Need to move light when switching from MH to HPS?

[Megawattfarmer]

Getting ready to flower!

I am trying my first grow with a digital ballast switchable MH/HPS 400W. I have a light meter that I borrowed from work that showed about 3,500 foot candles at the top of the plants with the MH, which is listed at 35,000 lumens.

I just changed to the HPS, which is a agro bulb that says its 55,000 lumens and at the same distance measures about 8,000 foot candles. I would have to move the plants down about two feet to get the 3,500 foot candles of the MH.

Do I really need to move it that far? Anybody else just switch without moving?

I have moved them down a ways. Removed one tier of my shelf system. Now it is reading around 4,500 foot candles. Don't want to mess up at this point, but I don't remember reading anything about this.

 

[JJScorpio]

I am confused what you mean by moving them away? You should be able to get the light within 16 inches from the tops of the plants....

 

[Megawattfarmer]

I don't want to shock the plants by jumping up in intensity. I know that there are more lumens/footcandles with the HPS, but don't know how the lights compare in energy. I was afraid this wouldn't make any sense. I'm probably just being picky.

I understand that the HPS will have more energy in the yellow/visible sprectrum and will therefore have higher lumens per watt. I guess without knowing the exact PAR watts of the bulbs there isn't a good way to tell this. Just mostly wondering if anyone has had any plant shock from switching from MH to HPS.

I think that this grow has been so f'd up that I'm jumpy about making any changes. Time to smoke a bowl...

 

[JJScorpio]

Its not going to cause any problems. The suns intensity is not the same everyday and is much more powerful.

 

[subfloral]

i would just start them a little low if you are worried about it and in a couple of days move it up until it feels comfortable on the back of your hand after holding it there for 30 sec. being as close as possible... i wouldn't think that it would make that much of a difference though... not one that you should worry about...

 

[Megawattfarmer]

Sweet, thanks guys. I can't wait to start moving it closer and making big buds! It's pretty much a uniform temperature up to the glass that divides my cab. So I should be able to get them up to a few inches!!

 

[Dan42nepa]

my HPS was alot cooler then the MH i have them closer now then when I was veging under MH.