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HID Height-Light Bleaching-Indoor Stealth Grow

PaganRich

New member
Afternoon all
I have a question. In the attached pictures you will see my main tent for my lasses through flowering. It has a 6" input fan, 2 x 600HID lamps in air cooled tubes attached to a 6" & a 4" inch exhaust fans (one per tube)and there is a 4" passive input tubing as the negative pressure is too much without (Believe it`s termed negative when the walls of the tent are sucked in when closed). The input fan is aimed at the ceiling towards the far end (left in pictures) of the tent to bounce the air around as well as a floor standing oscillating fan at the right end. Also, there is a dehumidifier that is turned on post watering and hours of darkness due to the hot air it expells which can increase the temp in the tent by 1c roughly otherwise off during lights on. Temps range between 25-28 and in a heatwave ( :D :D :D yeah, right ) has gone above 30. I now shut down in June/ July ish time as it gets too hot in the room as it`s a bit of a sun trap just outside in the garden. Due to the fact that I`m the only one living there and I live quietly I don`t need to clean the exhaust air and can open windows throughout the house though not the grow room however air conditioning is not a viable option due to running costs and pipes, etc.
Now, I use only compost teas to water and feeds, etc and use a half of standard recommended strength with great results (as can be seen with the pic of my orchids that I feed the mixture to as well and feeling tad proud of at mo :D )
There is no issues with calmag lockout. Airflow is very good and humidity around 40-50 on daily average. Watering every 3-4 days-roughly 1-2 litres per plant. Strains are currently Delhi Friend, Critical Kush, Honeysuckle, Red Diesel, Pineapple Chunks and Incredible Bulk. Girls go into the tent on the left side when I flip them and every 2 weeks 3 days move right a row roughly. Five rows, 3 full months-ongoing. A very sweet set-up for me. Not everyones way but it helps structure me.
Now, my problem is this: I started to get yellow leaves on lasses within a 3 foot area to the left inside the tent where the air from the input fan blasts downwards. It`s been very cold lately and I figure temps may have easily dropped below 10c and caused cold burn overnight resulting in all the leaves on the affected girls going yellow. When they were moved to the right the leaves turned back green again eventually though not fully.
Now though I`m having some girls go yellow all the way through from top to bottom but there`s no burning and they don`t fall off. Also, they go to harvest and yield well. The only thing I can think of is that with 2x600w in a tent 240x120cm.the issue could be bleaching. I had the lights at 16"s above the middle girls but have now raised to 20". My question is simply this: Do you guys think that 2 x 600 at 16" above canopy was too close, that 20" is the optimum preferred distance and will this impact (At 20 instead of 16) by decreasing yields? Also, could the 2 HID`s be `increasing` the overall combined light strength/ glare being given off. This is not a nutrient or watering problem.
Thank you for any input/ thoughts :)
 

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"Cannabis starts to saturate at around 500umols or 40,000 lux. The best range for photosynthetic efficiency is between 500-700umols or 40,000-58,000 lux. With the highest levels to be no higher than 1000umols or 80,000 lux."

From my article on light height. 12"-16" is roughly the 60-80,000 lux range which is the minimum distance you would want. 16"-24" is roughly 40-60,000 lux which is most effective for photosynthetic efficiency. However you must take into consideration the amount of radiation losses from having a light source too high. As such you want to balance the light source so that both the plants light utilization efficiency and distribution efficiency are satisfied. I use a really big and wide hood which provides great uniformity and distribution, allowing me to get closer and limit the radiation losses. Smaller hoods usually require higher fixture heights as their uniformity is not as good, creating high concentration areas.

It might be good to invest in a lux meter to quantify how your hood is operating.
 
DANGERDAN Thanks mate, that wide hood is beginning to look like a useful option/ idea. Have a lux metre and that shows I`m working around 35,000 at 20" however I may not get the bleaching...can you tell me what brand hood you use/ recommend please? Thanks for your input.
 
Pagan, If the leaves went yellow down below, then it couldn't be the lighting, could it? It's a puzzle to me, and all I can wonder is whether it's due to cold temps and fan together?
 
alltatup I must admit that was my thoughts....raised lights to above 18" for directly underneath which takes to 20" plants on the side so we`ll see but DANGERDAN recommeded this wicked hood which I may give a go
 
Your current hood looks to have a wide distribution, id say you could actually bring your fixture closer than mine. At 18" my fixture is 660umol or 55,000 lux.

There looks to be a lot of wasted light on those walls, a wide and deep hood like mine might not be able to get closer but it will surely help prevent any additional losses from sidewall reflections that your currently having.
 
DANGERDAN I have taken your advice and lowered to 18". That hood does look the business. Thank you for all your helpful advice...seriously tempted by that hood. Are they heavy?
 
They are heavy and big, only just fit in a 4x4 tent. They are one of the best if not the best reflector hood for light uniformity. There was someone over on another forum called pico who did measurements comparing many different hoods, the magnum bested them all. They arent cheap but if you want the best for sodium discharge, theres not much better. Reflectors are one of the biggest factors in lighting efficiency. Some of those wing reflectors waste a lot of light.
 
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