Hello every cactus lover: I need help. Thanks.(Grow light)

euphonium · Post by **euphonium** » Sun Sep 24, 2006 11:02 pm

Hi every cactus master,

I am from Taiwan. Recently I found this interesting website when I was surfing on line. A lot of enthusiasts share their own invaluable experiences with other beginners.

I have a question about the growlight. I plan to set up a grow light system for my cacti since I will relocate to New England. In the winter of Boston, I may place them in several big acrylic storage boxes to make sure that the snow and frost will not kill my precious.

If somebody can give me suggestions about HPS (High pressure sodium) light and MH (Metal Halide) light system, I would appreciate it very much!!

Hopefully my poor Arios can live happily with me in the future.

Jonathan

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Post by **daiv** » Mon Sep 25, 2006 5:03 am

Welcome Jonathan!

I don't have any experience with those types of lights, but use flourescent lights with my Orchids and have no trouble with them.

Just remember, artificial light is not nearly as intense as sunlight. You can help make up for this with time. Keeping your lights on for about 18 hours can approximate maybe 6 hours of daylight, but don't leave them on continually. You can also lessen the time on the bulbs if you have some sunlight too.

atsar · Post by **atsar** » Mon Sep 25, 2006 10:57 am

the best kind of light to buy is hps,as the ballast will also run a mh bulb,though i personally have a dual spectrum hps light,which emits both the spectrums of light,metal haldide is a blueish light which emits 6400k spectrum,ideal for vegative growth,hps emits an orangeish light which emits 2700k spectrum,ideal for flowering stages,but like i say,i bought dual spectrum hps,which covers both aspects,but if you don't get dual spectrum,just bear in mind that a high pressure sodium ballast will take a metal haldide bulb,but a metal haldide ballast WONT run a high pressure sodium bulb,and they are expensive running,especially during the 18-6 cycle
hope this helps
stef

DieTer-Xz · Post by **DieTer-Xz** » Mon Sep 25, 2006 11:03 am

I can't add anything valuable, but welcome!

iann · Post by **iann** » Mon Sep 25, 2006 1:23 pm

Most HPS ballasts will not operate most metal halide bulbs, and vice versa. There are so-called "conversion" lamps which give you the flexibility to swap bulbs (requires special bulbs), but that seems like a decision to far at this stage.

First, you need to decide how much light you want, based on the number of plants you want to light and how bright you want them to be. Although to some extent you will be compensating for a lack of light intensity with long continuous steady light, a shorter period of bright light is better for overwintering cacti than a long period of dimmer light. Plan on 20W-40W of light per square foot (200W-400W per square metre) and then start thinking about which lights to use.

You should also decide whether you will be supplementing natural light, or providing all the light yourself, for example in a basement. HPS produce the most light from a given amount of electricity but it not the ideal type of light for overwintering cacti without any natural light. HPS is very good for supplementing natural light. You might find that HPS light produces etiolated growth and encourages flowering, neither of which are a good idea for most cacti in the middle of winter. Metal Halide produces a bluer light which encourages compact growth, but is slightly less efficient than HPS. Both HPS and Metal Halides are less efficient at lower powers, below 400W or so, and then you should look at fluorescents which are available in a range of "colours" to suit your needs. Ask for more details when you have an idea how much light you need and which direction you might want to go.

atsar · Post by **atsar** » Mon Sep 25, 2006 2:21 pm

that's not strictly true ian,true metal haldide ballasts will not run a high pressure sodium lamp,but a high pressure sodium ballast will run a metal haldide bulb,providing it's of the same wattage,if you still don't believe me,try screwing a mh bulb into a hps system,you'll be pleasantly surprised,of course,manufacturers of these lights will not tell you that hps ballast can run mh bulbs,as they want you to buy a seperate ballast for each bulb,more profit heh,i always buy hps ballasts because of their versatility,though as i also pointed out in this thread,you can get dual spectrum sodium lamps which emit the same light as mh and hps at the same time

iann · Post by **iann** » Mon Sep 25, 2006 2:45 pm

At your own risk, atsar. If the ballast or bulb isn't designed for it you are damaging the bulb. A lawyer would probably claim it is also dangerous, although I've not heard of anything nasty happening.

The ignition mechanism for metal halides and HPS is different, in fact a metal halide doesn't require any form of ignition and this is the only difference. The ignition sequence needed for an HPS lamp damages a metal halide bulb. The other way around, the lack of any ignition from a metal halide ballast means an HPS bulb won't even light.

euphonium · Post by **euphonium** » Mon Sep 25, 2006 10:24 pm

Hi,

Thank you Iann, Astar, DieTer-Xz, Daiv. This is a really nice place for discussion!

I have about 20 Ariocarpus fissuratus, one big Pachypodium brevicaule, one big Strombocactus disciformis, one medium Dioscorea mexicana, and several lovely seedlings. In previous three years, I placed my cacti near the window and used one 20W mini-growlight bought from Walmart. Fortunately there is no lanky growth observed. Recently I found the job in Boston. That's why those precious have to move with this poor guy from beautiful Oklahoma.

Once I arrive Boston, I plan to set up artificial light to supply the growth. Probably I need three big transparent plastic boxes to accommodate my plants.
I am thinking that if it is proper to use one 300W HPS plus two 6500K fluorescence light bulbs per box. However, I am worried about that HPS may induce the lanky growth of the cacti because it is deprived of blue light. In addition, I am afraid the high temperature of HPS may burn my plastic boxes if I install the light on the lid of the box!

Again, thanks everybody for the incisive suggestions.

Jonathan

readymade · Post by **readymade** » Tue Sep 26, 2006 7:44 pm

Can't decreased distance between the light source and the plant help to compensate for the reduced light as well?

iann · Post by **iann** » Tue Sep 26, 2006 9:14 pm

Its a very interesting point, readymade. One simple way to get more of the light coming from your bulb/tube onto your plants is to put them closer to the light, but I'd like to explain why that is a very poor approach.

People often state that the intensity of the light decreases with the square of the distance from the light, but this is only actually true for a point source of light radiating equally in all directions. So it is approximately true for a halogen or metal halide bulb, but the light decreases more slowly as you move away from a large source like a fluorescent tube, and much more slowly if you are using a reflector. You can see this by considering the extreme cases of focussed directed light such as a searchlight or a laser, where the light intensity hardly decreases at all as you move away from it.

So, to get intense light we can either get very close to the light or focus all the light directly onto the plants. When you get very close to a light, the bottom of a plant may br two or three times further from the light than the top of the plant, as well as much of the light being blocked. Obviously the bottom of the plant will be getting much less light than the top, not a healthy situation. Being so close can cause heating and scorching problems at the top, directly from the light and because of the lack of ventilation, while the bottom is receiving too little light. Focussed light from a reflector gives you the option to place the plants where they can be ventilated, and to get good light to both the top and bottom of the plant. You can achieve a similar result by placing a very strong light source quite distance from the plant. Such strong light sources can cause large utility bills but one of them, the sun, is free!

Lastly I would like to recommend my preferred lighting method. Completely surround the plants with something white, or shiny if you like but white works perfectly well. You don't need a carefully shaped reflector to focus the light directly on the plant, you just make sure that whatever direction the light goes in, it gets bounced back onto the plant eventually. The plants are more evenly illuminated from all sides with this method. Anyway, I like it and recommend anyone planning a light system to consider it rather than just trying to get everything close to the light. Remember, if you can see lots of light then the plants are missing out