MH and HPS light

I’m thinking that I need to buy a second 600w HPS bulb when I switch to 12/12 for my flowering, or do I ?
Already have a MH for veg and a HPS for flower, both 600w. Do I need to buy another HPS bulb or can I run both MH and HPS together. My tent is 8x4x6 with 5 plants that are really close to flipping. I have one monster clone that’s close to harvest. When that’s done I will take the partition down, open my tent back up to it’s full size and put my plants right down the centre, thoughts anyone
Edit: Just had a thought, with a tent that size am I right in thinking I will probably need a third light?

My understanding is that you can run MH through the whole cycle but, it is also my understanding that, switching to HPS, will give you better flower and denser, better buds. Something about the red light spectrum in the HPS, I believe. I’m confused, maybe it’s the damn dope, are you saying that you have 2 600w fixtures, or one fixture and 2 bulbs? I have a 1000w air cooled HID fixture. I have a 1000w MH bulb and 1000w HPS bulb. My intent was to run MH until ready to flower, then remove the MH bulb and put the HPS bulb in for flower. Unfortunately/FORTUNATELY, I am no longer using this fixture at the moment. I’m now running the HLG LED lights and my plants seem to be loving it. Personally, if I was considering purchasing another fixture, It would be an LED from HLG, Well worth the extra cash. I am currently running 3 in my 5x5. I hope that this helps :v:

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@repins12 I have 2 fixtures. One has a 600w MH and one has a 600w HPS. I was going to remove the MH bulb and put another 600w HPS in as my ballast supports both MH and HPS. So you have 3 lights in your tent, I think I will need the same. I will have a look at Leds and see what’s there

If you have 2 fixtures and are going to stay with the HID set-up that you have, I would buy another MH and another HPS bulb. I would then run the 2 MH bulbs in the fixtures during veg and the 2 HPS bulbs during flower. This is just based on what I have learned and what I understand, like I said I am new to this indoor growing thing as well. My first auto, I ran the MH the entire life cycle and the smoke is respectable. Gets me all effed up at least. If I was considering the LED route, personally, I would definitely go the HLG route. I hope this helps :v:

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I think the second HPS is my first option but I’m also looking at led as well now. I can’t invest in led just now but probably will do later on. Thanks for your advice and enjoy the smoke :sunglasses:

@Davyg, if you would like, I will tag you in on my post and you can take a look, if you want :v:

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I run 4 in a 4x8 and 3 in a 4x6

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Easiest way to factor in lights needed is watts/ sq ft

I try to get around 45+


@repins12 that would be great if you could tag e in your post, thank you
@PharmerBob is that 4 led panels you have?
I think I need 1600w in my 8x4x6 tent

1600 would put you right in the money

Yes I push 4 260 an and 2 burples for far red spec.

Haven’t upgraded to hlg rspec yet


The hlg respec are the ones that I just purchased and my plants are loving them, hopefully they will be showing me some love soon :+1:


A 600 watt hps can grow up to a pound or more in a 4x4 area and a 600 watt CMH is not far behind and will provide a larger color spectrum combined with the HPS.
Another 600 watt hps will definitely yield you more but you will pay more in electricity and fight a considerable amount of heat.

I don’t know what kind if yield your looking for but I personally think two pounds is pretty attainable with the setup you have now.

If you don’t mind paying higher prices for lights and cooling and want more than two pounds then get that third light but you will have to step up your “grow game” with that third light.

I honestly would consider small wattage LEDs as the “salt and pepper” to go along with your “meat and potatoes”. A couple 100 watt quality quantum boards will go a long way in your setup. What you think @dbrn32?


That’s 1600 watts of pure heat if your thinking about another hps.

You need to start thinking in micromoles per second

Quantum boards produce roughly 2.5 times as much light per watt than an HPS does.

So a 100 watt quantum board will produce about the same amount of light as a 250watt HPS… two 100 watt QBs wil give you about the equivalent of 500watts of HPS power but even more efficient because of less heat and a larger foot print because you can spread them apart


I’m properly skint just now as I’ve spent a small fortune on my kit so far. I will however look at the quantum boards when my finances are up a bit. Good shout on running both lights to get a wider spectrum of light, as for the heat I didn’t allow for that. I will upgrade as soon as is practical because my electric bill is a bit on the scary side :scream::scream::scream:. As for yield, I’m quite happy with what I have I just need to get my shit in order. I had no idea what to expect with regards to yield but from last harvest I’m sure it was around 2lb dry. My 5 blueberry are doing well and I just want so much to get this one properly dialed in. @Myfriendis410 told me that my garden would become “very zen like” and he was spot on. I love just sitting there in the peace and quiet just watching nature go about her business. My plants tell me when they’re hungry or cold or whatever. Maybe I’m just an old hippy imagining things but personally I love it


It seems like we did get a little off subject. I think the answer to you original question is yes, you can and probably should, if you want to try something different, get another HPS bulb and run both HPS during flower. Especially if you don’t want to spend a bunch of cash right now. I think we got off center when, I was unsure whether you already had 2 fixtures or were going to purchase another. If I didn’t want to put a bunch of cash out right now, I would get another HPS bulb and run the 2 HPS bulbs during flower and get another MH bulb and run the 2 MH bulbs during veg on your next grow. That would be the simplest solution to what you are trying to accomplish for the time being :v:



Here is a little some thing that should help you out.

Metal Halide - MH

Metal halide bulbs produce an abundance of light in the blue spectrum. This color of light promotes
cannabis plant growth and is excellent for green leafy growth and keeping cannabis plants compact.
It is the best type of light to be used as a primary light source (if no or little natural sunlight
is available). The average lifespan is about 10,000 cumulative hours. The bulb will light up beyond
this time but due to the gradual decline of light, it is not worth your while to wait for the bulb to
finally burn out. If you compare their lumen (brightness) per unit of energy consumed, metal halides
produce up to 125 lumens per watt compared to 39 lumens per watt with fluorescent lights and 18 lumens
per watt for standard incandescent bulbs.

High Pressure Sodium - HPS

High pressure sodium bulbs emit an orange-red glow. This band of light triggers hormones in
cannabis plants to increase flowering/budding in cannabis plants. They are the best lights
available for secondary or supplemental lighting (used in conjunction with natural sunlight).
This is ideal for greenhouse growing applications.

Not only is this a great flowering light, it has two features that make it a more economical
choice. Their average lifespan is twice that of metal halides, but after 18,000 hours of use,
they will start to draw more electricity than their rated watts while gradually producing less
light. HPS bulbs are very efficient. They produce up to 140 lumens per watt. Their disadvantage
is they are deficient in the blue spectrum.

If a gardener were to start a young cannabis plant under a HPS bulb, she/he would see impressive
vertical growth. In fact, probably too impressive. Most cannabis plants would grow up thin and lanky and in no time you will have to prune your cannabis plant back before it grows into the light fixture. The exception to this is using a HPS light in a greenhouse. Sunlight is high in the blue spectrum which would offset any stretching caused by HPS bulbs.

Common manufacturers of metal halide and high pressure (HP) sodium lights include Philips,
General Electric, Iwasaki, Venture, and Osram/Sylvania. Many of the manufacturers buy and use
the same components, often manufactured by competitors. Most often the bulbs have the exact same
technical statistics.

Lighting Chart - A guide for wattage per square foot.
HID Light Output Primary Growing Area Supplemental Area
100 watts 2’ x 2’ 3’ x 3’
250 watts 3’ x 3’ 4’ x 4’
400 watts 4’ x 4’ 6’ x 6’
600 watts 6’ x 6’ 8’ x 8’
1000 watts 8’ x 8’ 12’ x 12’


You want to keep the mh bulb in until the flower stretch is about over then put your hps in. Then the last week, week and a half of flowering put my bulb back in. Helps tricomes


I like the info given until you get to bottom. There is no way anyone could produce anything besides larf trying to flower a 8x8 with 1x 600w hps/mh light


@repins12 we got off topic a little but it’s nice to go for a ramble sometimes :sunglasses:
@garrigan62 that info with all the light and plant data on it is excellent, its getting downloaded and stored. Thank you for that
@HornHead I used one 600w HPS for my last grow. I had 4 plants underneath my air cooled hood and it worked well enough. I have my big tent now and need to expand both my lighting and by the sounds of it my cooling as well. Do I put the MH back in just before harvest?


Yes, in theory the far blue spectrum I believe it is, helps tricomes production in the last week or two @dbrn32 can explain better than I