Growlights: Building the Perfect Grow-Box

Looking good

Can you plumb the CO2 exhaust into the light box?

 

I know nothing about grow lights but have to share one of my Orchids was looking poorly and I moved it in to our hallway.

And I have a small table lamp in the hall and the Orchid sits beneath lamp and fr the last 3 weeks I have noticed a lot of new growth.

Its getting heat from the lamp.

 

Excellent Scrungee - really looks the job.

Of course - you will have to branch out into a whole new field of exotic plants to make the best use of it. The job has just started - not finished.

 

Do you think it will need some vents in it Scrungee ? My little grow box used to get really hot . I added louvred vents at the top and then lifted the top by about 1/2" . I may put a couple of vents in the base next year to allow for some airflow.

 

I've never liked designs which seem fully enclosed and have wondered about venting to allow heat to escape and air to get in.

The light is smaller than the box so there's a gap inside along each long side. I'm also planing to use a timber bearer spanning between the end supports to hang the light from on something adjustable like chains so there will also be a gaps at the ends.

The end panels stop 50mm short of the top framework to provide ventilation gaps and the top shelf (not yet fitted) will stop 100mm short at the back plus will sit on counter battens to provide ventilation at the front.

I haven't quite worked out lower vents yet, but was thinking of some holes in the front panel (because it's the only one not fixed and possible to work on!) with spacer blocks and Mylar covered panels to act as light baffles. Or maybe it'll be easier to have just one long slot at the bottom of it with a similar arrangement to reflect the light back in?

I'm going to conduct some tests with thermometers placed at different heights and compare them against readings taken with the front panel propped open at the bottom before making a decision on low level venting.

I've also wondered about installing a fan.

Mrs Scrungee only wants me to grow stuff we can eat!

 

I have Easy Rolls [Light Hangers] on my MH light. Works well. When I bought my Tube-rig I bought some Easy Rolls for it, but I have found that because the tube-rig is much heavier that whilst the Easy Rolls work OK, the weight makes it much more difficult to get the adjustment right, and perhaps there is a risk of the rig descending onto the plants under its own weight. So I think Chains is a better bet (for heavier rigs). (Just looked up Easy Rolls and they have a weight limit of 5kg)

Or, perhaps, construct a fixed lighting rig, and make the plants moveable towards it, rather than making the rig itself height-adjustable.

 

Got them on my two smaller T5 lights, but my new light is far to heavy for them, so it's going to be chains & S hooks. The side battens should prove useful for resting the light on whilst adjusting chain heights above.

Do these sound like a good or stupid idea for creating some air circulation in a grow box? http://www.amazon.co.uk/Solar-Energ...D0/ref=sr_1_19?ie=UTF8&qid=1355136360&sr=8-19 I wonder how long they'd last for.

 

How about a Computer Case fan? Lots of those now, to reduce noise, thermostatically reduce the speed of the fan. Although maybe the thermostat's temperature is fixed and that may not be suitable for your plants?

Did a Google ... predictably lots of info, including DIY, on the Cannabis forums ...

 

I've had to go that route as this new light doesn't (unlike my 2 smaller ones) have any ventilation holes to allow heat to rise through the unit itself, plus it chucks out a load more heat.

Luckily I had a 12v dc mains adaptor lying around (should have 2 of them) from old bits of electrical gear and about £10 bought me a 12v computer case fan from Maplin. I know I could have got it cheaper online but I wanted to see exactly what cables it had to avoid the potential problems some people have, plus I wanted it quick and to be able to take it back if I accidentally fried it if it was faulty.

My lash up works (got some info from a site called something like 'GrassBox', which surprisingly wasn't about lawnmowers), so now I'll wire it up safely, connect to an electronic timer and check out how often/long it needs to come on for to keep the temp to a reasonable level.

 

Temperature Control

I have just managed to get my light box temperature up to 35C, which is 21C higher than ambient.

Sal was kind enough recently to send me some Alocasia calidor rhizomes and some Piper nigrum (Black Pepper) seeds. On Goggling, I found that I needed a temperature of about 30C to start the Alocasia growing and 35C to germinate the seeds. Both of these temperatures were much higher that I thought I could get out of my propagator.

However the heated propagator is inside my light box. The propagator uses 22 watts and the lights in the box use 90 watts. The propagator heat is underneath the plant material, and as heat rises it will play a bigger part, watt for watt, than the light tubes that are at the top of the box.

The key to getting the temperature up was to block off all the air vents at the top of the light box, which raised the ambient temperature inside the box. I was frightened to do that in the past in case of fire. However you can do it if you monitor the temperature inside very carefully over a period of time.

I normally put both the lights and the heated propagator on a time switch. But I noticed that the temperature dropped very low overnight when they were switched off and as the house cooled, and then took several hours to come back to the normal operating temperature of 27C. So last night I left them both on overnight, and when I came down in the morning the propagator was at the normal operating temperature.

I have an ordinary propagator without a thermostat. That means it only has a low wattage heater and runs flat out when its on. Normally this will raise the temperature inside by about 5C above ambient. I added a separate thermostat a short while after I bought it. But then realised that, although it would avoid frying my seeds in late spring when ambient temperatures were high, it wouldn't help to get higher temperatures in winter because it was already running flat out when switched on. But by raising the ambient temperature inside the light box, I have found the thermostat really comes into its own. In fact I have just turned the temperature down as I think 35C may be a bit too high.

 

OK, with my customary glacial speed I have now made some tests with my light meter.

Three tests:

1) T5 Lighting rig 60cm square (brand new)

2) Metal Halide with the original bulb. Bought in Autumn 2010 it has done 2 x Winter Seasons (allowing for 8 hours per night from mid-November to end of March that is, say, 2,000 hours of running)

3) Metal Halide with a brand new bulb (I'm definitely buying a new one each season in future!)

I measured directly under the middle, at the edge of the lighting rig (in the case of T5) and then at distances from the centre point (only a single one outside the rig in the case of T5)

I repeated for various height distances from meter-to-bulb.

Its all a bit rough-and-ready. I did not attempt to get distance between meter-and-lamp accurate to the centimetre, so its approximate. No idea how accurate my meter is either, but hopefully the relative readings between the pieces of equipment are valid for comparison purposes.

T5 lighting rig (the Edge is 30cm from the centre) 8 tubes x 24W = 192W

Code:

Height Centre   Edge  +30cm
60cm    6,400  5,000  2,200
40cm   11,000  7,100  1,500
20cm   22,000  7,000    500
10cm   30,000 10,000      x
5.5cm  35,000
even closer - no significant difference

With the rig raised up, to 60cm, there is some light spill over a wider area, but (predictably for T5) the strength in the centre is weak at that height, and thus the light spill is too little to be of much use.

Needs to be used 20cm from plants, 10cm better, and has a usable area of 60cm square (0.36 m^2). Watts/sq.m. = 533

Metal Halide - old bulb

Code:

Height Centre   20cm   40cm   50cm
100cm   5,800  5,500  4,500  3,700
80cm    8,200  8,000  5,600  4,300
60cm   14,200 12,500  6,000  4,800
40cm   27,200 14,800  6,200  4,200

Metal Halide - new bulb

Code:

Height Centre   20cm   40cm   50cm
100cm  10,900 10,000  8,400  6,600
80cm   14,500 13,600 10,100  7,000
60cm   24,000 20,900 11,600  7,500
40cm   43,500 30,200  9,500  5,800

Used at 60cm height has a usable area of 80cm square (0.64 m^2), additional plants in the outer area 100cm square will benefit from light spill (1.00 m^2)
Watts/sq.m. = 625 / 400

 

OK, with my customary glacial speed I have now made some tests with my light meter.

Three tests:

1) T5 Lighting rig 60cm square (brand new)

2) Metal Halide with the original bulb. Bought in Autumn 2010 it has done 2 x Winter Seasons (allowing for 8 hours per night from mid-November to end of March that is, say, 2,000 hours of running)

3) Metal Halide with a brand new bulb (I'm definitely buying a new one each season in future!)

I measured directly under the middle, at the edge of the lighting rig (in the case of T5) and then at distances from the centre point (only a single one outside the rig in the case of T5)

I repeated for various height distances from meter-to-bulb.

Its all a bit rough-and-ready. I did not attempt to get distance between meter-and-lamp accurate to the centimetre, so its approximate. No idea how accurate my meter is either, but hopefully the relative readings between the pieces of equipment are valid for comparison purposes.

T5 lighting rig (the Edge is 30cm from the centre) 8 tubes x 24W = 192W

Code:

Height Centre   Edge  +30cm
60cm    6,400  5,000  2,200
40cm   11,000  7,100  1,500
20cm   22,000  7,000    500
10cm   30,000 10,000      x
5.5cm  35,000
even closer - no significant difference

With the rig raised up, to 60cm, there is some light spill over a wider area, but (predictably for T5) the strength in the centre is weak at that height, and thus the light spill is too little to be of much use.

Needs to be used 20cm from plants, 10cm better, and has a usable area of 60cm square (0.36 m^2). Watts/sq.m. = 533

Metal Halide - old bulb

Code:

Height Centre   20cm   40cm   50cm
100cm   5,800  5,500  4,500  3,700
80cm    8,200  8,000  5,600  4,300
60cm   14,200 12,500  6,000  4,800
40cm   27,200 14,800  6,200  4,200

Metal Halide - new bulb

Code:

Height Centre   20cm   40cm   50cm
100cm  10,900 10,000  8,400  6,600
80cm   14,500 13,600 10,100  7,000
60cm   24,000 20,900 11,600  7,500
40cm   43,500 30,200  9,500  5,800

Used at 60cm height has a usable area of 80cm square (0.64 m^2), additional plants in the outer area 100cm square will benefit from light spill (1.00 m^2)
Watts/sq.m. = 625 / 400

 

Well done Kristen - I like to see a bit of science. Though it takes a bit of working out what it all means.

The figures that pass through my mind (at plant top) are :-

600 lux - is low but plants will still grow slowly in my experience. I use this for low level overwintering.
3,000 lux - is said to be about the minimum for proper growth - I think this came from a cannabis site.
10.000 lux - is an excellent level, which is close to a summer's day. Actually peak day levels can be much higher but a constant 10,000 lux for 12 or 14 hours is almost the same. I think this also came from a cannabis site.
20,000 lux or more. I gather this is where plants tend to saturate - ie are unable to use the excess - though the figure will be dependant on what plant you are growing.

I am amazed at the loss in output of your metal halide bulb. I have never measured that for my tubes, but when I started 4 years ago I had about 10,000 lux at the plant tops, and I seem to have about the same amount now - though I have had at least one new tube during that time.

 

Very useful guidance, thanks. I'll aim for 10K

I had read, when I bought it, that I should change the bulb every year. I suppose I thought that it applied to Cannabis growers with the lamp on 24.7 for 365 days of the year - not my "8 hours a day for 3 months" scenario. However, the hassle (and additional carriage cost) of buying just one bulb meant I didn't bother. So this year I bought an extra lighting rig, some Canna fertilizer, Rooting compound ... all just so I could get free carriage for my new MH bulb!!

Pretty sure that I read that the quality of T5 light does not drop off (or not by much) over time. Several years, at least, before they need changing.

 

I had read in the past that the light output from bulbs (without being specific as to what type) dropped off with time. So I assumes that this applied to fluorescents as well. But thinking about it. The light output from a fluorescent tube is dictated by the physics of the excited gas (mercury), which in normal tubes uses 10 watts of power per foot. There is litttle you can do to change that; for instance the diameter of the tube has no effect. This is why you can't have a more powerful normal fluorescent tube - you can only make it longer to get more light. So if nothing you do will increase the light output, conversely (I presume) nothing will decrease it either. I believe tubes ultimately fail when they lose their mercury, which is slowly adsorbed by the glass and phosphors - or when air gets in.