Mirrors under plants to boost light exposure?

Fenderbender said:
I keep looking, I just read a whole thing on Paspalum Dilatatum, but that's a C4 plant where abaxial side showed even higher CO2 absorption rates when lit on that surface.

And here this is from C3 rose.
Leaf optical properties : Rose leaves from different positions in the canopy profile showed similar optical properties in the visible spectrum. As example, Fig. 2 shows typical spectra of light transmission, reflection and absorption obtained in the middle leaves of the upright shoot (US-ML). Rose leaves lighted from the adaxial side showed low values of transmission and reflection of violet(400–455 nm) and blue (455–500 nm) light, slightly higher levels in the green region (500–580 nm), followed by a decrease in the red light (620–700 nm) and a drastic increase in the far red (from 700 nm). As a consequence, absorption was high from 400 to 500 nm and around 670–690nm, but showed a depression from 500 to 650 nm and a large drop from 700 nm (Fig. 2). Optical properties of abaxial side of leaves followed similar pattern as those of adaxial leaf side. However, light reflection and to a small extent also light transmission were higher for abaxial leaf side compared with adaxial, with consequent lower values in light absorption (Fig. 2).Averaged over the whole visible spectrum (400–700 nm)and leaf layers, rose leaves lighted from the adaxial side transmitted 4.5%, reflected 5.8% and absorbed 89.7% of the incident light (Table 1). Lighting from the abaxial side increased the average value of transmission to 5.60% and of reflection to 11.34%, with a consequent decrease of absorption to 83.06% (Table 1). Within the PAR range, green light had lowest absorption in both adaxial- and abaxial-lighted leaves, in all the leaf positions, because of increase in both light reflection and transmission (Table 1). Differences between the leaf sides were stronger in reflection than in transmission.

So is would an absorption rate of 83% not be photosynthetic?

and also penetrating green light is refracted back and forth within the leaf tissue, encountering the chloroplasts repeatedly and gradually being absorbed. This phenomenon is especially noticeable in the spongy tissue in the bottom part of the leaf, which is composed of amorphous cells.
So light absorbed from the bottom would bounce around as well and activate chloroplasts is what I'm thinking.
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Thank you. A lot of great information
 
bluter said:
cannabis leaves aren't particularly complex.
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Well yeah you only think they work from one side 😆 sure that book from uni isn't a bit outdated as I still can't find a word to support this. And at this point I'm not even inclined to believe a botanist who tells met this.
I went down a whole rabbit hole of under lighting.
Tests with Soybean, Rose, Olives, Grapes etc.. (all being dicots like Cannabis) show of course more net photosynthesise when only lit from the top and less from the bottom with the same PPFD but well there's plenty activity on both sides..but turns out photosynthesise can be higher when both surfaces of a leaf are simultaneously irradiated compared to when only one surface of a leaf is irradiated.
So Braddah Waiheesohai's picture with the bottom lights isn't that crazy after all.

"In a plant factory with artificial light, upward lighting is expected to prevent senescence and decrease in the photosynthetic capacity of the lower leaves in the canopy. Upward lighting may also increase the photosynthetic rate of a canopy by improving its photosynthetic photon flux density distribution"

But I guess the important thing is how much improvement is there.. with their test crop "The CPn increased by 1.08–1.13 times by combining downward and upward lighting due to the increase in the photosynthetic photon flux (PPF) of light incident on the canopy and the decrease in the spatial variation of PPFD on the leaves in the canopy. As the depreciation of lamps for upward lighting accounts for 7.5–9.0% of the production cost in a PFAL, even if the depreciation of lamps for upward lighting increased, enhancement of CPn by upward lighting would be cost-effective."

(Now I think of it, these guys might be doing research for people who want to sell entire lighting factories and have their software churn out see if you opt for the upward lighting there's x amount of return and we get to install thousands more fixtures :) )

But yeah that wasn't Cannabis and if it were is that worth it? What would that increased ratio translate to yield wise?
If I times my yield by 1,13 that's not really doing it for me :p
And how much extra electricity is consumed?
Probably not worthwhile for the home grower.. as well I'm not doing halls full of plants so that a a couple percent extra becomes a ton more and have all my costs deducted.
Although if a couple of not too high wattage leds placed close by from the underside does fill out the bottom a lot more and keeps it from dying off it might be interesting to give it a try sometime.
The buds in Braddah's picture do look pretty mighty & juicy.

And then this crazy study.. oh yeah leaves sway in the wind.. let's simulate that.
"Previous investigations on photosynthesis have been performed on leaves irradiated from the adaxial surface. However, leaves usually sway because of wind. This action results in the alternating exposure of both the adaxial and abaxial surfaces to bright sunlight. To simulate adaxial and abaxial surfaces alternant irradiation (ad-ab-alt irradiation), the adaxial or abaxial surface of leaves were exposed to light regimes that fluctuated between 100 and 1,000 μmol m−2 s−1. Compared with constant adaxial irradiation, simulated ad-ab-alt irradiation suppressed net photosynthetic rate (Pn) and transpiration (E) but not water use efficiency. These suppressions were aggravated by an increase in alternant frequency of the light intensity. When leaves were transferred from constant light to simulated ad-ab-alt irradiation, the maximum Pn and E during the high light period decreased, but the rate of photosynthetic induction during this period remained constant. The sensitivity of photosynthetic gas exchange to simulated ad-ab-alt irradiation was lower on abaxial surface than adaxial surface. Under simulated ad-ab-alt irradiation, higher Pn and E were measured on abaxial surface compared with adaxial surface. Therefore, bifacial leaves can fix more carbon than leaves with two “sun-leaf-like” surfaces under ad-ab-alt irradiation. Photosynthetic research should be conducted under dynamic conditions that better mimic nature."

So are there stroboscope grow lights? Sync them in an alternate pattern and flash my crop from above and below for heavy dynamic conditions 😆 She might also get tricked into thinking she's swaying super hard in the wind and grow extra big and strong..

Hmm all this worry can be negated by just scrogging short & wide so everything has plenty of light available, doh!
 
there is not a single commercial greenhouse anywhere that lights the bottom. i've seen 4 separate legal facilities, the techs there would laugh their asses off over lighting the underside.

one place used vertical growing for seedling to early veg. it's essentially a shelf grow on steroids. under those conditions many plants would be real close to being exposed almost 360. the underside is not lit, but there is so much bounce light it may almost be the same as if it is.

from veg forward they are grown under standard lighting conditions from above. it's important to note there is a lot of light in those facilities. you never see a shadow at all in those rooms when you walk through them.
 
Yeah for cannabis probably not.. I do think it might be applied or some would like it applied in vertical farms for food where you have them growing smaller crops stacked 10 high, cause it's research surrounding plant factories and I don't think I'm far off with them wanting to sell a whole lot of supplemental lighting for these types of installations.

And well in a small tent under lighting seems more feasible than side lighting to experiment with as you well you can only hang like very light bars which they can grow against if you use side lighting in a small space.
I'm hardly using the space in the current grow so I could hang the Sanlight on top and come in with the Mars from the side and then rotate the plant around each day.
 
Fenderbender said:
Yeah for cannabis probably not.. I do think it might be applied or some would like it applied in vertical farms for food where you have them growing smaller crops stacked 10 high, cause it's research surrounding plant factories and I don't think I'm far off with them wanting to sell a whole lot of supplemental lighting for these types of installations.
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the guys with the vertical cannabis farm also have vertical farms producing fresh herbs and spices all year round for the grocery market.
it's pretty amazing. the lights are in fixed positions and the plants rotate around and past them as they grow and mature. they are harvested as they reach the bottom and the racks are replanted.

it's pretty close to being lit 360. nothing is technically lit from the below, but you won't see a shadow anywhere. not from the plants, the racks, people working, nothing at all.


Fenderbender said:
And well in a small tent under lighting seems more feasible than side lighting to experiment with as you well you can only hang like very light bars which they can grow against if you use side lighting in a small space.
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i do know folk who side light and have seen one small legal facility that made use of side light. i do think it helps.


Fenderbender said:
I'm hardly using the space in the current grow so I could hang the Sanlight on top and come in with the Mars from the side and then rotate the plant around each day.
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that sounds like a great approach.
 
cannamuffinman said:
My lighting set up is more to get light to the lower leaves that are shadowed when the lights are only from above. It seems to encourage thick and wide branches that are less " leggy" than those that grew under a single light source from above.

I never took biology or botany so I only know what is directly applicable to growing cannabis and in new that too. Trying for maximum yield in my limited space with weaker than optimal wattage. I appreciate all the knowledge being shared.
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Your ViparSpectra PAR 700 LED is rated at 700 watts but the rating is not the same as the actual wattage output. A web site called "ledgrowlightsdepot" reviewed the light and listed a wall draw of 320 watts which is close to the usual 50% wall draws in relation to factory ratings.

I have read many times here that the recommendation is 35 watts per square foot and your 3X3 tent is receiving that amount so no major problem that I can see. If your mirrors are more reflective than the walls of your tent you could consider using them to reflect light to the sides of the plants where there will be a better chance of the light energy hitting the sides of the plant canopy. Less distance the light has to travel before it hits the leaves so a better chance it will help promote some extra growth. Lot better than trying to get a decent amount of light by placing the mirrors at soil level.

You just have to come up with a way to mount them so they do not damage the tent walls.
 
mirrors have never been recommended as a surface in a grow area. professionals avoid them altogether. they do not reflect in the manner folk assume and cause hotspots and all sorts of trouble.
 
cannamuffinman said:
I'm only looking for to get the most from weaker than optimal wattage and bring some light to lower leaves ( not the undersides) but I get it. So the best I can do is reflective surfaces on the sides. Thank you all.
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your best bet is flat white paint. i use relflectix if i don't have a paintable surface or can't otherwise change the wall covering. paint will always be the best covering.
reflectix is probably 2nd best. it's a bubble mylar product. if you use a mylar make sure it has a texture and is not a flat sheet or panel.
 
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