Question re: HID bulb choices for my application

TT, zone 5b MAJuly 27, 2008

Hi -

This fall, I will need to replace 1000W, 600W, and 400W HID bulbs for subtropical/tropical bonsai and some South African and Madagascan succulents. In general terms, my needs are to extend the growing season somewhat (in a sunroom with skylights) - then to ease most of them into a light dormancy (aka limp along period), trying to give them as much light as possible during the dark Massachusetts winter. During this period, most of bonsai growth will slow to a crawl and the succulents will enter a dry dormancy (except for those that are winter-growing species).

The bulbs I will be replacing are:

1) 1000W Sunmaster Cool Deluxe metal halide

2) 600W Sunmaster Cool Deluxe MH Conversion Bulb

3) 400W Eye Hortilux Super Metal Halide

To switch it up a bit (and, based on HTG prices, to save a few bucks), I was considering the following:

1) AgroMax 1,000 watt Metal Halide 6500K Ultra Blue Daylight Spectrum Bulb

2) GrowBright 600 Watt MH Conversion Bulb

3) AgroMax 400 watt Metal Halide - 6500K Ultra Blue Daylight Spectrum Bulb

Bad ideas? Anyone have any experience with any of these?

Thanks in advance for any input.


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Buy a 600W High Pressure Sodium Ballast Kit from HTG for $105, and rewire your 600W Metal Halide ballast so it will run HPS instead. Then buy the 600W reflectorized HPS lamp from HTG for $60. For $165, you will now have the combined spectrum of metal halide and HPS, plus you will have an absolute killer of an HPS lamp, that will probably outperform your 600W MH conversion lamp two to one. Remember, HPS lumens are more effective as PLANT LUMENS than a metal halide, plus you get more photons per watt. By doing this, you won't even need to run your 400W metal Halide, thereby saving you the cost of the AgroMax, and saving you the cost of the electricity. That's what I would do :) Sativa.

    Bookmark   July 28, 2008 at 6:57PM
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for your 600W, that means you already have a 600W HPS ballast, so that will save you the cost of getting one, of course. Just use the $60 HPS lamp I mentioned, it's an absolute beauty of engineering, will outperform the conversion lamp 2 to 1, and during your really slow periods of growth, that lamp may be sufficient on its own. :) Sativa.

    Bookmark   July 28, 2008 at 7:11PM
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TT, zone 5b MA

So, let me get this straigtht - I already have a 600W HPS Ballast (I have been running the MH Conversion bulb on it). If I buy the 600W reflectorized HPS lamp that you suggest, I can run it off that same ballast? What do I insert the lamp into - my Sun System hood? Or, do I need something else?

The 400W MH is running over a different set of growing stands, over different plants. Do you think that the reflectorized HPS lamp will cover more square footage than a conversion bulb?

BTW, any opinion on the Agromax lamps?



    Bookmark   July 28, 2008 at 8:19PM
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Usually the reflectorized lamp just uses a simple L shaped bracket. the short part of the L has the octagon box with the mogul socket, and the long part of the L has 2 little hooks on it so that you can hang it from the ceiling using little chains. I'm sure HTG supply can supply the right item, and it should be pretty inexpensive compared to a hood. The reflectorized HPS will certainly cover more square footage than the conversion lamp -
for 2 reasons, 1 - the reflector is much better than the sun system hood, and 2 - probably close to twice the number of plant lumens from this lamp, compared to the MH conversion.
You should be able to cover twice the square footage with an equal amount of light.

While you're at it, since you already have the 600w HPS ballast, buy the 400w HPS ballast kit from HTG for about $50, rewire your 400W MH ballast box, and then buy a PHILLIPS CMH Ceramic Metal Halide lamp. this will be much better than your Agromax lamp. HTG does not sell the Ceramic Metal Halide, but you can get it online for inbetween 48$ and $53. Since this is a commercial lamp, it does not have the "agricultural" premium put on the price, and everyone who uses it finds that it is absolutely the best. There are threads on this forum, where people talk about the CMH lamp, and also a nice long thread on Potgrowers are very difficult to fool, and they tend not to fall for b.*. and hype, they are by nature sceptical, and the conclusion on is that people who use the CMH lamp for their vegetative phase growth love it, it works much better than HPS or Metal Halide for vegetative growth, it runs off a regular HPS ballast, and then once their cannabis is in a well established flowering phase, then they switch to HPS, in order to get the best yield, potency, etc. Also, the CMH lamp lasts longer than a metal halide, has better maintained lumens, so in the long run you will save money, besides having a nicer grow result. :) Sativa.

Here is a link that might be useful: Link to reflectorized lamp performance, notice strong radiation in 550-620 nm wavelength, excellent for photosynthesis, and exceptional reflective pattern.

    Bookmark   July 29, 2008 at 3:19AM
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CMH has extraordinary color rendition index, meaning your plants will look very pretty, just like under natural sunlight, because the output of the CMH lamp is almost just like the sun, straight and continuous right across the spectrum. The very fine representation in the longer wavelengths really matches the plant photosynthesis action spectrum region of maximum efficiency - meaning that longer wavelengths are twice as effective as shorter wavelengths for photosynthesis, and the CMH lamp is very rich in these areas, compared to the metal halide you describe. Sativa.

Here is a link that might be useful: Very fine reference on how to convert a given spectal output into plant lumens.

    Bookmark   July 29, 2008 at 3:34AM
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TT, zone 5b MA

Thanks for all this information - much appreciated!

You wrote "buy the 400w HPS ballast kit from HTG for about $50, rewire your 400W MH ballast box, and then buy a PHILLIPS CMH Ceramic Metal Halide lamp. this will be much better than your Agromax lamp." Why do I need to convert a MH ballast to run the Phillips CMH Metal Halide lamp?

I was looking at those lamps, and was disappointed to see that they do not make them in larger sizes, too (e.g., 1000W). I still need to get a 1000W lamp, as well...

Thanks again.


    Bookmark   July 29, 2008 at 6:33AM
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TT, zone 5b MA

Oh, one other clarifying question - If I opt to go with the reflectorized 600W HPS bulb that you recommended, can I run it in my current Sunmaster hood safely, or do I need to switch out my hood for the L shaped bracket you describe?



    Bookmark   July 29, 2008 at 6:59AM
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Even though it's called Ceramic Metal Halide, they started with an HPS lamp, and spiked it with some rare earth metals, or something like that, so the 400w lamp runs on an HPS ballast (I know, confusing). Some of the smaller wattages are designed for an MH ballast, but the 400 needs an HPS. Unfortunately only up to 400w is currently available, but I've heard they're working on larger lamps.

And there is no problem running the reflectorized lamp in the Sunmaster hood. Cheers, Sativa.

    Bookmark   July 29, 2008 at 8:58AM
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TT, zone 5b MA

Sativa -

So, to convert my 400W MH ballast to a 400W HPS ballast (so that it will run the CMH lamp) what do I need to purchase? Are these conversion kits universal to any type of MH ballast that you want to convert (e.g., I believe mine is a Sunsystem, but I would have to check)?



    Bookmark   July 29, 2008 at 11:04AM
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Hi, to make an MH ballast into an HPS ballast, you buy the ballast kit from HTG supply for $55. This is a universal conversion kit. It includes a transformer, capacitor, ignitor, brackets and screws, probably some wire, connectors, a mogul socket, and full set of instructions.

You will remove several parts of your existing ballast: you will need to open the case, remove the innards, and substitute them with the new ones. You will keep the case, the plug and cord that you use to plug the ballast into the wall, and the cord that runs from the ballast to your octagon box with mogul socket. All the rest is replaced, so you are left over with an MH transformer and a few other goodies, that you will no longer use, because they have become obsolete. HTG claims they include PROPER INSTRUCTIONS, so I believe them. Now enjoy the beauty of CMH, you and your plants will love it. For 55$ for the kit, and $50 for the lamp, you have a winner that will beat the pants off the AgroMax, AND you will be able to run a reflectorized 400w HPS lamp to boot, should you so choose.

You will also be using a 1000W agromax MH lamp, which is a real monster of a workhorse and a beauty of a lamp, for only $70, that's a bargain. I wouldn't change that part at all.
It will be generating heat of course, but hopefully your greenhouse is attached to your house, so the heat from the lamp will both keep your greenhouse a pleasant temperature, and also moderate you house heating cost somewhat.
Total lumens = 95,000 + 95,000 + 32,000 = 222,000 lumens
This is a serious amount of light. What is the square footage of the garden anyway - this amount of light would be good for 90 square feet of vegetative phase growth, and 30+ square feet of cannabis in the flowering phase.
Nice. :) Sativa.

    Bookmark   July 29, 2008 at 6:38PM
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TT, zone 5b MA


Calculating the area that I am covering has always been tricky to me. Basically, I have three bench areas in a 13x13 sunroom. There are also large windows and three skylights, but the room faces north - so in the dead of winter there is not much useful outdoor light coming in. Some of my stuff goes dormant to semi-dormant (which is okay), some of my stuff I force into dormancy with drought (Madagascan succulents) which they are supposed to do.

My concern is always that there is enough light there when it needs to be, i.e., when stuff is awake or waking up. Most of these plants love high intensity light.

The bench areas (each bench is three tiers) are:

1) approximately 8'x3' under the 400W fixture.
2) approximately 8'x4' under the 600W fixture.
3) approx. 7'x6' under the 1000W fixture.

So, what is that - about 92 square feet?

I always feel like I am shortchanging the plants on the ends of the benches, and try my best to get the most light-loving ones in the center.

Obviously, the plants on the bottom shelf of each bench gets the weakest light. The 400W is about 12 inches from the closest plant tops, the 600W is about 24 inches, and the 1000W is about 28 inches or so from the nearest plant. I have not burned a plant ever at these distances... In the brightest spots, I measure 6-7000 footcandles usually. In the weaker spots, anywhere from 3-5000 footcandles (in the lighted areas, of course). I run the lights for about 11 hours a day in the winter.

I am positive that I could be better arranging my growing area to take advantage of these lights, but I do the best I can. If you are ever in the area, let me know - I could use the objective opinion...;-).

Wonder if I will need to adjust my distances with these new bulbs?


    Bookmark   July 29, 2008 at 9:15PM
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The best way to see if the lights are too close is to place your palm on top of the tallest plant. If the back of your hand seems too hot, or is burning hot, your plant will feel likewise.


    Bookmark   July 29, 2008 at 10:13PM
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TT, zone 5b MA

Hi Zink -

Yes, I have tried that test and determined that the height seemed good to me. I don't think I am any more heat tolerant than a Baobab (hopefully!).


    Bookmark   July 30, 2008 at 6:28AM
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TT, zone 5b MA

Hi -

Just wanted to say thanks (especially to cannabisgrower) for all the help with my choices. Just to close this out (for anyone interested), here is what I went with:

1) I bailed on my 600W HPS to MH conversion lamp and went with the Reflectorized HPS lamp,
2) I moved from the Sunmaster 1000W Cool Deluxe MH to the AgroMax 1,000 watt Metal Halide 6500K Ultra Blue Daylight Spectrum Bulb (thought I would switch it up...),
3) I went from a standard Eye Hortilux 400W MH to the AgroMax 400 watt Metal Halide - 6500K Ultra Blue Daylight Spectrum Bulb.

I thought long and hard about cannabisgrower's recommendation to convert my 400W MH ballast to an HPS ballast and get to the CMH bulb, but I didn't trust my electrical skills. Cost was also a consideration.

Thanks again for the help! Can't wait for winter now!


    Bookmark   July 30, 2008 at 4:04PM
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I agree that CMH provides the best combination of spectrum
and output. However this bulb runs either on the GE Ultramax
digital ballast, or a magnetic 400w HPS ballast.

The halide and HPS ballasts use different transformers for a
reason, because each transformer is tailored to the bulb.
You can change the capacitor and add or subtract an ignitor,
and Jerry-rig one into the other, but then you have less than optimum performance.

The HPS ballast doesn't cost that much more, if any, than
a MH ballast plus retro-kit. The bulb determines the
spectrum, it's not like you can start with a MH ballast,
convert to a sub-optimal HPS ballast, and then get some
kind of MH spectrum boost.

Generally I would stay away from 1000w lights, because of
the high concentration of light and heat. It's better to
have more points of smaller wattage lights, for more even
distribution of light (and better bulb selection).

For the 600w ballast you now have, you didn't say whether
this was digital or magnetic. For this ballast, I recommend
the PSMH (pulse-start metal halide) because it comes in
choice of spectrums and is more efficient than the retro
bulb you mention.

    Bookmark   August 6, 2008 at 4:20PM
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