Plant Droops Under HPS but not MH?

I recently switched from a 600 Watt MH to 600 Watt HPS after a week of 12/12.

My light is on during the night. In the morning after the first day of 12/12 the plants had drooped. I don't believe due to water, as it had been at least a day since watering. I thought to raise the light some, so I did raise it a little. After the second "day", they had drooped again. They Did recover during the one "night" cycle before drooping again when I checked this morning just before lights went out.

I have good air flow. It is a 3x3 with a 400 cfm Hydrofarm fan. Temp was at 79 at the highest with 51% humidity.

I am thinking I need to raise it some more, so I did. It now sits about 15 inches from canopy top.

Does HPS generally need to be further away than MH? It based significantly more lumens, so that is my thought.

That said, this is my first grow, so I would like the experts to weigh in. Please help...plus rep for all responses!

here is a few charts:

View attachment 2647661View attachment 2647662


but it depend on a lot of stuff, like if your running a cool tube/hood ? I could keep my 600W HPS at 12-15" with a cool hood on it, with out, it was more like 20"
at 20" with out it I had about 5,000 foot candles according to my light meter, with the hood at 12" I had +6K

btw
is the bulb new or used ?

New bulb in an air cooled hood. Thanks for the charts.

Any other thoughts?

+ Rep!

What is the amount of foot candles needed?

Is that the same as lumens?

It seems to me that a natural reaction to too much light would be to droop away.

Much in the same way plants reach and stretch when they don't have enough.

how old did you say your plant is/was when switching the light ?

also, it might take a few days to get em to get use to the new light spectrum I guess, if you have a hood on and good temps and plant`s is`t young seedlings I cant see a problem keeping them 12-15" tho you might want to start at 20" and move it down over a few days next time, insted of the other way around J/K

and yes 5,000 foot candles is what your looking for as a minimum, sun on a perfect summer day emits 10K

here is my 600W HPS with out a cool hood



about one foot away it provide 7-8K foot candles, 2 feet away +5K

I know Lumens or foot candles is`t the best way to measure light for plants (its Par) and my light meter is`t the top of the art so to speak, but it atleast give you a picture of how fast the light faint


here is a pic of my new LED fixture



about 7K a foot away and 5-6K at 1,5ft at plants top and no heat

and beside the 16x6500K led`s the rest is in perfect Par for plants/weed (620-700nM)

HPS only provide sumthing like 20-30% useful light rest is in spectrums that is`t to much use for the plants, so a lot of watt "lost" tho HPS spread the light a lot better then LEDs plants need to be right under them

They were about five weeks from seed, big, bushy, strong plants.

I figured they'd be able to handle the light. I'll raise it up even a but more when the lights come on and see if that helps.

Mine drooped for a few days after switching to hps. The lights were not too close
and the temps were fine.

They just need a few days to adjust to the new light sometimes.
I think it is because of the spectrum change but I could be wrong.

I have read other people post the same thing about switching before.

also plants have a cycle where they get used to. like plants may be droopy before lights out or right when the come on sometimes or be standing at attention during the day etc. or overwatering or being thirsty can make them droop.

When you switch to HPS do you veg for any period before switching to 12/12?

Turns out they just needed water.

So, learning point for me. As they have switched from veg to flower they are a lot more thirsty.

Fed last night when lights came on, droopy, and this morning they had popped right back up.

So, going to lower the light back down to maybe 12-15 inches.

for others who stumble upon this....don't be so certain it was "Just needing water" just because they changed after you gave them water after a few days. I have seen many strains be sensitive to light change. Just think you are going from 60K lumens to 90K, that is a 50% increase. Keep lights 12 inches higher when you make the switch, lower slowly over 7 days, and watch the watering, as you may have to give them water a day earlier due to the higher heat from HPS. I try to hold back the Nutes on the week I move them. Newbies tend to think switch to Flowering stage, hit em with nutrients, give em more heat...gardening is patients, you can rush it grasshopper!