you are wasting money. So ideally I think a light-box should be in the house. And, depending on what you are growing, extra heat would be ideal. When my house temperature is about 15C, the soil in my propagator in the light-box is about 27C. This is excellent for cuttings etc.

Likewise, if you are overwintering tender plants at relatively low temperatures, you only need a low light level.

 

I'm afraid you have misunderstood how the whole resign thing works. If you admit your mistake and resign you only get half that amount. You have to refuse to resign, and I have to threaten to sack you and then offer you double the amount if you resign, and save face ... and we both have to be members of the same Club of course . Unbelievable ain't it? you couldn't make this stuff up ...


Thanks for the description of your light box. That's just the type of input I need, and very helpful. Things like the "pulling the trays out to water and supporting them" I wouldn't have thought of (until it was too late!)

For the 4' tube issue: you can get gravel trays that are 2' square (actually 60cm so might need to allow a bit of leeway) which I think would do the trick for anyone heading down that route.

I've read a variety of rules of thumb on this, but my view is that good light in Spring won't be more than 12 hours, and 12 hours gives me "two shifts", so perhaps provide extra lumens, to make sure that 12 hours is enough, and then move the lights to do two batches (this only becomes an issue when you want to do several square metres of seedlings of course, so for the average gardener might be a non-issue - although, like Greenhouses, I suspect whatever size you have it is always too small!)

I don't think that all the plants in the 2' square will be the same height (unless all the same variety of course), so my plan is to raise the plants, rather than the lights thus presenting an even leaf canopy to the lights (at say 2" gap), rather than being able to raise/lower the lights. Any thoughts?

Interesting. I had been thinking of reptile mat that was easy to put in / remove from the grow box (i.e. when bottom heat needed). Presumably if using a clear plastic cover to seed trays that will absorb some light? Although perhaps at the stage where dome-covers are needed the plants won't be needing as much light as when they are a bit bigger/stronger and can have the dome removed?

Noted, thanks.

What the score with irrigation during such absences?

Yup, I'm with you on that. I reckon once the plants are getting too tall for the grow box (dimensions presumably allow for 12"-18" tall plants, but I think even that is getting too tall for a Grow Box) they are going to struggle (need more canopy-penetrating light - e.g. Metal Halide, or greenhouse - as you say "move on to the next stage - whatever that is.")

Good points, and I have ignored my plants under MH for several days just like you describe.

My expectation is that I will have more plants than growing area ("Kristen's Law" :D). I can buy more lights & build a larger grow box, but there is a cost assocaited. Assuming I buy a lighting rig the cost is somewhere around £100 for a 2' square area (and I doubt that just buying "fittings" will be cheaper), and that is halved if I double-batch of course (well, twice the area for the same capital spend). My calculation is that 2' square filled with 3" pots is 64 plants; 64 feels like "not many plants" based on my normal annual production!. Maybe the trick is to keep them, crowded, in seed trays as long as possible - growing strong stubby seedlings, and thus proportionate large root systems - and prick them out just as Spring arrives with both enough light and heat?

But you must grow a lot of plants, like me? and you manage OK with a 3' box?

 

An additional benefit of that (obvious point, I'm sure) is that any surplus heat goes into the house reducing central heating commensurately. (Even more so with Metal Halide - my MH lamp is 400W and most of that is output as heat!)

Particularly relevant if such supplemental lighting is only used in Winter ... and if you need to justify it to a spouse using the bullshit-baffles-brains method!

 

I only shifted mine from the house into my greenhouse after the heating went on in my greenhouse and even then that was everything sitting in 2 propagators inside the box to keep them nice and snug.

 

I think I included those in a cost comparison on one of the earlier grow light threads as they worked out fairly cheap on a £/m2 basis. I've just got Mrs Scrungee's approval to buy some extra lighting for next year, but although that one from 3CH is £259.03/m2 EDIT: £253.09/m2 and a Lightwave T5 4 tube 59cm long by 37cm wide unit from Jungleseeds (free P&P on orders over £25) is £320.43/m2, and I already have 2 of those Lightwave units, it's only an extra over cost of £29.40 to keep everything to the same modular size and standardize on tube replacement, so I'll get that order off tomorrow before she changes her mind.

Next on my wants list will be metal halides after my daughter goes to Uni next year and frees up valuable growing space.

 

I make it only £ 253.09/m2 and thus a much better deal

But I wish you hadn't scaled it up to Sq.M. Looks expensive using that unit :(

400W Metal Halide would cover 1 sq.m. (from memory) and including reflector, bulb and ballast is £72 (needs a Contactor for a timer - add £20) ... running costs of 400W rather than 8 x 24W = 192W

 

I can only get that to 72 by using 70 x 70 mm square pots (and some overlap), which is what I use. My tomato seedlings grown under lights this year were exactly as described above "strong stubby seedlings" that had vigorous root systems and were pricked out from 70mm square pots to 40 x cell trays (cut to suit), then individually into 70mm square pots. Did the same thing with chillies.

P.S. Whoops, I transposed some figures when posting the the cost/m2 of that 3CH light, but the extra over cost was correct.

 

Kristen - I am sure there is no material difference between 12 and 14 hours, so a 12 hour lighting period would be perfect on a shift system. I don't have the space and couldn't be bothered to do that.

I use my lightbox for cuttings, and you always want more space for that. But in spring its to germinate seeds. I can put 48 small square pots in the propagator, and there can be loads of seed in a pot. The problem comes once they need to be potted up, because at that point you would need 100 light-boxes. That is when they move on to stage 2 - which is everywhere and anywhere in the house they can get a bit of light. Stage 2 is not perfect.

My gap between the tubes and plant tops is more like 8 to 12 inches. As I said, if you have reflective sides the light lost sideways is reflected back and so the light level doesn't fall off much with distance. Even at this distance I am still getting 10,000 lux - which is constant for 14 hours and is roughly the equivalent of a summer's day sunshine. The peak levels outside in summer can be a lot higher but with there is also cloud and lower levels in the morning and evening that make the average lower.

That's essentially what I do. If neccessary I will remove the pots that have germinated and just leave them on windowsills. Once they have germinated they are commited and can't ungerminate. I then have space for the next batch.

 

Still an A* answer

Thanks Scrungee and PeterS, I reckon I'm all set now. Got a busy day tomorrow, but hopefully Thursday I can make an experiment with the new T5 rig, the MH lamp, and my light meter which arrived in the post today (along with ... yet MORE seed packets )

 

Well done Kristen. I am glad to hear you are getting a light meter. Mine is a bit of a luxary, but I am very pleased to have it. Its fun measuring light levels in lots of different places and under different circumstances, but above all its gives me a gut feeling of how light levels change. Because the iris in our eyes changes automatically, our own eyes can be quite misleading as a sensor.

 

I thought a light meter was going to be an indulgence, but it was only about a tenner and I thought it essential at that price. I don't particularly care if it is accurate per se at that price (it probably is) so long as it gives me some relative readings - I want to compare how much the light drops off towards the edges, and as distance increases from light-to-plants, plus the difference between T5 and MH - and a new MH bulb vs. an old one. I'm a sucker for data me! Anyways ... I'll report back with the figures.

 

Yeah I believe the fluorescents can still weld a timer over time. Saying that though, cuttings can stay under 24 hour light. I'd use 24 hour light on to root cuts.
The MH is the right spectrum for leafy growth. The colour of spring almost. Cool white tubes or a mix of warm white and cool white will be best for your grow box.
Overhaul though your set-up looks ok to me.

 

About the same cost/m2 as a brand new cedarwood greenhouse with toughened glass including installation?

I've had a change of plan and this morning bought one of these EnviroGro 8 tube 1.20 x 0.65 m mm unit from 3ch for £125 which works out at only £160.26/m2 http://www.3ch.co.uk/grow-lights/fluorescent-grow-lights/t5-8-tube-long/prod_829.html and should take 169 x 70mm (that are actually 68mm) square pots under it.

It's a bit of a beast for size, looking almost as big as sunbed lights and we had to change plans for which car to use to collect as it wouldn't have fitted in our smallest one. That £125 is the best price I can find it for anywhere, and buying from 3ch meant I could collect and avoid P&P charges. That's my Xmas present sorted for this year.

My new (and existing) lights will be located in the room where my homebrew is fermenting away and where I've got the central heating on a nice steady 18 deg C (the CO2 from the fermentation process will be beneficial to the plants), but some or all of my lights will go into my greenhouse when the heating goes on.