Can't find an 800 HPS bulb-will 1000 be ok?

My tent is 5x5. I’ll only have 3-5 plants at a time in there. I have 3 (10 gallon) pots with coco ready to move in as soon as the seedlings are ready. My light is not dimmable so should I use a 1000 HPS or something smaller? Thanks for all the help!

What’s the ballast rated for. And I would recommend getting a digital dimmable one

Oh brother I don’t even know what ballast means—I have not purchased it yet so I’ll get anything you recommend. A digital dimmable one? Sorry that’s greek to me too.

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A 1000 watt HID light will be perfect for your 5x5 tent.

A ballast is essentially the thing that supplies power to your light.
A digital dimmable ballast can be handy if you want to reduce the power, like if you need to reduce the temperature a bit, want the light closer to the plants or have just moved plants into the tent that are just beginning to flower. Or, in your particular case - seedlings. With a dimmable ballast, you can drop that 1000 watt bulb down to 500 watts.
The bulb should match the ballast. So, if it’s a 1000 watt ballast, you should have a 1000 watt bulb.

Note: You will actually want to use an MH (Metal Halide) bulb during the vegetative stage and switch to HPS (High Pressure Sodium) during the flowering stage. You can use either bulb for the entire growth process, but MH is better for vegetative and HPS is better for flowering.

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Like I suggested in the other thread, 2 separate 400w lamps would give you more options and perhaps better coverage over the canopy.

Can you post the make and model of the 400w you already own?

Sun System
Yield Master 4” reflector

1000 watt max

I just ordered (4) 400 bulbs. Adding another light a friend is giving me and I’ll have (2) 400’s going when needed. Whew. I think I got it. Thanks a million.

Can I also ask when do you leave the sides of the tent open where there is ventilation? Are they to be closed just during flowering?


Real quick, did you buy 2 extra bulbs as spares?

As far as ventilation, and tents, you want to invest in an inline fan with flexible ducting. I strongly recommend a quality carbon filter to reduce the smell. Can you link to your specific tent on amazon so we can strategize how to vent it best?

One tip, before you get too far along, set your empty tent up and sit in it all sealed up. Leave the room lights on, but make sure the tent is absolutely dark and fully sealed. Listen to music or something for 20m, but no screens. The idea is to see if there are light leaks in your new tent. They’re usually easy to address once you find them, but you have to find them.

Personally, I feel you would be better with a 1000 over two 400’s. Mainly because the efficacy on 400’s is horrible in comparison to bigger hid lights. If you already have them though, it does offer a little more flexibility in coverage having multiple fixtures.


I defer to dbrn on this. The multiple lower watt fixture advice comes from Jorge Cervantes, but it’s anecdotal, dated, and recommends 2-600watt lights over a single 1000w.

The only advantage is that the OP can add the lights to the tent in smaller increments, which could save on electricity, thus offsetting the loss in efficacy (potentially).

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I’ve had my tent set up for months now, trying to grow some monster clones (3 out of 14 made it). The light is totally blocked out. I have an exhaust fan, a humidifier with an oscillating fan, an oil filled heater and a mister in the tent, along with one light—adding another today. Will have one 400 hps watt bulb in each light. My seeds are sprouting, so I’ll have 3 -10 gal. pots and 3 small clones growing in the tent. The ventilation panels on the side of the tent have been closed, just not sure when if ever they should be open. And is 20/4 good for the lighting once the seeds have sprouted? I could go on with thousands of questions…but I will try to not do that. Thanks so much!

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Two 600’s over 1000 is different story. the 600’s are most efficient of the three. Then 1000, then a significant drop to the 400’s. It’s a big enough difference that two 400’s is similar amount of light to 1 600.


20/4 is fine. Anything between 16/8 and 20/4 is reasonable, IMHO. The dark period is probably very important for vegetative growth, so a longer light period might be counterproductive; jury is still out in that. You can save a little money on electricity if you want by going 16/8.

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Learned something new!

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@Dealra not to throw too much at you, but there’s another option which might be an even better fit. Wait for others to chime in on how this would work, the risks, and how you’d transition to flower.

You can run 6/2, cycling thru that 3x per day. The advantage there is you have more flexibility to get in and attend to the plants.

I suppose the flowering equivalent would be 4/4, 3x per day.

Have you already purchased a light? Strike that I see later that you have. In the future, should you care to upgrade, there are some pretty sweet LED options now! You save on energy, less heat to deal with too. Personally, from a safety standpoint alone they are superior. No exploding bulbs! Not that it happens much but dont spray water on HPS or MH bulbs! Dont touch them unless you want to leave your skin there! Do not get your hair on one! Led is also less of a fire hazard. Ultimately you get far longer lamp life too. So in the future it would be a good idea to investigate LED as your next light investment. Not a cheapo blurple though lol.

-I will go the led route when I need to…Most everything was given to me by an old long time grower that retired from it. His stuff is ancient but I have solar electric so I am hoping it will not be too costly. I do look forward to upgrading though.

Would you know when the side vents of the tent need to be opened, if at all?

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Well, no matter which lighting system you use, good ventilation is required pretty much all the time. Plants transpire and need to exchange air constantly. I suggest you get a thermometer and a way to read the humidity in your grow space. They are pretty cheap and can found on Amazon or any grow store. That said, some controllers such as the Inkbird ( cheap and pretty good ) have a sensor that reads humidity and temperature. You set it to turn you fan on to ventilate when temos are too high or humidity is too high. You will most likely want a carbon filter lest ye be wanting Pepe Lepeu in your house. There are some pretty good grow tent setup videos online that can take you through the basics. If the hood your friend gave you is a sealed hood with a vent pass through thats great! You can vent your tent through the light fixture to keep things cooler.

You need to have air exchange in your tent. As such, you should have one vent on the bottom open all the time, and your exhaust fan exiting at the top on the opposite site. You can use a bit of flexible ducting in an “S” or “U” shape so that light can’t enter the tent. I like to cut off the “foot” of a piece of pantyhose and put it over the inlet ducting to act as a filter as well.