Grow lights, heaters etc, on a budget

Fluorescent have to be within an inch, or max two, of the plant. Power of light falls off by the inverse square law - double the distance and you only get 1/4 of the light power. Hence long tubes tend to be preferable for seedlings as you can drop the whole lighting rig down to within an inch or two of the seedlings.

CFLs are more like a light bulb, so tend to be used with reflectors on plants of uneven height - such as over wintering plants. However, IMHO, for that scenario a Metal Halide lamp is better because it has much better canopy penetration. Metal Halide tend to be higher wattage (thus cost more to run ...) and generate heat.

For keeping winter plants on tickover then CFL would be fine, to keep them actively growing then Metal Halide better, and for seedlings I think tubes are best (all seedlings are of a uniform height [you can put individual trays/pots on upturned pots / etc. so that all plant leaves are a uniform distance from the lamps)

T5 lighting rig example


http://www.3ch.co.uk/grow-lights/fluorescent-grow-lights/clonelite-4-thin-t5-lights/prod_1493.html

(I've bought from 3CH and had good service from them)

The larger 8 long tube model is 2' x 4' - 64cm x 119cm - so 0.75 sq.m.
8 x 54W = 430Watts

My 600W Metal Halide will cover about 2 sq.m. (and do double-duty for over wintering plants with lots of leaf).

The heat from Meta Halide doesn't bother me as it contributed to the heat in the house, and in Spring it heats the poly-tunnel in the conservatory, so avoids the need for any other heating (I run the light at night)

 

Kristen - if I may expand on what you said.

A) If you have a point source, such as a bulb without a reflector, light falls off with the inverse square law as you pointed out. The reason is that the wave front is a sphere where the surface area increases in line with the square of the radius.

B) However if you have an infinitely long tube, the light falls off with the inverse (not inverse square), as the wave front is a cylinder whose area increases in proportion to the radius.

c) And if the light source is an infinite plane, ie like a very large number of very long tubes the light level never reduces, because the wavefront is an infinite plane whose area never changes with distance from the light source.

In practice what this means is that if you have a light source which is a plane, like the 4 tube array in your link above, the light will not fall off quite as quickly as you think. And if your light source is in a box with perfectly reflective sides, it will appear that light is coming not only from above but from all the sides as well, which is very close to an infinite plane.

I have a light meter and have measured how the light level falls off with distance in my light-box, and found it to be between scenarios B and C. ie if I double the distance from the light source I lose less than half the light.

My apologies for the treatise - its the physicist in me coming out.

 

Ahhh, it's all so clear to me now!

 

Kristen, thanks for that

I'm quite liking the look of the 8 tube model. I'm wondering how I could use something like that, whilst at the same time provide heat for seedlings/small plants in my unheated greenhouse? Maybe construct some kind of enclosure and use a heat mat? I had hoped somehow to utilise my 1m long propagator, but obviously the 8 tube assembly would be too big. Any thoughts?

Cheers...Freddy

 

There are shorter lighting rigs - 4 tube (narrower) and Short as well as Long (2' and 4' I think). Dunno if that helps though?

Personally rather than putting this in the greenhouse I would put it in a garage / frost free location and construct and insulated box around it (using wall-insulation like Kingspan, if that is not too dear, or failing that thick polystyrene or loft insulation (which would need some boards / batons, as it isn't rigid). The lights may well provide enough heat on their own if you go down that route (or you could put it in the house, but that depends whether you have the indoor space / willing partner!).

The seedlings won't get any natural daylight, but I don't think that matters - there isn't much from Nov-Feb ... and at beginning of March-ish you might move the whole arrangement to the greenhouse - nights will be warm enough with a bit of help (bubblewrap chucked over both lights and propagator bench?) and the seedlings will get some light during the day, and extra at night.

Actually, that bit might be overkill because a tube lighting-rig is going to be solid at the top, so no sunlight will enter from above, so it will only be around the sides, not much benefit - unless you move the lighting rig to one side during the day - that may be too much faff?? Food for thought possibly though.

My Metal Halide bulb / reflector doesn't cast much shadow and is a couple of feet above the seedlings in Spring, so the sun going round the heavens shines on the plants, so to speak, and the light is on at night. (I think tubes better for seedlings, so only mentioning it as an option). My Tomato plants, for example, noticeably more "squat" and "chunky" compared to seedlings brought on in natural light (the Tomato plants are taller, but less stretched, sorry bit hard to explain). Other things, like slow growing seedlings - Petunias, Lobelia, Coleus - definitely more advanced with the extra light. I wouldn't bother for things that will grow in a hurry anyway - Runner Beans, Ricinus, Courgettes

 

Hiya Kristen, some interesting points there.

Both the garage option and the indoor option are non-starters. I don't have a garage, and swmbo wouldn't have it indoors So, it's either the greenhouse or the shed. This means that heat will be required. I'm kinda going along the lines of building a box, with painted sides (white matt emulsion), and using a heat mat, with the lighting over. I'd be interested to know your thoughts on how long the lighting should be switched on for, and timings? I would have thought that it wouldn't want to be left on for 24 hours?

Cheers...Freddy

 

Thought there might be "other factors" !!

I'd still insulate the box, in the greenhouse, I reckon.

Flat white paint is good (from earlier discussions that is more reflective than you might think, better than cooking-foil, and not far behind Mylar - which you could use but I doubt the hassle/cost makes up for the small additional reflectivity)

Perhaps a lift-off [i.e. insulated] lid that you can put on at night?

By the by, I have a couple of old polystyrene mushroom boxes and I put them, upside down, over plants (e.g. begonias / dahlias being started off, or seeds needing high-heat to germinate) that are sat on top of the boiler - it keeps the heat in at night.

I think you need about 8 hours light a day, more won't hurt. If you can use daylight during the day (lighting rig doesn't cast shade, or is moved away during daytime) , and artificial light at night, then that is the maximum boost I reckon. The plants will want some night - but midwinter lights being on from midnight to 8am will still give them darkness from 4pm to midnight.

or you could have two batches and "move" the light between the two for a couple of 12 hour shifts. Depends how much aggro that is for you ... and how many plants it turns out that you are trying to grow on

There are mechanical "light movers" that home growers with "high value crops" use. Bit excessive (and costly) for your needs, but it might give you some ideas. (Details will on Hydroponic Supplier sites, if not ask and I'll find you a link)

Its a story I've told before, but perhaps illustrates the possible benefits:

Gardeners World in September, a couple of years ago, said "Sow Canna seeds now to flower in the first year, but they will need supplemental lighting over winter". It was on the strength of that that I bought my Metal Halide lamp. I sowed the seeds middle of September, they FLOWERED in December (no kidding about that "first year" bit!!) and set seed in January. I suspect I was lighting them longer than was strictly necessary

This photo was 8 weeks from sowing seeds:



Original thread: http://gardenerscorner.co.uk/forum/threads/grow-lights.1288/

 

P.S. Bugs are a REAL problem with Winter Indoor Gardening, so keep a close eye on that. Red Spider particularly.

 

Hiya Kristen.

Thanks for that. I'm wondering that if I rely solely on daylight, would there be enough light getting into the box during the day? I'm reasonably happy to leave the lighting on all day. Also, it would be a bit of a nuisance having to go and take the top off every morning, as it's still dark when I go to work, do-able though. Btw, I hadn't envisaged putting a lid on it, I was thinking along the lines of just having the lighting resting/supported on top. Without a lid, do you not think that it would be warm enough with the bottom heat supplied by the heat mat?

Btw, that Canna, looks VERY healthy!

Cheers...Freddy

 

Its only a question of cost Freddy. The plants probably only need 8-12 hours light a day. If you gave then 8 hours at night and they get winter-quality light during the day then that's free! I'm also not sure whether any day-time day light would reach plants under a lighting rig; I've not seen one up close, but the tubes are very close together and I imagine there is a reflector above the tubes, so that will cast a large shadow so probably only the plants around the edge will get any light during the day?

If you have two batches, and can't move it morning and evening, you could move it once a day perhaps? so the plants will get daylight one day and artificial light the next (just a thought if you have more plants than lighting-area .... IME that's a racing-cert!)

Same with the heating; if you can box the light in then you may not need any other form of heating; if that's not viable with working schedules etc. then you will potentially need more heating.

One Watt running 8 hours per day is about 4p per month. If you heating & lighting is, say, 100W then that's £4 per month ... £12 per month if you run it 24/7 (the lights you might, the heating you won't). 3 - 4 months that's £50 - I think that's a lot for a couple of square feet of growing area ... but 8 hours per day would reduce the £50-ish to £15-ish which seems more reasonable to me. Best to double check my sums though!

 

It's been ages since I did any Waldram Diagram calcs, but you aren't going to get sufficient light during the day through the top of a box.

I use a 'shift' method and use gravel trays (full of square pots) the same same as my propagators (also full of square pots) to swop everything around, up to 3 'shifts' a day reaching peak times when the plants are just getting a 'top up' over natural light levels.

 

My grow light has arrived. Its a cheapo 1ft square 15W LED array (I think I posted a link to it earlier).

I've just tried it out. Foolishly I looked straight at it very briefly, figuring that most of the light will be outside the visible spectrum. It was like looking straight at the sun

Right now, the kit is switched on, being 'soak tested' for a while to see how hot it gets. I expect not very warm at all being as LEDs don't generate heat, so only the built in mains adapter will and that shouldn't be much. The idea is, I need to find out how hot it gets just so I can work out how and where to mount it. I have an old cupboard in my utility room that I can modify as much as I like. I'm thinking I might but a metal shelf half way up and mount the light under said shelf. That way any heat generated from the lights could provide bottom heat for the shelf above, where trays could be waiting to germinate, then once they're germinated, they could go to the lower half of the cupboard under the light.

 

Standard test is to hold the back of your hand at the same distance as the plants will be; I think you have to leave your hand there for a while - a minute perhaps? If its not uncomfortable then the plants will be happy. You might want to try your hand even closer, then as the plants grow you will have a metric for how close they can get to the lights before you have to raise the lights / lower the plants.

Can you put the transformer "brick" on/under a metal shelf to recycle the heat from that? or "within" the plants enclosure, at least. Watch out for water though.

 

So far, its been on for an hour and a half and is still stone cold. No discernible difference in temperature between the light array and anything else in the room, so so far so good.

Unfortunately not, as the power unit is integral to the light array. I suspect for such low wattage its not even a transformer, but just a bridge rectifier and a voltage regulator. Very efficient, and cool.

 

All good then (provided you don't put it somewhere cold that would need the waste heat!)