Grow Lights

I saw on Gardeners World a few weeks back that the presenter was starting off some Cannas from saved-seed - on the basis that sowing them now would give him plants that will flower earlier next year. He said he would use Grow Lights to get them through the winter.

I've got 60 different varieties of somewhat-hard-to-germinate Trees, Shrubs and Herbaceous plants to germinate. I'd like to get started, particularly with those that benefit from being sown whilst the seed is fresh. Even for those that need 3 months stratification they are going to be germinating from January onwards, and getting as many as I can "done" before the vegetable germination season starts in earnest will help with my production line

A quick look on eBay has a variety of LED-type growing lights, some fluorescent tubes, and some more poncy "bulbous" type bulbs (they look like the shape I associated with Vapour [Mercury?] lights).

LED appeals on running cost grounds ...

Any experiences? what would you recommend?

Second question: Can I run the growing lights 24x7 and rotate the crops? In a two-shift system I could grow twice as many plants or use half as many lights. A 3 shift system would still give the plants 8 hours of light a day. Is that viable? (apart from the hassle of moving things around).

Would it matter if light "leaked" onto the plants not in the light? or do they need a period of actual darkness? I seem to remember they do - just want to check - if so I'm going to need to move them into another room when not under the lights, or buy a proper Cannabis growing room :D, and the ones that will have their dark-period during daylight hours will actually need a screen to keep the light out - perhaps the spare bedroom with the curtains closed will be good enough?

 

Hi Kristen
If you need to cover a large area the cheapest option would be a discharge light, metal halide or high pressure sodium. Led panels would need to be fairly close to the plants and you`d probably need a canopy of led panels the size of the area you need to cover. I use two 70w compact metal halides to cover a 6ft x 3ft area, its enough for getting a headstart on the season but not enough to grow tomatoes year round. To do that i`d need at least two 400w lights running 16 hours a day over the same area.

 

Hi Kristen. That's a good question.
I thought about grow lights to get things started early but when I Googled for it all I got was links to cannabis growing forums and all the junk in my e-mail.
But on the other hand maybe they are the experts in the business.
I still don't have any grow lights.
Will look forward to the replies.

 

Been a while now, but I did read the Cannabis forums in some detail a year or two back. I have never done Pot (whether "inhale" or not!!!) but I was amazed at the trouble the growers went to and how healthy their plants looked. At the time I was researching hydroponics as a means of propagation and it did cause me to buy-and-try an Aeroponic propagator, but to be honest the cuttings I was raising would have rooted green-fingers or not, and transplanting them from 100% humidity around their roots to soil/peat medium caused a major check, and I decided it was better just to strike things in a pot of compost like I used to do.

Hmmm ... perhaps I should go back to those forums and read up on what lighting they are using. The boys-in-Blue will be round if my electricity usage sky-rockets I expect!

"I use two 70w compact metal halides to cover a 6ft x 3ft area"

That's very helpful, thanks. I reckon 6' x 3' would give me about 200 x 3" pots. 16 hours a day isn't going to allow for 3 shifts! I make that just over 2kWh / day at, what, 13p per kWh? Call it 30p per day for 4 or 5 months ... so no more than 50 quid.

2 x 400W bulbs would be getting on for £300 over that period

 

I'll have a wander around some illicit sites and report back.

John: I was planning to do this indoors, too cold in the greenhouse I think (even for things that are hardy I want them to make some headway, so I reckon I need to give them heat as well as light, but it could be right next to the window)

 

Hi Kristen


The picture above is of a light box that I made myself three years ago. I did quite a bit of research at the time - but can't find the notes that I wrote, so I am writing from memory. Like you I looked at Marijuana growing sites and at an American 'Growing under lights' forum.

The key thing is the light level - it needs to be about 2,000 or more lux. I found that I could get that with three, three feet, 30 watt fluorescent tubes (ie 90 watts) over a growbag tray. I think that is very similar to Hex's figure. The lights were attached to a ceiling that could be lowered or raised. Ideally the lights need to be about 2 inches above the top of the seedlings or cuttings. If you double the distance you halve the light level, and I have measured this effect as last year I bought myself a decent light meter. I did write a thread on both the light box and the light meter, but the search facility seems to have difficulty in finding them.


There are expensive specialist lights, but I found that ordinary fluorescent tubes were much the cheapest to buy and to run. The running cost was about £5 per month. And they seem to work well. I have sown Salvia coccinea seeds in October and found the resulting plants in flower (in the box) in early January! I made the box with white plastic coated sheets of hardboard from B&Q on a 2" by 2" frame to keep the light in. If the box does not have reflective sides it will lose a lot of light, and you either have a lower light level or need to spend more money on stronger lights. I don't think there is any benefit in having the box near the window. The fluorescent lights will give out 2000 lux, but daylight, inside a room, may only be about 200 lux, and its very dependant on the position. So I suspect that you will lose more light from a box without sides than you will receive from daylight.

The box is inside my house, and has a heated propagator in it. This means that the temperature can be up to 25C, which with the high light level is just like a summers day. The light level of 2000 lux is low compared with a midday summer light level outside of 10,000 lux or more, but it is constant for 14 hours a day (on a time switch), unlike daylight.

I am sure you could have two shifts of 12 hours each - but I wouldn't fancy all that work of moving plants about. Whilst I believe that plants like a rest at night, they don't get complete dark for any part of the day if they grow near the Artic Circle in summer - so complete dark is probably not critical.

Just found one thread from earlier http://www.gardenerscorner.co.uk/forum/light-box-t2906.html?t=2906&highlight=lightbox

 

That's really helpful, thanks. Just looked at some Canna seeds that I soaked over the weekend and then, not having any plan!, put in a ramekin with some damp kitchen paper on Monday. They've chitted already, so I'd better get my skates on!

Good point about window-light not being much cop, and thus having a fully enclosed, reflective, box. My thought was to have the plants on a table and the light-frame on castors, so I could just wheel if from Night to Day section. The dinning table would be the perfect size - what do you think? :D

 

Wheeling the lights would be a good solution to having a shift system.

I was reading in a book on Dahlias that Dahlias (and probably many other plants) grow more at night than they do during the day. I think the mechanism is two part. Photosynthesis converts sunlight into sugars and starches absorbing carbon dioxide and giving out oxygen - but that only takes place during the day. The second process is that the sugars and starches are conveyed to different parts of the plant such as the roots, stems and flower buds, where they are burnt. Its the second burning process that helps to build plant tissue. In the burning process oxygen is taken in and carbon dioxide is given off, and this will continue day and night as long as there are enough sugars and starches to burn. This helps to explain why roots (and all parts of the plant) need oxygen and why plants give out carbon dioxide at night when there is no photosynthesis.

So going back to the plants requirement for a dark period. I suspect its more that a long daylight period is not neccessary. During strong daylight hours the plant can make enough sugars and starches to keep the internal fires going day and night. So extra daylight is not needed.

I meant to add to my previous post - that if anyone makes an enclosed box, which I feel is the most efficient way, they must leave some ventilation. Lights create heat -even fluorescent lights - and in a totally enclosed box there is a danger of fire. With some ventilation they are totally reliable and I leave my lightbox on for 10 days or more when I go away.

 

From a running cost point of view, high pressure sodium light is the way to go, having said that metal halide has a better blue spectrum for vegetative growth.
A hps produces 85–150 lumens per watt of electricity, metal halide is 65–115 lm/W and compact florescent tubes (aka energy saving bulbs) a miserable 46–75Lm/W.

Florescent tubes need to be very close to the plants, an inch or two away at most. Light intensity follows inverse square law, so doubling the distance gives you 4x less intensity. As the plants grow taller you`ll be forced to raise the light which could starve the lower leaves of light especially if they are shaded by the upper leaves.
Heat shouldn`t be an issue unless you have a lot of wattage.. you`ll only be running the lights in winter so it`ll save having to heat the room.

 

There is an interesting table here that gives the efficiency of different kinds of lamps. http://en.wikipedia.org/wiki/Luminous_efficacy And I would agree with you Hex that Sodium lamps are the most efficient. The one fact I am not sure about with sodium lamps is the effect of having all the light emitted at the same, very narrow, wavelength. Though it can't really be a problem as sodium lamps are sold as grow lamps.

I wouldn't use compact fluorescent tubes, ie long life bulbs - as Hex says they are not that efficient. But long tubes are pretty good. The problem, I understand, is that the ends of fluorescent tubes are inefficient so that the longer the tube you use the more efficient it is. I am not sure that metal halide lamps are that good. They give out a lot of light, but they also get extremely hot - which means they are using a lot of power.

Hex - you are right about the amount of light falling off with the inverse square of distance. But I think that is only true for a solitary point of light. With an infinately long tube of light, the intensity will fall off directly with distance. And if you have an infinite plane of light, the light doesn't fall off at all with distance. This is why I made a light box. It has three long tubes attached to the ceiling and as all the sides had white reflectant surfaces the light was coming from all angles. Not exactly an infinite plane of light - but my light meter was telling me that the light level did fall off slower than the increase in the distance from the tubes. ie double the distance reduced the light level by less than half. In theory if all the surfaces were perfectly reflecting the light level should be uniform throughout the entire box.

Thats a good point Hex - that the energy used is not totally lost, but helps to heat the house.

 

Hi Peter
The best type of lighting to use would depend on what you`re growing and how big its likely to get. Seedlings would get toasted under a 600w hps and a 3ft tall plant wouldn`t do well under a few fluorescent tubes. A light meter will give you the lux figure from a incandescent lamp but it won`t do a great job of growing much as the light output is mainly far red (heat). Plants make use of red and blue which is why leds make more efficient grow lights, they can be tailored for the desired wavelengths. A light meter probably wouldnt register much with them but the plants would still grow, the only issues with leds is the cost and coverage

 

Hex. I think that there is no question that LEDs are the way of the future. I have read that experimental ones can be as efficient as sodium lamps. But the ones on offer are not there yet are still pretty expensive.

I must admit I don't understand this light wavelength stuff. I read about plants using mainly red and blue light - but not green of course, which is reflected and is why plants looks green to us. But if plants just like the red and blue - how come sodium lamps are used as they are a very pure yellow, and don't overlap into the red or blue areas.

I think that long tube fluorescent lamps are the light equivalent of cheap multipurpose compost. Perhaps not the best but very economical to buy and run, and can produce some very good results. As the light given out covers a wide spectrum you don't have to worry about whether it is the right wavelength.

There seem to be two different aspects of growing under lights. One is what I do - for cuttings and seedlings. This is very effective because the plants are tiny and you can get a large number very close to the lights. The second use is for growing larger plants. As you say, to get light to the lower levels, you need much more powerful and expensive lights and you can afford to cover so few plants if they are large. I would dearly love a growing room rather than a box - but I don't think it is going to happen. :D

 

OK, I've been doing some research. You guys are spot on, thanks.

Tubes will do for vegetative growth. They need to be just an inch or two above the plant (which may be tricky as some plants grow, but I could stand the short ones on something).

Blue light is needed for growth, yellow/red for flowering / fruiting. There are specific wavelengths that the plant (Chlorophyll in particular) uses, there is some evidence that other chemical processes may use some other wavelengths. It is going to make a difference selecting light bulbs/tubes that specifically produce those wavelengths.

Light is measured both in intensity (lumens or lux) and also in the benefit that a plant will receive from it (kelvins - did he have a Brother who invented temperature? :D Actually, its referred to as the "Colour temperature" so maybe that's why they use a temperature term for measurement)

I suppose I should not worry too much about high wattage. This will only be used in winter so any heat generated will reduce central heating commensurately (although Electricity is a more expensive energy than, say, Oil or Gas for space heating, but not enough to worry about I think). In Summer the excess heat would be a nuisance at best, and cost money using air conditioning at worst - but you'd have to be smoking something to be using grow lights in Summer, right? :D

Light rigs tend to use "Easy-Rolls" or chains to adjust the height. Easy-Rolls make it easier to do by one person.

Strip light tubes are cheap enough, their fittings aren't. Why so? (There is a ballast to buy, but that doesn't look expensive, plus a metal fitting and the connectors for each end of the tube) I guess it must be the cost of the control kit. I didn't see any ballast that could control multiple bulbs - so there must be something specific to each bulb - the Ballast has to work when the bulb arcs and effectively "shorts" I suppose, and thus cannot handle multiple bulbs at once as they would arc at slightly different times. Sorry, I digress ...

I like the look of the Lightwave-T5 - various sized models, but the largest is 8 tubes (switchable to only use the middle "half"). It's 4' long x 2' wide - that would give me about 100 x 3" pots - it includes blue-spectrum lamps (red lamps also available) - for £ 175.

The T5 Lighting rig would be about 0.75m2 and 8 x 54W tubes = 432 watts

I found this, which I think is useful:

Code:

Lamp      Area     Coverage
 250 Watt 0.25m2 - 0.5m2
 400 Watt 0.5m2  - 1.0m2
 600 Watt 1.0m2  - 1.5m2
1000 Watt 1.5m2  - 2.0m2

so a 400W Metal Halide lamp would cover 1/3rd more area than the tubes Watt-for-Watt (and a 600W bulb would cover twice the area of the tubes rig, and use only 50% more energy, whereas scaling up the tubes would be pretty much linear)

So, by my reckoning, a Metal Halide unit would be cheaper to run, and they are around £85 - £110 so somewhat cheaper to buy. And if I need the light to be more yellow/red then I just need to swap the bulb for a Sodium one (indeed, there are "combo" deals which have one of each type of bulb).

I saw one unit with flexi-wings (on the reflector) which allows the width of light pattern to be adjusted - that makes sense when I have fewer plants in a small area - might as well give them more of the light.

So my inclination is to buy a 400W Reflector / bulb, and upgrade to a second light if I get too many plants for a 12-hour-shift system.

I figure I also need a Relay Timer - my Cheap+Cheerful timer is probably not going to be happy driving a 400W device with a large startup current.

So I am inclinded towards a 400W Metal Halide rather than tubes - unless you guys have some other thoughts or I've made some wrong assumptions?

P.S. on my travels around the Cannabis forums I stumbled on this post, which made me laugh
I've got a plan to make us all rich.

Some great growers on here, with a vast of experience. So why don't we all attempt growing saffron??

I'm sure we could iron out the major problems and increase yields just like we have with cannabis. Its worth its weight in gold and legal.

Just imagine the police bursting though my door and I've got a loft full off saffron haha. ​

 

You could use a hps for everything (veg and flowering) what they lose in quality (blue) they make up for in quantity. Don`t forget that even natural sunlight at dawn and dusk has a different spectrum to noon light, its the same for spring and autumn. Plants can get by quite happily on just orange/yellow hps lighting. The specialists using different lights for veg and bloom dont worry about the cost due to what they are growing
Depending on what you need to cover area and heightwise you might be better off using several smaller (250w?) lights spread out, you`d have the option of turning off the ones you did`t need at the time.
Yet another option is to use a light mover which shifts the whole light back and forth slowly on a track to cover a larger area, they also come in a circular format (imagine a giant ceiling fan with a light hanging off on each blade) its all a bit of a trade off but it can prevent hotspots forming especially with a big light.

I use ceramic metal halides, 4200K colour temperature which alledgedly provides more blue in the spectrum although the light looks "warm" once they`ve warmed up. It takes about 5 minutes from switching the light on, it sweeps through a range of colours.. getting brighter and brighter.
You`ll be needing your sunglasses in winter with a 400w