Back in the game.....need 2x4 lighting advice!

[HotBunz]

I run this light at full.

I had to raise it to 36" to get 45 DLI at 18 hours.

The center hot spot is quite a bit wider at that height. The rest of the light bounces off the walls, and there is some loss in each reflection (about a stop and a half) but it eventually bounces back to the plant or dissipates as heat.

Thank you for the info.

 

[Delps8]

I run this light at full.

I had to raise it to 36" to get 45 DLI at 18 hours

The center hot spot is quite a bit wider at that height. The rest of the light bounces off the walls, and there is some loss in each reflection (about a stop and a half) but it eventually bounces back to the plant or dissipates as heat.

Hmm, interesting.

Why'd you go to a 36" hang height? You're in a tent or a grow room?

This is a "greenhouse" light, designed to be strung across the grow area. As with all LED grow lights, as hang height increases, the PPFD map evens out.

How did you measure PPFD?

"about a stop and a half" - wow, someone talkin' ƒ stops!

 

[Drownomatic]

Hmm, interesting.

Why'd you go to a 36" hang height? You're in a tent or a grow room?

This is a "greenhouse" light, designed to be strung across the grow area. As with all LED grow lights, as hang height increases, the PPFD map evens out.

How did you measure PPFD?

"about a stop and a half" - wow, someone talkin' ƒ stops!

Grow rooms.

I have a meter, and the photone app.

They are pretty close.

 

[Drownomatic]

Why'd you go to a 36" hang height?

I want the light as high as possible, to get more light to the lower leaves.

Let me explain:

Light falls off as inverse of distance squared. This means that the closer the light, the more disproportionate the distance between the light and the upper vs lower leaves is. With the light high there is almost no measured difference 8" lower down the plant.

Now, light doesn't radiate from a point source alone on a grow light so in actual application the loss over distance isn't as bad as the formula predicts, but its still there.

So I turn my lights to 100% and set the DLI by adjusting the distance.

Temperature I adjust with the exhaust fan. I have the AC Infinity biggest humidifiers, and they hold whatever VPD I set them to.

 

[Delps8]

I want the light as high as possible, to get more light to the lower leaves.

…because raising the light evens out the PPFD map so PPFD values will drop in the center and will increase around the periphery.

It would be interesting to see what the 36" map looks like. Post'em if you got'ed.

If you're in a tent and 36" hang height doesn't that take away from the grow space? If you're using 36" hang height and if you've got an air filter in the tent (1'?) what size plants are you growing?

Let me explain:

Light falls off as inverse of distance squared. This means that the closer the light, the more disproportionate the distance between the light and the upper vs lower leaves is. With the light high there is almost no measured difference 8" lower down the plant.
Now, light doesn't radiate from a point source alone on a grow light so in actual application the loss over distance isn't as bad as the formula predicts, but its still there.

A grow light has hundreds of points (diodes) and, in many cases, there are lenses and/or a cover between the diode and the canopy so it would be pretty complex formula to calculate the light value on the canopy. As much as I enjoy a programming challenge*, I'd rather use a light meter.

So I turn my lights to 100% and set the DLI by adjusting the distance.

Temperature I adjust with the exhaust fan. I have the AC Infinity biggest humidifiers, and they hold whatever VPD I set them to.

AC Infinity for the win!

*I've been a software engineer for 30+ years including a stint for Apple so I have some insights into the issue

 

[Delps8]

Grow rooms.

I have a meter, and the photone app.

They are pretty close.

View attachment 1732870

"grow rooms" - one light or multiple?

What factor are you using with the Sekonic or is there a way to adjust it to compensate for the spectrum?

 

[Drownomatic]

"grow rooms" - one light or multiple?

 

[Delps8]

View attachment 1733551

Beautiful color. What strain is that?

 

[Drownomatic]

Beautiful color. What strain is that?

I believe that was Blackstrap.

 

[Delps8]

I believe that was Blackstrap.

That's quite something.

I've grown the "standard stuff" - Gorilla Glue, Gelato, and a few other common strains so the leaves change color as they age but everything else is just plain old green.