View Full Version : Do I need both MH and HPS bulbs?

05-22-2006, 05:32 PM
Do I need both MH and HPS bulbs? Can I use just one of these bulbs?

overgrow the world
05-23-2006, 01:04 PM
use a mh for veging because it has more of a blue spectrum. then hps for budding because it has more red. you can use a hps the whole time but if you want the best quality crop veg with m.h. then flower with hps. digital ballasts are cool because you can run both types of light on the same ballast

05-23-2006, 08:53 PM
I dont think you need both HPS and MH any more. You can get a enhanced/conversion bulb for either. They work great :)

05-24-2006, 12:20 PM
Using an MH bulb in the veg is going to give you tighter internode spacing and a faster growth rate.

the Dirty Dragon
06-02-2006, 12:06 PM
I dont think you need both HPS and MH any more.

Exactly, buying an MH is a waste of money.

The extended spectrum HPS's are better, produce a wider spectrum, more lumens, and don't require a seperate ballast.

06-02-2006, 12:55 PM
You can veg with an HPS. You can also bloom with an MH. Neither of those are ideal. Sure if you can only afford one ballast then HPS is the way to go. But if you are doing any kind of production...anyone will tell you that MH is absolutely necessary in the veg. If you veg with an HPS you will get stretching. That will result in spindly low yielding plants. MH and HPS are designed to replicate the spectrum of the sun in different seasons. MH is supposed to represent the type of light that plants would get in the spring ( when most plants are beginning to sprout). HPS replicates the sun spectrum during the summer months (when most plants are in bloom). You might try vegging under an MH...you'll see a world of difference.;)

07-12-2006, 02:52 AM
Despite all the completely misleading statements regarding how you 'don't need MH because you can use a HPS with a wider spectrum" (the HPS bulb by Agrosun (made for Hydrofarm by Sylvania, as are all "Agro" bulbs) the reality is - as always, a question of investment vs. return. To state that, "You do not need a MH," is *true* but leaves out the FACT that a MH is a *vastly* superior bulb for vegetative growth. Even if you get a HPS and use a conversion bulb (which is what I do, I have one 400w MH, one 400w HPS, and run the standard bulbs in the one I am primarily using (MH system has a 400w MH bulb during vegetative period while the HPS has a conversion bulb immitating MH spectrum to maximize the spectrum used by the plant during this period of its liffe cycle, when I switch to 12/12 and flowering, I swap the MH bulb out for the MH to HPS conversion, and remove the HPS to MH conversion from the HPS system and replace it with a 430w SunAgro HPS bulb, best of both worlds for a reasonable price).
So instead of buying one MH and one HPS you can get one of either and use a conversion bulb to compensate for the color spectrum difference produced by the different types of bulbs. If you doubt there is a difference, try this simple test. Go to a grow store and look at the color of a MH light from a few feet away, dont stare at it, just look. Then go to a HPS and look. Hmmm. MH = blue, HPS = red. Yes, there *is* a difference. And NO this has NOT gone away with the newer Red bulbs and Hortilux Blues etc.

While the posters are technically correct, they violate the spirit of the question, I believe. I felt you wanted to know not if you *NEED* as in "if I dont have this will my plants die?" but "will I see noticable results if I use the different bulbs for the purpose they best fulfill?" and the answer to that is YES you will see that vegetative growth is stronger and plants less leggy with a MH in vege and the HPS will increase flowering BUT your plants will stretch, your leaves will begin to yellow, etc because despite improvements, the reality is the spectrum or color temperature of the lights are different enough to cause physical changes in the plants.

Supporting statement, nothing radical, from a good little site specializing in bulbs, tiny but educated place, they address this issue in their FAQ:

"Frequently Asked Questions (and answers).

Q. What is the difference between Metal Halide and High Pressure Sodium?
A. The spectrum and comparative lumen output (brightness) per watt. If you had to choose just one or the other, the Metal Halide provides the better all-purpose spectrum for plant growth. It is strong in blue and indigo which promotes compact stem and leaf production. It is a better light for the early stages of growth, when leaf and stem production are most important. In the flowering stage, there is just enough red and yellow to produce average flowering.
The High Pressure Sodium comes into its own as a flowering light. It is strong in the red/yellow part of the spectrum which promotes larger and more abundant blooms with longer stems. It is more efficient and brighter (lumens per watt), than the Metal Halide, which increases yield.

Q. Would a warm Metal Halide be as good for flowering as a HPS?
A. In our opinion, no. Which is why the combi lights and switchable ballasts are such a good idea."

I hope this helped.
Gooster the growster

11-03-2010, 05:15 PM
Hi gooster, your post has been quite informative :).

I came across this post with a very specific question in mind, and you came very close to answering it.

I aquired a few things, and wanted to put them to use to the best of their ability. I am lighting a single, 3x3 grow space with approximately 15 plants in it. Cycle I am trying is: 1 week of Veg, then immediately into the flowering stage. I have a single, 'dual bulbed hood' (hood with 2 sockets), being powered by a dual 400W ballast (one 400 HPS, and one 400 MH). During week 1, only the MH was on at 18/6 cycle. week 2, I dropped the Daylight hours by 1 every day until I hit 12/12. sometime during week 2, I switched the HPS light on.

now about at week 6, flowers are doing great... I am wondering if there is any benefit/consequence or if there is any experience on having BOTH lights on?? Does the doubling of lumens, and increased wavelength range outweigh the benefits of having a the light in the solid red spectrum at a mere 400W?

Basically, which is better during late flowering:
400W HPS only
400w HPS + 400W MH together


01-11-2011, 11:51 PM
It really all depends on if you want to change colors and how much crop you are trying to produce and all that. HPS are the more diverse of the two, but they both have their place in the growing process.

01-28-2011, 06:26 AM
It depends upon color choice.If you want blue light then you have to use MH bulb and if you want red light then you have to use HPS.

01-29-2011, 02:42 PM
You can get a enhanced/conversion bulb for either. They work great :)

+ 1, its a great idea, gives you equal amounts of both spectrum's of blue and red, or atleast to my knowledge.

03-18-2011, 09:23 AM
If I were you I will go with LED High Bay Lights. It could say lots of energy. I'm selling high bays from China. I have high bay up to 200W.

11-25-2011, 11:57 AM
can you add an incandescent bulb either red or blue to add the lacking color.

12-07-2011, 04:59 PM

Can a person consider all t5 ho 4 bulb 4ft flourescent lighting with a bulb of 6500k vs. MH. What would i notice if i added a 250w mh to the mix?