LED boards & the hotspot

Kassiopeija

Kassiopeija

Well-Known Member
Hello fellows,

now that diode tech makes it possibly to basically fill the entire tent"sky" with thousands of small "suns" I wonder why it's still not possible to do away with the central hotspot, that, basically is the result of too much diodes converging at the center but relatively less at the sides. When, in fact, the sides/corners where -or are- always less illuminated, sometimes even just by half of luminosity...

Here are some crudely montaged sheets where I illustrate the median distance of light rays under a board setup in comparison to COBs (their technological forerunners, not wanting to promote them now, just to illustrate an example)

Side view:
Image2.png
Average light distances:

COBs to pot1: 8.25cm
COBs to pot2: 7.0cm

Board to pot1: 9.3cm
Board to pot2: 7.8cm

Distance increase from board to COB: 12.7%


Top view:
Image1.png
Well, it doesn't take much imagine that one can use 4 strong COBS and place them in such a way in a tent that this tent is illuminated out in an almost homogenous fashion, by just driving the COBs equally on the diagonals, until the grade of light reflection or overlapping reaches equal numbers.

One can't do this with boards.. but maybe strips? Wouldn't it be possible to construct a board/bar that simply has less diodes to the center, and a tad more to the outside? Because, we know that reflection also causes some losses (a cheap tent may loose up to 30% upon first hit)...


Example:
H6f8a80b0fef34d159b4ba11fd80a3161t.jpg_640x640.jpg
At the closer settings the spot in the middle is +207% [!!] more luminous than the side, and +395% [!!!] more than the corners.

Ironically a good Avenger-hood with a big spreader underneath is going to show better results than this above!
So basically technology did take a step back while trying to evolve and loose an ability, instead of mastering this problem - which it could.

Coming from a HID/outdoor growing history I'm well versed in the problems with different & unnatural lightlevels, yet now we can place diodes all over the place, but still the same old problems remain... unsolved... just cut out in the middle and repatch at the corners...

"Intelligent diode placement"... even in an open industrial fashion where many boards are connected to illuminate a huge canopy such an emphasis to open up the array would be helpfull in proper light distribution.
 
E

end_of_the_tunnel

Well-Known Member
I think a lot depends on scale of area being illuminated. The larger the space the easier it becomes to avoid central hotspots, through careful placement of board, strip or cob elements. Hard to give a blanket statement, size and intensity of hot spots can vary case by case. Individual plants growing up and through strips is a classic example. Compared to a guy with some 4 board fixture and not enough headroom. Even plant count for given area should or could be a consideration. A mass of smaller plants exposed to a hot spot might suffer, but what about a tree under the same light? That tree might offer compensating growth on parts not exposed. YMMV. Can understand wanting to have even spread, but do not think there is a one suits all solution. People just have to work with whatever their choice of board, strip or cob.

One example, I think it was @Airwalker16 who highlighted a board that attempted to spread diodes out different, but do not see this being as efficacious a solution when board numbers increase. ( hope A16 is safe and well, not been on since the 7th)
Another I saw was a build by graying.geek. It was reading this guys thread that highlighted the hot spot issue to me and made me more aware.

Bridgelux EB-series on a 2' x 4' SCROG

@Page { margin: 0.79in } p { margin-bottom: 0.1in; line-height: 120% } Week 6 of 12/12. Predictably, after getting my wiring corrected (thanx, all!) I burned some of the pistils in the middle of the scrog where the light was too intense. Here’s a quick shot: Not a big deal at this point. Only...
www.rollitup.org

IES files and software to use them seems to be the way to address and accurately map. Theres a whole industry that makes a living using them.
 
N

NapoleonBlownapart

Member
@Kassiopeija I feel the same about QB boards and cobs. Cobs gives an excellent spread in a grow tent hung like this 1594983886658.png

I grew like this without lenses. Now I´m transitioning to a QB-build, but I´m still not sure if this will be better than cobs, even with a blanket of boards at much higher efficiency, maybe 15-20% more lumens/watt compared to my old build. I have a feeling that these boards throw way to much light sideways. Anyways, I will try this build and see what happens.

24boards.PNG
 
Kassiopeija

Kassiopeija

Well-Known Member
NapoleonBlownapart said:
@Kassiopeija I feel the same about QB boards and cobs. Cobs gives an excellent spread in a grow tent hung like this View attachment 4626750
Click to expand...
this is almost a perfect example how to do this, can you see how easily he can move the lights to basically any meaningful position? The 8 light setup allows for 4* 5500k for veg and just add another 2200k for flower. And there is still space for an UV fixture at the center... and these lenses give splash protection and also focus light more thoroughly to where its needed... (actually them Mars Hydros noticed that too lol) ... but you expect that the many cooler diodes will be more efficient to turn electrons into photons, that's for sure. And since the light comes from more angles is going to offer extra penetration power... and you'll be able to decrease the distance also a bit.

NapoleonBlownapart said:
View attachment 4626752
Click to expand...
so how much minimum distance you gotta keep with this setup? no doubt there will be higher luminosity at the center, as everything is spread out equally... I wonder if it would equal out if you make 6 out of the center 8?
 
N

NapoleonBlownapart

Member
Kassiopeija said:
so how much minimum distance you gotta keep with this setup? no doubt there will be higher luminosity at the center, as everything is spread out equally... I wonder if it would equal out if you make 6 out of the center 8?
Click to expand...
I am hoping for a minimum distance of no more than 35 cm(14 inches).

24boardsred.png

The eight boards in the middle will be driven separately from the boards lining the tent wall. In total, 6 HLG-240H-48B or A-type drivers. Each driver powering 4 boards at a maximum of 60 watts each. If the light gets to intense in the middle, I will dim them down slightly.

I have played with other setups in sketchup like this one, but I believe more diodes spread out is better.

20boards.PNG
 
cobshopgrow

cobshopgrow

Well-Known Member
at 35cm your board light config will shine compared to the Cobs.
simply take a luxmeter and go from cob to another at 35cm, easy to see, there will be quite some drop,
if the used lense is focusing it should be even worse with the lense.
to get the same spread as the boards you will have to hang the cobs higher, means more losses on the wall.
these middle power leds mostly have a 120 degree angle, so theyrel focusing a bit.
penetration just comes from light reaching the plant over different angles.

i just had a quick look at the light linked.


its maybe not the best to take a non suqare board light and compare it on a square par map, the corners have to suffer a lot this way.
youre of course right that this isnt the optimal spread for a 4x4 taking this arangement.

but once you spread out the boards better in a square like you did in your COB example you would have a better result then with COBs at the usual hangings heights.
taking the first best strip light from alibuba showing allready a better spread.



practically i used a Cob fixture as a Board and a Strip fixture i measured the light distrubution on all of them.

the strip fixture wins, but just by a slight margin over the previous used board fixture which where also spread out well and using tons of diodes.
with the board light i left the middle free and with the strips i concentrate them slightly to the edges and use a lower strip count in the middle to avoid hotspots.
the COBs loose quite bad compared to both regarding the spread at hanging heights one use in smaller indoor tents, there is quite some drop of intensity in the middle of 2 cobs at 35cm.

in the end all are leds, cobs, boards,strips.
in the case of strips n board even the same diodes, rest is more a matter of placement and spread.
 
1

1212ham

Well-Known Member
NapoleonBlownapart said:
I am hoping for a minimum distance of no more than 35 cm(14 inches).

View attachment 4626765

The eight boards in the middle will be driven separately from the boards lining the tent wall. In total, 6 HLG-240H-48B or A-type drivers. Each driver powering 4 boards at a maximum of 60 watts each. If the light gets to intense in the middle, I will dim them down slightly.
Click to expand...
I like the design, will be following along. I suggest drivers with AB dimming, the best of both worlds and they only cost a dollar or two more.
 
N

NapoleonBlownapart

Member
1212ham said:
I like the design, will be following along. I suggest drivers with AB dimming, the best of both worlds and they only cost a dollar or two more.
Click to expand...
Never heard of the AB-drivers before. Will definitely get them. I watched greengenes and growmau5 back in the day on youtube, and I dont think they ever mentioned this type of driver. Same with ledgardener, he never made any videos about the AB driver type.
 
Airwalker16

Airwalker16

Well-Known Member
end_of_the_tunnel said:
I think a lot depends on scale of area being illuminated. The larger the space the easier it becomes to avoid central hotspots, through careful placement of board, strip or cob elements. Hard to give a blanket statement, size and intensity of hot spots can vary case by case. Individual plants growing up and through strips is a classic example. Compared to a guy with some 4 board fixture and not enough headroom. Even plant count for given area should or could be a consideration. A mass of smaller plants exposed to a hot spot might suffer, but what about a tree under the same light? That tree might offer compensating growth on parts not exposed. YMMV. Can understand wanting to have even spread, but do not think there is a one suits all solution. People just have to work with whatever their choice of board, strip or cob.

One example, I think it was @Airwalker16 who highlighted a board that attempted to spread diodes out different, but do not see this being as efficacious a solution when board numbers increase. ( hope A16 is safe and well, not been on since the 7th)
Another I saw was a build by graying.geek. It was reading this guys thread that highlighted the hot spot issue to me and made me more aware.

Bridgelux EB-series on a 2' x 4' SCROG

@Page { margin: 0.79in } p { margin-bottom: 0.1in; line-height: 120% } Week 6 of 12/12. Predictably, after getting my wiring corrected (thanx, all!) I burned some of the pistils in the middle of the scrog where the light was too intense. Here’s a quick shot: Not a big deal at this point. Only...
www.rollitup.org

IES files and software to use them seems to be the way to address and accurately map. Theres a whole industry that makes a living using them.
Click to expand...
My father passed away and my whole setup had to come down. I've lost a lot of motivation to even get on here anymore. Just makes me wish I was still growing... I appreciate the looking out.
 
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