Growlights: Building the Perfect Grow-Box

Please remember the cost of grow light usuage in terms of electricity. Someone like Kristen uses a 400 watt MH bulb. Who is paying for her electricity? Sorry, but this gardening gone mad.

 

I do agree Lakeside. As an ex accountant, I am very aware of the cost, which is why I have a light box that uses only fluorescent tubes. I also keep plants overwinter under two more fluorescent tubes and keep my greenhouse and summerhouse frost free with an electric heater. But I use an energy consumption meter http://www.amazon.co.uk/Plug-In-Power-and-Energy-Monitor/dp/B000Q7PJGW and know precisely what the cost of each appliance is.

However, things are not always as expensive as they might appear. In my first year, keeping my summerhouse frost free over the winter used 11kWh (ie £1.60), and the second year was 13 KWh (ie £2), but the cold winter of 2010 was closer to £40. Overall my winter costs are between one and two tanks full of petrol.

If I ever feel that is expensive, I walk down the street on the day that they do the recycling and I look at the bottles of scotch and wine in the recycling boxes. As one who drinks very little - I thank the Lord that he made me a gardener instead.

 

and?

Its on for 7 hours a night on Economy-7 for, say, 4 months of the year. Whatever "waste heat" it generates goes into the house, so contributes to central heating reduction.

400W x 7 hours x 4 months x 7.31p / unit = 25 quid

It's "his"

Why?

I overwinter a range of Colocasia / Alocasia and other "tender" plants under lights which would otherwise go dormant and be a nightmare to start in the Spring. I bring on seedlings in the Spring so that I can start batches earlier, rather than trying to sow them all on 1st March and have a nightmare of congestion in the greenhouse. In a lousy-light Spring, like Spring 2012, I have stocky plants rather than elongated leggy plants more prone to disease. There are loads of other benefits ...

Its a hobby, a lot cheaper than Gym, Golf, Horse riding - you name it. If its not your bag then fine

 

Their is no such thing as MADNESS when it comes to growing plants for pleasure.
A little eccentricity perhaps but not MADNESS - IMHO,
Jenny

 

Me too.

Point to mention (and I couldn't easily tell from the blurb about the Amazon one), in case folk are thinking of getting one, is that you may want to consider the minimum wattage that the device can accurately measure.

Any of them will be fine for measuring a kettle boiling, but for a mobile phone charger (to take the other extreme) you need something capable of measuring very low wattage.

Obviously boiling the kettle once a day less will pay for charging the phone - probably for a year! - but for anyone trying to be "greener" then you may be interested in saving a few watts, as well as the kilowatts - the old "If everyone in the UK turned off a 1W device" argument.

We halved our electricity usage, over a period of a couple of years, by installing more energy efficient devices, as they expired, turning things off, putting some timers on some devices, but mostly by becoming aware of exactly how much juice the various things in the house use.

 

If £25 quid is mad, what's a greenhouse, 3 sheds, 3 polytunnels, 1 pop-up greenhouse, 3 coldframes, 2 gas heaters, 2 paraffin heaters, 3 growlamps, 2 propagators, 2 rotovators, brushcutter, chainsaw, generator, lawnmower and 0.7 of an acre? (and I'm still planning on getting metal halide lighting because we'll be saving £1,500 p.a. on horse riding when our daughter goes to Uni)

 

That's right our kid - you tell 'im !!
Jenny

 

That Mylar wallpaper isn't cheap, mind ...

 

Scrungee - with the price of Uni - it might be cheaper if your daughter went back to horse riding instead.

Kristen, by chance I have the one in the link, though I was only looking to show that various types existed. I very rarely use the wattage scale. I find by far and away the most useful is the cumulative Kilowatt Hours. I have one meter permanently attached to the heater in my summerhouse and another in the greenhouse. The cumulative scale makes sense of devices that have thermostats that turn on and off. And it works well with things like fridges and freezers - you just leave it attached for a week and get the cost for a week.

Like you I find the meter very useful - often its just a matter of education. I think the key to saving energy is in understanding, how much different devices use and where heat from the house (or greenhouse) is lost.

A long time ago I wrote a computer heating program for my house as I was fed up with people telling me about savings for houses that wasn't the same as mine. So I put all the dimensions of every wall, window, door and ceiling, internal and external into the program along with the u values of lots of different materials. With a click I could change the insulation properties for any part of my house. It worked well and told me the temperature (acurately) in every room according to what radiators were switched on. I found that for my house (and nobody elses's) I saved 20% with cavity wall insulation and 20% with double glazing. My greatest heat loss is still through the double glazing. I also found that I saved virtually nothing from insulating the roof space - inspite of claims of 40% saving. If my upstairs was kept at 70F then I would have saved quite a lot. But I don't heat my upstairs as I don't want or need to sleep in a hot bedroom. So my saving is almost nothing.

I think I would have to rewrite the program to take account of the grow lights and lightbox, that I now have in the house.

 

Interesting about the loft insulation, and the fact that at modest bedroom temperatures the dT is sufficiently low that the much-touted saving isn't realised. Hadn't thought of that before, its a good point . Perhaps loft-insulation is the cheapest form of insulation to fit though, so still may make sense?

Sorry, didn't explain the Wattage thing very clearly. My understanding is that the less sophisticated usage-meters (although not necessarily based on the price of the device, per se) will not register anything if the device plugged in is very low wattage. This can be a frustration if trying to measure phone chargers which are plugged in but with no phone attached, or when a fully charged phone is attached. Or measuring Computers / HiFi etc. on standby.

I bought a new usage-meter recently, to have just that capability, but its currently plugged in to, & recording, the circulation fan in the conservatory so can't tell you whether it will actually measure small-usage devices properly ... I'll get around to trying it soon though and I'll report back.

 

The meter, my thread was linked to, is the one that I have and it seems to be capable of recording very low currents. For instance it will record the power used by itself if nothing is plugged into it. But I know what you mean. I have two such identical meters and one says it uses more power than the other when not connected to anything else. I am sure this is not true and is simply a measure of what you said - that they are not very good at recording very low currents. But then the current used to power the meter itself would be at least 10 (if not 100) times smaller than the current used to charge a mobile phone.

 

My light meter has just arrived. It was rather fiddly at first trying to fit the battery, but after I removed the shrink wrap that covered the contacts it was a lot easier (dodgy eyesight). Design of growbox for new 1.2 x 0.6m light now finalised, materials scheduled, checked out I've already got and shopping list prepared. Must investigate rumours of 20% off at B&Q this weekend.

 

I get around 15,000 lux (isn't that about right for pot/seed tray level in a growbox?) 400mm from my new light. That's just pointing the device at the light propped up against a wall, so I don't know if it would (could?) increase if above a box lined with reflective material.

Only approx 1,000 lux (or reduced to 500 with a lace curtain up - never realised they made so much difference) just inside my study window where I site my propagators if they're not inside a growbox, no wonder I need to move the pots under lights when they've germinated.

I can see I'm going to have fun with this, but when I've stopped playing with my new toy, perhaps I should be taken readings in & outside the box to check just how long plants actually need inside?

 

Scrungee - well done - you can already see the educational value of the meter. Its quite an eye opener to see how light values vary with small changes in the siting of the meter/plant.

15,000 lux is plenty - probably more than enough. My lightbox gives around 10,000 at the plant top level, and past experience suggests that that is plenty, Plants will actively germinate, grow and flower under those conditions. The level in the room where the box is, is only 100 lux at night with the lights on. So you can get an idea of the enormous range of values.

In my hall I have a 4 ft fluorescent tube at about 6 feet. Two feet below at the top of some of the plants the level is only 600 lux. But most of the plant leaves are further away than that at the bottom of the plant, or in some cases like the Brugmansia where the tops are way above the light, which is pointing down. The purpose was just to keep plants ticking over, but even at these levels they are growing slowly, and one Brugmansia is currently in flower.

I have read somewhere that about 3,000 lux is the minimum for active growth, but that 10,000 is preferable. Somewhere above about 20,000 lux, I believe that plants saturate. ie they leaves are working flat out and can't utilise any light above that level. However all these figures vary according to the plant you are growing. Big leaf shade loving plants will be happy with much lower levels of light than sun lovers.

I found this on http://generalhorticulture.tamu.edu/lectsupl/light/light.html

A foot candle is 10 lux - so just multiply the bottom scale by 10 to get lux. I think you can take CO2 exchange as a measure of the rate of growth.

I think a plant is like a factory. One department (the leaves) only works a daylight shift making sugar by photosynthesis. It then transfers the sugar to another department (the growing points) where the sugars are burnt and the energy released is used to make plant cells - ie actual plant growth. This department doesn't need light so it can work a 24 hour shift system.

In the graph above, the light compensation point is at 4000 lux (400 ft candles). This is the point at which the cell making department is using the sugar at exactly the same rate as it is receiving it from the leaf department. However when the leaf department goes home at dusk, the cell department has no raw material to use and so must also shut down.

The solution seems to be to either have 24 hours of sunlight so both departments can work a 24 hour shift, or for the light level to be doubled to 8,000 lux so that in a 12 hour shift the leaf department can make sugar at twice the rate and store enough surplus to keep the cell department supplied 24 hours a day.

However if the light level is raised any further the leaf department, just on the day shift, will make more sugar than the cell department can use in 24 hours.

The solution to this is presumably to raise the temperature thus allowing the cell department to work harder and use up more sugar. At some point the Unions come in and call a strike for overworking the staff.

 

Hi chums.,

A lot of 'techy' stuff here, a bit beyond me in it's implicationsHowever, I plan to utilise the propagator in my greenhouse with added lighting to give me a head start with respect to growing some MASSIVE onions next year. As it stands, I plan to use a pair of 250watt CFL's above (and outside) the propagator. I'm fairly reliably informed that I should get a minimum of 15-20,000 lux, even given the fact that the plastic cover will shield some of the light. I THINK that the heat inside the propagator should be sufficient to keep them going? Any thoughts?

Cheers...Freddy