Artificial Light over Windowsill

[dw0rk1n]

I have a great windowsill (~4.5 sq ft), but facing North (in NJ) with some trees outside. I read "Growing Cactus with Artificial Light" compilation of Ian Nartowitz's posts and would like to add some artificial light.

I am leaning toward 3 foot (or maybe 4-foot if it fits) florescent tube. It sounds like 6500K is the way to go. Or should I mix two tubes: 6500K and 2700K? If I need 20W per sq foot, then one 95W tube would be perfect? Any other considerations?

[Sutremaine]

If you can get the 4' tube and its pins between the two walls of the windowsill and still have a couple of centimetres either side, use the 4' tube. It'll be more efficient, and you'll get better light coverage.

Also, buy a light meter and check that you're getting a significant amount of tube light onto the plants. You're paying for it no matter where it ends up, so try and stop it from getting too much out the window* or onto the walls of the room.

Mixing colours is unecessary if your plants are getting full-spectrum light, and is not always necessary even in an enclosed box.

*If you can see the tube from any point on the other side of the window, that's definitely too much.

[iann]

It is generally difficult to grow cacti full time under artificial lights, and it is often pointless trying to supplement natural light because it is so easy to block more light than you add. Still, a north-facing window is really no good so I guess you have to try the lights. I can't imagine one tube being remotely enough. The natural light levels will be a tenth of what you need if you're lucky and I can't imagine you'll get more than half the fluorescent light onto the plants.

Three foot tubes aren't great. Unfortunately most four foot tubes available in the US aren't great either. For some reason the market has indulged in a chase to ever-lower powers rather than higher light output. Anything labelled 40W is probably obsolete and useless, while anything modern and efficient is likely to be 32W or even less. You might want to look for the T5HO tubes. They are marginally shorter than the classic T8 style and give a whole lot more light. 54W per tube, two tubes would be a good starting point.

Possibly there are LED tubes that would work better for you, or flat arrays. No point deliberately buying something that sprays light in all directions when it is so easy to have it all go down onto the plants. You'll have to see what's available, the market in LEDs moves so fast. They're still expensive to buy compared to fluorescents, and there are an awful lot of people basically just scamming you, but it is possible to find LEDs now that perform better than fluorescents.

[dw0rk1n]

Thank you, Sutremaine and Ian.

I just checked the map again and realized that the window is actually facing North-West. The plants get some sun in the afternoon, but not enough...

I was hoping to install the lights at the ceiling, so that I don't block the sun, but I did not realize that I will be losing a lot of artificial light. The light would be around 3.5 feet from the plants. At that height, would T5 HO be a waste and LED would be still a valid option?

If I go with LEDs at the ceiling, do I need 1000W (~9000 lumens) for 4.5 sq ft? (They are expensive: $1 / Watt)

[iann]

Mounting any light three or four feet away from a small area of plants is a challenge. Getting all the light onto the plants is difficult, especially since you won't want to be blocking either the window side, or presumably the indoor side, completely to reflect all the light down.

1000W is excessive. I know people who would hang a 1000W light on the ceiling and grow plants under it, but they're wasting 90% of the light and could do the same job with 100W and a bit more care. Plus your room would be ridiculously hot and you'd quickly be ridiculously broke. LEDs are more directional than fluorescents, and you might be able to do something useful with 100W or so. You'd have to look at the spec for the lights, although very few people selling them as plant lights will be able to give you reliable info. $1/W is excessive, maybe twice what you need to pay. That is the sort of rip-off I was talking about from so many LED plant light sellers. They aim to convince you they're selling some "special" product which deserves a higher price when they're just importing dirt-cheap LEDs from China.

[CactusFanDan]

I have a similar window to you, which I've been using for a while with some success. I have two 4 foot fluorescent tubes suspended over the plants that I keep there. The light is about 1 foot away from the plants and I also get some sun in the late afternoon, but none over winter. My plants still look alright.

[dw0rk1n]

Thank you, CactusFanDan.

After searching for decent LEDs, I could not find anything reasonably priced

Going back to fluorescent, this is the best I could find:

http://www.thelashop.com/4-t5-ho-fluore ... 6400k.html" onclick="window.open(this.href);return false;
http://www.thelashop.com/4-t5-ho-fluore ... 6400k.html" onclick="window.open(this.href);return false;

4 ft tubes, 2x54W or 4x54W, 3.5 ft away from the 4.5 sq ft area. They have an option to mix 6400K+3000K or 2x6400K.

Unless you guys think it's a waste, I am going to try this.

[iann]

Four seems like overkill for that space, but always nice to have the option of more light. Having 2+2 with separate switches would be good.

Here's a little thing to consider when buying fluorescents. Can you see the tube from the side? Then where is the light going? Straight out the window. Just for fun, have you considered mounting the lights closer to the plants, but inside rather than above? The outside is probably getting enough light anyway from the sun, certainly more than you lights will provide, but the side of the plants facing in will be getting effectively nothing.

BTW, anyone who says their reflectors have 95% reflectance is probably lying. Aluminium itself reflects slightly over 90% for most visual wavelengths (less in the far red) and will slowly tarnish to well below 90% (cleaning won't prevent this). It is possible to coat aluminium with dielectric layers of precise thickness to achieve reflectances above 95%, but this is not a practical or affordable option for this type of reflector. I don't trust any seller that has to lie to me to sell their product.

[dw0rk1n]

Following your advice, I ended up with 2x54W 4 ft. T5HO. I also lowered it closer to the cacti, without blocking the sun.

IMG00100-20130506-1518a.jpg (87.99 KiB) Viewed 2134 times

How would I choose which cacti should be under the light? Should I be concerned that they may not be used to 16 hours of "sun"?

Some cacti, such as Gymnocalyciums like some shade. Should I keep them on a different windowsill?

Thanks!

[iann]

You're not going to scorch any of your cacti with the lights. Maybe with the sun if it comes through the window strong enough, but never with fluorescent lights. If the fluorescent light level is too high for any plant, it will get stressed over a period of time, may redden and stop growing, but you should have lots of time to move it away.

[dw0rk1n]

Thanks, again.

I added a timer to my setup. How many hours, at what time, should I keep the lights on? Currently, the sunrise in my area is at 5:45 a.m. and sunset is at 8 p.m.

[Saxicola]

Any chance of putting them outside for the summer? You are doing the best you can with your indoor situation, but you have about 4 months or so now where your temps would be good for them. Even a shady spot outdoors is likely to provide more light than indoors with lights. Several good outdoor growing months would do them a lot of good. Just make sure if they go in full sun you acclimate them first.

[dw0rk1n]

I am afraid of too much rain, possibly wind, and also insects. I might experiment with a few plants.

Still looking for advice on how many hours to run the artificial light? Should I match sunrise and sunset? Or it does not hurt to add a few ours before and after?

[CactusFanDan]

I run mine from 7am to 9pm year-round. A 14 hour photoperiod seems to do them well. I think I only used 14 hours, since I was familiar with reptiles and a 14 hour photoperiod is recommended for a lot of reptiles. Cacti aren't reptiles, so you can give them more hours of light if you want. My seedlings get 18 hours of light a day and they're very happy.