A very basic lighting question

[OldManGrower]

Is it better to have your light suspended higher up at high brightness or lower down at a dimmer light level, assuming that the canopy coverage will be the same in each case?

[Mollisol]

I can't say which is better. As for myself my lights are always at full power. I adjust the height as the plants grow.

[SoOrbudgal]

Hmmm not so fast with my answer got me thinking dang it I've not burnt nor bleached bud yet. I'm still going to say i've got mine dialed down to 75% at 30" now. When my plants are in flower i'll move them closer to light till there 18" away and i go 100% on brightness. It's a 250watt from the wall.

[Rootsruler]

It depends on a few things. If you're trying to save electricity then dimmed down closer to the plant is better but you tradeoff the footprint the light gives off by concentrating it on a smaller area. If you run the light at 100% you can raise it and you'll get more light spread across the canopy but, again, depends on the light size and power and the size of the canopy you're trying to light.

[Going2fast]

Rootsruler is correct. But the concentration of the light comes into play also. I'm a 100% after flower start kind of guy. In veg I'll give them 50-75%. Then adjust height as needed. The higher the light the more the coverage you just have to listen to the plants for what is too much.

[Bluey]

I tend to take roots' approach.

My lights are currently running at 45% and height is about 29" and 31".

I am running them at 45% as it brings the room up to or really close to temp without the need for heater or AC to run unless ambient is really cold or really hot.

I'll try to manage it this way for a while as ambient temps are dropping. I won't need full light until after I have harvested the autos and flipped and stretched the photos well into flower. I may need to buy another grow light once I've scrogged these photos as they will be rather large and spread out. Perhaps an SE7000

[golfnrl]

Great question. It seems like its an issue of light spectrum vs light intensity. It makes sense to me that spectrum is more important than intensity. If that's the case, hanging the light lower with less intensity would seem to be less stressful and would produce happy plants and good yields. But IDK for sure. Last grow I followed the manufacturer's recommendations for distance from canopy (24" veg & 18" flower) and used the dimmer to keep from burning up my plants. Didn't get a good feel for it though cause the 100% sativa plants grew into my light with nodes too far apart. The dimmer was set on no more than 5 during veg, and 7 of 10 clicks during flower, so 70%? The yield was good . That makes me wonder how a lower vs higher light intensity affects node spacing. I didn't have the environment dialed in, the difference between day/night temps was to great and that contributed to the node spacing, but I don't know how much. Imma fittin' to find out though cause the next grow has started.

This convo makes me wonder if I need to go ahead and buy a light meter as several have suggested.

[Bluey]

I'd recommend running lights at 100%, as you'll get greater penetration and spread especially if you have lots of bud. I'd avoid it if you can't do it without heat problems or light stress because of ceiling heights

[OldManGrower]

Light "spread" or "area coverage" are not an issue for me as my light completely fills the inside of my tent. Penetration into the canopy could be an issue but can be dealt with via LST and defoliation. Just wondering if anyone had figured this out. Nebula/Sirius, would this be an experiment you could do?

[Bluey]

Well typically the higher the light, to a point, the more even the spread. If you go to websites like MIGRO or DrCoco and a few others that use proper testing methodology you can see what lights do and how it effects spread etc...and how wonderful reflective walls are

[Rootsruler]

I would check that spread with a light meter. What looks like adequate lighting will surprise you once you measure the light energy actually hitting your meter.

Typically you get a hot spot in the middle with a significant drop off towards the edges.

[12HourPower]

Rootsruler any recommendations on "good enough" light meters? Doesn't have to be accurate within +/- 1 photons. Just has to be reliable. I'm on the hunt for an infrared thermometer too.

[Rootsruler]

Agree. If I was testing out light rigs for a large commercial grow then I would invest in an Apogee meter but for a small tent grow I think a light app is more than sufficient. I have an android phone so I use Tent Buddy. If you have an Iphone you can use Photone.

[Bluey]

Photone is my preferred app also, but I also use PPFD Meter..

[12HourPower]

Bluey Rootsruler thanks. I was using a phone app. I just wondered about the accuracy.

[No3odiesShad0w]

I usually don't run my lights higher than 80% mainly to save on electricity but also to extend the life of the diodes on the grow light. (That's why I'm looking into extension cables for the ballast so I can mount it outside of the tent and off the board, decreasing the heat further and increasing longevity. Because I don't go higher than 80%, I do a lot of lowering and lifting the lights to give the plants the proper PPFD and DLI .
To test my PPFD, I use the Photone app on my S23 Ultra. It matches the par maps at suggested hanging height. I mentioned the app a few month back and a few ppl on this forum mentioned they too had compared their results with manufacturer PAR maps and found it to be accurate.
I haven't had any issues with light stress and I've been able to push plants up to 1200 PPFD and 55 DLI (with CO2 of course)

[Rootsruler]

You work out in a high CO² environment? CO² is really bad in high concentrations.

[No3odiesShad0w]

No no no I work out to get the CO2 higher. 1200ppm isn't a danger level and if I see the CO2 is high in the room then I get to be lazy but if I just cleared the room and I have fresh air with 400ppm then I'll do a light workout to get levels back to 1000ppm. Shit I got this tiny studio apartment....CO2 levels in here are always high when Windows are closed..... Unless I stop breathing. I don't have to really do much to have higher CO2 here. I would have never even known until I got a CO2 meter.

[No3odiesShad0w]

I think levels above 10,000 ppm are dangerous. 30,000ppm for only 10 min and 40,000ppm or higher is immediately dangerous to life. The 1500-2000ppm I get from a few squats is no problem at all.

[No3odiesShad0w]

This is the chart I was looking for. Even with 400ppfd, if you give some extra CO2, you can double what you would get. The pattern follows for all light intensity. But if you look at the saturated levels and compare them with all the other saturated levels, there's not much increase in yield. But if you compare 400ppm to even 800ppm of CO2 for any light intensity, you get at least a 30% increase. So according to this science, it's not about MORE POWER!!💪. it's about the right ENVIRONMENT 😉

[Rootsruler]

I understand how CO² works. Just not sure it's worth having to maintain it in my case. For CO² to work you have to maintain a particular level for it to be effective. If it goes up and down it won't have the desired effect although you've given me a brilliant idea. I'm going to move our bed into the lung room so that when the GF comes home I can tell her we need to have sex twice a day to maintain the CO² in the room. Thank You my Brother!!!

[No3odiesShad0w]

With that amount of action you might be overdo it. If you have a CO2 meter I highly recommend just put it in your living room or put it in your kitchen or whatever room you spend the most time in I guarantee you just by sitting there chilling there doing nothing like watching TV and by simply breathing your ambient CO2 is going to be 600+. So yeah I understand about maintaining CO2 levels but it's not like they're wildly dropping or changing they stay between 800 to 1,400 PPM That's kind of more or less the level I like to keep it at anything more is just oversaturated and could affect the stomata growing on young plants while anything less and I would need to increase the wattage on my lights to get similar results. So by being simply alive I'm creating and efficient environment for them to thrive without even really trying to lololol.

But yeah man Rock that boat! BE THE CO2 GENERATOR YOU KNOW YOU COULD BE 💪

[No3odiesShad0w]

You never know You might already be maintaining your CO2 levels just by being alive and maintaining your plants. Ink Bird sells a CO2 monitor for about 40 bucks which isn't terrible and it seems pretty accurate.

Also the picture of the chart was also in response to OP original question. Where light distance and/or intensity isn't the determining factor of yield per say. Other things factor in

[Bluey]

Just enriching the environment with CO² on its own will get you a little bit of an increase, but if you can bring up temps and PPFD you'll do much better.

Some say 1500ppm CO², 1500PPFD & 32⁰C is ideal for max yields. I've never tried it myself nor will I with this grow room. Just not worth the trouble.
Edit. You need to water heaps more and reduce the EC quite a bit too.