Hps height 400w

Ok im confused with the 12" height,if i put my light that close im pumping out 90000-100000 lums so my 3 light apps tell me on my phone.I read post about other people with 400s and you get so many different answers from 6' to 3ft.You have people say do the hand test and i do but still way to high on the lums and im going by what all the experts say the lums should be for each stage of plant.My plants are 24days old and lowered my light 4days ago at a height where im getting about 37000 lux and saw a big improvement.How many of you are doing 12inches and at what stage did you lower it to that

Bare bulb or glass hood/cool tube? 400 HPS puts out maybe 50k lumens at the most btw..

Drop That Sound said:

Bare bulb or glass hood/cool tube? 400 HPS puts out maybe 50k lumens at the most btw..

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Then my apps are wrong our not calibrated right.I think i should probably learn about par levels.

lurchin1 said:

Then my apps are wrong our not calibrated right.I think i should probably learn about par levels.

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Probably not calibrated right. I tried a couple of those and couldn't find my phone on their calibration list so got rid of them. Readings were all over the place even outside in the sun.

I just use a little light meter on on of those cheap 3-in-one plant probes to compare the output of the light with what I know it should read with a known light source. Arrange the plants so all are getting decent levels. Don't need anything fancy to use that thing.

I have one of those 3 in one I'll try that,cheers

Lux meters are cheap.

My rule of thumb for HPS/MH/CMH is to, put the back of your hand under the light and move it closer so it becomes uncomfortably hot, then slowly move your hand away until it's only warm, that is the minimum distance for your light.

Good luck

Get it as close as you can. Those phone apps are very unreliable. They use the camera on the phone which can vary significantly based on the model of phone. I run a 600 watt in a sealed hood and can get it closer than 12 inches from the top of the plants without any issues.

When I had my 400w back in the day It was air cooled with glass, and I had plants grow into the glass during early flower. I kept having to raise it up until finally they stopped getting bigger and my light was only about 4-6 inches above them.

Hugo Phurst said:

Lux meters are cheap.

My rule of thumb for HPS/MH/CMH is to, put the back of your hand under the light and move it closer so it becomes uncomfortably hot, then slowly move your hand away until it's only warm, that is the minimum distance for your light.

Good luck

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I do go a little more high tech than the little light meter or the old back of the hand methods. I use a laser thermometer to see just how warm the top leaves really are. With skin temp being around 93F what feels warm to the back of the hand is that or more and I like to make sure the leaves are a little cooler than that depending on room temp. If the leaves are constantly warmer than that then they transpire more water to keep cool which brings up more nutes that will get stored in those leaves and eventually cause burn from toxic salts buildup. I've seen many examples with growers asking why those upper leaves are burning but lower ones are just fine.

Infrared or just the light being too close will cause that over time even with all else being fine.

With the very low humidity I've been dealing with for over 20 years here I have to watch out for that happening. Running lower ppm helps prevent it.

xtsho said:

Get it as close as you can. Those phone apps are very unreliable. They use the camera on the phone which can vary significantly based on the model of phone. I run a 600 watt in a sealed hood and can get it closer than 12 inches from the top of the plants without any issues.

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I've had that chart for years and didn't think to put it up. Good one!