Top bin COB comparison

Thanks shrugs. I am actually a big fan of COBs and I will never go back to growing under HPS again, but I'd still rather see actual facts instead of incorrect/outdated figures. The reason many growers despise/distrust "led" is because the people selling led fixtures have been lying and many still do. I feel it's our duty to make sure we keep our facts straight so we can convince people instead of having them scoff at us for telling obvious falsehoods. Cree and Bridgelux COBs are good enough to beat HPS on their own merits.

People go through all kinds of lengths to squeeze a few more photons out of their COBs, often at extreme costs, but suggest to invest a few bucks in reflective walls and I'm crazy?

I did easily get 1g/W from my HPS up to 1.2g/W when I used a lower PPFD (ie larger grow area). So you can dismiss me for raining on the COB parade or think "Hey how did he do that then? Maybe the guy has a point.".

When you see those PPFD matrices for the Gavita 1000W it's clear that only around 40% of the light hits the measuring square (ie doesn't hit a wall) over a 5'x5' area or even only 25% over a 4'x4' area. That means almost 2 thirds or three quarters of the light will hit a wall first. Imagine losing half of that because of poorly reflecting walls? You'd be left with only the amount light that a 650W HPS emits. So that's not a fair comparison of the fixture.

Of course with cobs or leds, especially with reflectors/lenses mounted, this is much less of an issue, but you'd be surprised how much you can still gain with reflective walls. Especially if you ditch the reflectors/lenses on the COBs.

COB light builders will find diy to be a major factor. Some will eventually cater to that market. Top quality 3w and 5w lights make no less light or flowers than they ever did. COBs have taken dozens of connections and reduced it to a few with quick connects on some. A machine shop is not needed to make an effective light. No specialized equipment. More light also but this is rapid change in many areas. But, the best of the last non-cob lights still kill it.

wietefras said:

When you see those PPFD matrices for the Gavita 1000W it's clear that only around 40% of the light hits the measuring square (ie doesn't hit a wall) over a 5'x5' area or even only 25% over a 4'x4' area. That means almost 2 thirds or three quarters of the light will hit a wall first.

Click to expand...

I'm wondering how you come up with such numbers. My impression is that they're simply pulled out of a hat.
Gavita states 2100 µmol/s for Gavita Pro Plus 1000W EL DE, that is only about 360 µmol/s/m^2 averaged in 4x4 had we assumed only 25% of the light hit the square and no reflector losses.

wietefras said:

When you see those PPFD matrices for the Gavita 1000W it's clear that only around 40% of the light hits the measuring square (ie doesn't hit a wall) over a 5'x5' area or even only 25% over a 4'x4' area. That means almost 2 thirds or three quarters of the light will hit a wall first. Imagine losing half of that because of poorly reflecting walls? You'd be left with only the amount light that a 650W HPS emits. So that's not a fair comparison of the fixture.
.

Click to expand...

but that is the point IT IS a fair comparison. every bounce or reflection has light loss. we want to know how well a light performs, NOT how well you can design the rest of the grow room.

sub'd
I'm a lurking sponge seeking COB wisdom

I was lurking as well and decided that was what I should've kept doing but now wietfras' reply doesnt make sense with my original post missing. And he was making sense before so let me rectify... If I remember correctly, what I posted was: @wietfras, thank you for your efforts and nevermind the strawmen. And something about being levelheaded

Context matters...

BTW I figured you were a big COB fan wietefras thats why I appreciate your candor especially

Also a big thank you to SupraSPL

alesh said:

I'm wondering how you come up with such numbers. My impression is that they're simply pulled out of a hat.

Click to expand...

Like I said, calculated from the values of those PPFD matrices. Flat plane integration (on that subset) and some interpolation to fill the blanks.

Gavita states 2100 µmol/s for Gavita Pro Plus 1000W EL DE, that is only about 360 µmol/s/m^2 averaged in 4x4 had we assumed only 25% of the light hit the square and no reflector losses.

Click to expand...

Exactly. So what's your question?

I went with 1800umol/s though (after reflector losses) and then 312umol/s/m2 is 25% of the light (which hits the 4'x4' square). With the matrix @36" showing around 320umol/s/m2 average.

@PurpleBuz, A light designed to have a large footprint in order to overlap nicely with surrounding fixtures needs reflective walls when you confine it to a small space. So having reflective walls is part of using it properly I would say. Or you will be throwing away a large part of the light.

I don't get it issue though. You have no qualms spending $2500 on a led fixture, but will not consider spending a few bucks for some reflective stuff on the walls? Say you spend $250 on reflective walls (it's much less of course) and $250 for a 600W HPS fixture. Then you'd still spend $2000 less than on the AT600 and performance would be similar.

@shugs, Ah lol, I was wondering what happened to your post

Bonjour
When you said 1gpw under hps is it in soil?
I am about to replace my 600hps with 600w of led in my 4x4...and it will cost me about 1000$!
I too lives in an hot area...from may to october it is quite hot and as I do not have a/c I never grew indoor in summer...with cxb I will try!
I too am in the 0.7/0.8 range with hps in soil organic nutes! Never more...maybe the glass of my hodded reflector??
I already have 4 cxb3590 @1400mA (55w each) over a 3.5x3.5x4.5 and it looks very nice...2 weeks left!
So because you have better results than most of the growers with your hps if you switch to cob you will pull 1.7/2gpw (what I am sure is possible in hydro the good strain and grower!)
I guess a lots of experimented growers who already pull gpw and even more with hps believe that they're at the maximum weight possible...but if it is not in quantity cob will provide more density...!
I hope some will change their minds and will do a grow journal with awesome results to stop peoples arguing about how many gpw cobs could pull out!
CU

wietefras said:

I went with 1800umol/s though (after reflector losses) and then 312umol/s/m2 is 25% of the light (which hits the 4'x4' square). With the matrix @36" showing around 320umol/s/m2 average.

Click to expand...

Could you share the chart? The ones I saw are far from being 320 µmol/s/m^2 averaged, making me doubt your estimates.

BTW I agree that reflective walls are very important and possibly one of the easiest and cheapest tweaks in some setups.

wietefras said:

@PurpleBuz, A light designed to have a large footprint in order to overlap nicely with surrounding fixtures needs reflective walls when you confine it to a small space. So having reflective walls is part of using it properly I would say. Or you will be throwing away a large part of the light.

I don't get it issue though. You have no qualms spending $2500 on a led fixture, but will not consider spending a few bucks for some reflective stuff on the walls? Say you spend $250 on reflective walls (it's much less of course) and $250 for a 600W HPS fixture. Then you'd still spend $2000 less than on the AT600 and performance would be similar.

Click to expand...

Do not put words in my mouth I never said that you shouldn't use reflective walls. What I said is the performance of a light should be based on what light it puts on the plant canopy without extra measures that are NOT part of the light. Period end of story.

light that goes sideways away from the primary canopy that its lighting is not beneficial in most grow conditions.
The only condition that sideways light is bennefical without suffering major losses is in the center block of a much larger grow space. All outer rows, walls, tent sides and walkways lose light.

Why is this okay with you? How are you calculating the amount of photons that end up back on top of the canopy after bouncing off the walls?

You're assuming all of that light is just redirected back where you want it.

It's not.

Personally, I want my light to go in a direct line from source to destination. I want to be able to hang my emitters 12" from my canopy so I don't have to rely on a wall with unknown reflectivity to redirect 60% of the light that I'm paying for.

If anyone in this discussion is grasping at straws....it's you.

wietefras said:

That means almost 2 thirds or three quarters of the light will hit a wall first.

Click to expand...

lol prolly cause he is either a car salesman or a politician, forget the science winning a verbal debate is more important regardless of the truth and sanity.

So are you guys saying led lights do not cast light at the walls?
At all...

genuity said:

So are you guys saying led lights do not cast light at the walls?
At all...

Click to expand...

Unless you have some kind of reading disorder I'm pretty sure that you can figure out the answer for yourself.

alesh said:

Unless you have some kind of reading disorder I'm pretty sure that you can figure out the answer for yourself.

Click to expand...

So falsehoods...is what I'm reading. ....thanks.

genuity said:

So falsehoods...is what I'm reading. ....thanks.

Click to expand...

Could you elaborate?

If you need to be spoonfed....I'll be your nanny.

genuity said:

So falsehoods...is what I'm reading. ....thanks.

Click to expand...

alesh said:

Could you share the chart? The ones I saw are far from being 320 µmol/s/m^2 averaged, making me doubt your estimates.

BTW I agree that reflective walls are very important and possibly one of the easiest and cheapest tweaks in some setups.

Click to expand...

It's somewhere on the Growershouse website. I have it in a PDF, but I'll try to find it back.

:edit: It's on this page http://growershouse.com/blog/best-indoor-grow-light-test/

The 36" has a max PPFD of 481 and min of 239. Filling in the blanks I got an average of 318.

I took the 24" matrix to guestimate how much would fall on a 5x5 square (light lower would reduce the footprint compressing 5x5 into 4x4). Although thinking about it I probably should have gone for the 30" matrix. Or something in between. That would only increase the losses for the 5'x5' area though.

Santa works in mysterious ways. RIU nonsense vs WF nonsense... this should be fun.

wietefras said:

Most growers are also surface area bound though, so they care more about the increase in dry weight from the same tent than a slightly lower g/W ratio.

Click to expand...

Where have I read that before...

*Spoiler alert*
Real world scenarios do not apply to the led fans here wietefras. They have unlimited space, their reflectors suck, their imaginary hps bulbs suck, rarely have proper ventilation/exhaust (but instead use ac...) and when they claim to have doubled their yields switching from hps to led it's because they yielded 0.5-0.6 gpw under some half-assed hps setup.

genuity said:

So are you guys saying led lights do not cast light at the walls?
At all...

Click to expand...

Heh, no of course they also have light hitting the walls. Just a lot less. The AT600 has lenses on it so the light is bundled. It projects a small footprint and therefore hardly any light will hit the walls

Also with COBs you have a lot of them and some won't even be near a wall. The COBs are much closer to the canopy. The 1000W HPS is usually at 36" and COBs can be down to 8". That's a lot less wall being lit up.

I still think making sure that bit of wall is highly reflective will benefit your grown though. I personally rather make the walls reflective than install reflectors or lenses on the lights. That way only the light hitting the walls needs to be reflected. The rest can just go to the plants undisturbed

There are actually HPS fixtures that you can add extra reflectors to prevent light from hitting the walls so much. Like the Dimlux Alpha fixtures. They sell add-on reflectors thay you can mount on fixtures near the wall or corner.