I recently switched from using a relatively inexpensive $150 1200 watt LED to a 400 watt Metal Halide/ HPS set-up.
For the second time in a row now it seems like my Plant(s) just want to keep growing and growing and growing and growing (you get the point) after switching from 18/6 to 12/12
I'll let the pictures do the talking as far as my grow set-up etc and I'll answer any questions you have later. I'm growing feminized photo-period white widow seeds from Nirv&^@ (AM I allowed to say?) I grew the same exact seeds with the LED with the same exact drip feed set-up and after 3 days I always saw white hairs every time like clockwork. I'm growing in a basement with a short ceiling so I only have 48" headroom from the growing medium to the 6 foot ceiling. That only gives me 30" for the plant + 18" minimum for the grow light. With the LED I started flowering at 22" and it was perfect. So I switch to a 400 watt MH/HPS set-up with a "wing" design vs a vented hood. My grow space has a 4" exhaust fan built into the wall and a wall mounted 12" oscillating fan. I know everyone is using tents now but I'm in a basement doing it the old school way I guess. I had no issues with the LED.
This time I wanted to make sure I had enough head room so I switched to the HPS bulb (red spectrum) and a 12/12 schedule on the 6th of May @10am when the light normally comes on I switched the bulbs and reprogrammed my digital timer to shut on/off at 10am/10pm (it was 10am/4am with the MH light)
Every single day since I switched bulbs/schedules my plant has grown 1" but I don't see any white hairs. This is now day 6 and my plant went from 14" to 20" I'm using old school general hydroponics flora series nutrients just like I always did before with the LED.
LASTLY... NOBODY but nobody disturbs my plants when they're sleeping. That room is pitch black! I used to develop film in that room in college (yeah I'm old) so no light gets in! Nobody accidentally turns lights on or shines a flashlight on my plants. Will the wrong HPS light / spectrum cause this? The last time I waited 13 days for 2 plants to flower. They hit 30" and I had to scrap them!! This is beyond aggravating. That's why this time I started flowering @ 14" (I can't recall the exact amount of vegging days) Like I said these are photo-period feminized White Widow plants. From the same exact batch I grew with the LED!
PS. Yesterday I switched from the "transition to bloom" mixture to the "Blooming" mixture.
PSS, Does it sometimes take 2 weeks for white hairs to show???
Like what I see as far as set up. First thing first...,light distance from canopy? From the picture it looks like it's too far from the top of the canopy.Just a little info about me. Starting indoor gardening in the 70's when all there were available were landrace strains we were smoking. Anyway.. I'm old school MH and HPS by choice and results. Light schedule is everything...,18/6 veg..., 12/12 flower. Once I switch light schedule I don't change spectrum until they are in pre-flower. You probably already know this but each phase of growth have different NPK requirements.
Light distance for 400 watt HID
Closest 12"... Sunlight 14"... Farthest 19".... Also you can use the back of your hand at canopy and if it is too hot for you then it's too hot for your plant or plants. Any questions please feel free to ask. Grow big buds