The Positive Effect of Diffused versus Direct Light on Plant Health, Vigor and Yields

Many years ago when I started growing indoors I made sure to provide as much indirect or diffused lighting to all plant parts. I did this with careful placement of movable side reflecting panels. Little did I know at the time how important diffused light was regarding production, just made a botanical guess, I guess. I would use side reflecting panels painted with 3 coats of thinned Behr's Ultra White latex paint, AND, paint the plastic floor white too. ( Plastic mulches, white or red, are known to increase production in the field and in greenhouse trials.) I even went so far as to cut panels of such a width that they would fit into a corner, slightly angled up, like 75*. Now that's anal! My yields have always been very good and the growth rate excellent, so fast that I have no choice than to flower within 3-4 weeks of the seeds breaking the soil's surface once they germinate.

Years later and after VERY extensive research and technical networking regarding glazing coverings choices for my new greenhouse, my choice of roofing material will be a diffused twinwall polycarbonate. Also, I have read studies from Cornell/Penn state regarding diffused versus direct and the tests always come to the same conclusion, diffused is best. Experimental studies show that crops with a high plant canopy and ornamental plants with a small canopy can utilize diffused light better than direct light. There are many diffusing products out there. Here's an example of one which addresses the benefits of diffused light over direct. http://www.polygal-northamerica.com/polymatte.php

8mm Polygal Polymatte™ sheet provides 77% light transmission and 99% diffused light. Plants create food from light and the type of light they receive is important. Plants exposed to direct light (no diffusion) produce a majority of their food from the top leave facing the sun. These leaves do most of the work while the shaded leaves do very little work. Diffused light provides light to all leaves and all leaves are able to photosynthesize resulting in more food production and healthier, fuller plant development and less stress on the upper leaves.

Click to expand...

Having said that, too many folks fail at lower canopy production, they do the lollipopping drills and such. They have not mastered light penetration. Reflected light can be your best choice, in fact using properly placed reflective panels a plant can easily receive 30% more light.

UB

I was shocked when i googled how much lumens does the sun produce ( 100,000 ) like 93 watts per Sq meter
I my self have have learned many things like even tho i run 1000 watt lights like 2 1/2 feet from each other, and plants seem like there beside a nuclear plant and grow crazy fast, it didnt matter how i did it i can not get lots of big buds on lower plant beeing canopy is covered my train of thought was pack as many plants in the room as u can even tho my yields are well over 1000 grams per watt thingy i believe i can achieve more by running less plants my indoor season is now over but my plans are to still run 10,000 watts but with no more then 40 plants

nice thread man! i do this kind of thing aswell except a little differently. i have a 4ft by 50ft roll of 2mil mylar, if you have some really thin wood or cardboard you can measure out a part of the growroom you want light reflected, cut out the wood/cardboard and tape/velcro/thumbtack the mylar to it, then set it up in your room.

Very cool post.I know this post is geared more to indirect lighting but I have a question about this which I asked in indoor growing but couldnt get a very clear answer. I got a bunch of 4ft 4 bulb T8's with the bumpy textured light diffuser panel in them(came out of a place that changed over to T5 fixtures). Im using 2 for seedlings right now, I was going to remove the panel to try to get more direct light to the plants but are you suggesting Im better off leaving that diffuser panel in?I checked with a (cheap) light meter and dont really see a difference with it or without just figure it has to be stopping some light.

Zaehet Strife said:

nice thread man! i do this kind of thing aswell except a little differently. i have a 4ft by 50ft roll of 2mil mylar, if you have some really thin wood or cardboard you can measure out a part of the growroom you want light reflected, cut out the wood/cardboard and tape/velcro/thumbtack the mylar to it, then set it up in your room.

Click to expand...

I bypassed the mylar and just went with very large painted cardboard panels.

WeedFreak78 said:

Very cool post.I know this post is geared more to indirect lighting but I have a question about this which I asked in indoor growing but couldnt get a very clear answer. I got a bunch of 4ft 4 bulb T8's with the bumpy textured light diffuser panel in them(came out of a place that changed over to T5 fixtures). Im using 2 for seedlings right now, I was going to remove the panel to try to get more direct light to the plants but are you suggesting Im better off leaving that diffuser panel in?I checked with a (cheap) light meter and dont really see a difference with it or without just figure it has to be stopping some light.

Click to expand...

Probably a moot point with a T8 but a diffuser might be important using a 1,000W HID.

Good post. I use a Super Spreader for this very reason. Time and again I noticed that the plants in the hotspot bleached out and didn't produce as well as those receiving weaker direct, and more reflected light did better. I bought a better hood, put up diamond diffusion reflective stuff and added the super spreader and I haven't looked back.

Sup Uncle Ben,
I dont want to be disrespetfull an dissagree with a ninja grower sutch as you.
But.......
Ive always thought different about Direct VS Diffuse VS specular lighting.

Teach us more.

Uncle Ben said:

Having said that, too many folks fail at lower canopy production, they do the lollipopping drills and such. They have not mastered light penetration. Reflected light can be your best choice, in fact using properly placed reflective panels a plant can easily receive 30% more light.

UB

Click to expand...

I agree light reflected to the side of the plants is great. I practice this in my lil cabnet with the most reflective surface i could get free, mirrors.
They are angled for specular reflection right at my plants sides by kicking the bottom of the mirror out a few inches.
Its like recycling light IMHO.
(I dont have big enough lights to light burn them at my distances , 175 MH an 150HPS)



Here are a few thoughts / questions on this of mine..... Could you give me you view?



1.Anything inbetween your light an the plant will block some of the light so diffusers eat some of the plants light?

2.Isnt Diffuse light or reflection weeker than direct light or specular reflection from the same source?

3.The more photons of light that hit my plant the better? (tell a critical point when cell start to die).
And I need all the light I can get in my little cab.
Do you think specular reflection from the mirrors would be better than Diffuse reflection off the white? (With my week hids, not sunlight lol.)

4.We use HIDs because we want Hight Intensity light so it can penetrate the canopy an give ALOT of light.
Wouldnt diffusing HID light (or sunlight in greenhouse) be counter productive?

5.Is diffuse better because its a Lambert scatter an is more evenly distributed?

6 If i flased you driving with a piece of white wood driving by nothing would happen.
If i flashed you with a mirror it would be BLINDING...
So how can diffuse white be more reflective an brighter (& deliver more photons for photosynthasis) than mirror or mylar?


IDK?

Go easy on me for asking lol
Brick top got mad when I asked this stuff I think.
lol.

Any opinions would be apprciated....

i use cardboard panels as well, to reflect light on the sides, made do with a flat white ones.

SCARHOLE said:

(I dont have big enough lights to light burn them at my distances , 175 MH an 150HPS)

Here are a few thoughts / questions on this of mine..... Could you give me you view?

1.Anything in between your light an the plant will block some of the light so diffusers eat some of the plants light?

Click to expand...

There are trade-offs. There might be some light lossiness due to a diffuser. It's up to the grower to determine whether or not a diffuser would work for them, reason why I made the comment I did in the previous post. We're talking intense light from the sun or a 1,000W HID as opposed to soft light from a 175HID or a fluor. Click on the Polymatte twinwall specs. Normal clear twinwall is 80% LT with 20% diffusion. The Polymatte is 77% LT with 99% diffusion. It's a no brainer. Bonus is there is cooling effect due to the lower solar transmission and the diffusion. That's what I'm after.

2.Isnt Diffuse light or reflection weeker than direct light or specular reflection from the same source?

3.The more photons of light that hit my plant the better? (tell a critical point when cell start to die).
And I need all the light I can get in my little cab.
Do you think specular reflection from the mirrors would be better than Diffuse reflection off the white? (With my week hids, not sunlight lol.)

4.We use HIDs because we want Hight Intensity light so it can penetrate the canopy an give ALOT of light.
Wouldnt diffusing HID light (or sunlight in greenhouse) be counter productive?

Click to expand...

Per my original post, diffused light from high lumen output sources reaches more plant parts, it excites more chloroplast material. Add in good reflecting panels and you've got a winner. If you look at page one of my topping method, you'll see how I sandwiched panels in the corners - 3rd photo.

Brick top got mad when I asked this stuff I think.
lol.

Any opinions would be apprciated....

Click to expand...

Us ol pharts get impatient with those that appear to not do their homework.

Good luck,
UB

Thanks UB.
The new acrillic glazing stuff is dam cool.
Its going to take over the industy somday an glass window may be obsolete.
We sell it occasoinaly to folks for green houses huge sunroofs / Skylights and more..

We ger ours from Regal plastics , the boss is a tight ass so id bet they are about cheepest.lol
But many sell about the same suff.

Ps
After years lawn mowing I have noticed how Under the trampoline were plants get less light, they grow better.
Those cooking in mid summer sun grow slow.
I believe the cooling effect is very real when it realy hot.

Wow, interesting stuff. I use LED's which work great for the top 4-5 inches of canopy but end up having to lollipop since the light doesn't penetrate well.

Do you have any advice I could employ to help fix that?

QueefCollins said:

Wow, interesting stuff. I use LED's which work great for the top 4-5 inches of canopy but end up having to lollipop since the light doesn't penetrate well.

Do you have any advice I could employ to help fix that?

Click to expand...

Other than reading my first post, use a HID. I'm not singling you out, but if I can grow stocky buds down to the lower levels, you guys should be able to too.

UB

this info is dead on. outdoors in Texas in July, if you're under 50% shade cloth you're winning over direct sunlight, especially with indica and indica doms cuz they were evolved in much less intense light environs and can't handle the blazing Texas sun (yes, it burns hotter on Texas, don't ask me why, but it does) and I've always gone by the dictum that the sun produces as much light as 10 1K bulbs per sq meter. that's super overkill indoors under any circumstances that I've encountered. so 50% shadecloth is awesome for reduction & diffusion in extreme sunlight conditions.

QueefCollins said:

So no helpful advice then. OK.

Click to expand...

That was good advice..you just do not like the answer...the way to get canopy penetration is HID...get an hid source and use your leds as side lighting

Namaste'

QueefCollins said:

So no helpful advice then. OK.

Click to expand...

You did receive helpful advice. You need to upgrade your lighting so it will be adequate to supply the lower portions of your plants with sufficient light. How you do it is up to you. Purchase a sufficient number of LEDs to use at different levels of your plants and surround them with LEDs or add a ton of CFLs at various levels or switch to HID lighting, a minimum of 400-watts, though higher would be better, as your main source of lighting and use your LED for supplemental lower lighting.

if you are growing in a sea of green or scrog, then wouldnt the canopy be so thick that no light gets through to the bottom. then there would be no light to reflect onto the bottom branches.also because of the inverse square law, the amount of light decreases exponentially the farther away from the bulb that you get. so is it better to make your canopy as thick as possible and have the majority of your growth closer to the light where there is more lumen, or is it better to thin out the canopy to allow for light to reach the bottom branches which is not as many lumen? which way will give the best yield?

SCARHOLE said:

Sup Uncle Ben,
...

I agree light reflected to the side of the plants is great. I practice this in my lil cabnet with the most reflective surface i could get free, mirrors.
They are angled for specular reflection right at my plants sides by kicking the bottom of the mirror out a few inches.
Its like recycling light IMHO.
(I dont have big enough lights to light burn them at my distances , 175 MH an 150HPS)
...
Any opinions would be apprciated....

Click to expand...

Glass ABSORBS light!
What is a mirror?
A mirror is glass (which absorb some light), put in front of a reflective surface (some metal). So the light has to go through the glass, which absorbs light, TWICE just to reflect the light back.

Ditch those mirrors, and get some Mylar.

Also, even if one had a 100% reflective surface, light would still fade exponentially.

i have a 13 watt soft white CFL I'm flowering with but I'm not really getting good big colas, i have 28 plants under it and its about 6 feet away from the canopy so i can get an even light distribution. Uncle Ben, tell me want i can do to increase my yield and quality using "this light" with these plants.

but all jokes aside, this is a pretty interesting subject. got any pics of your green house UB?

was just hoping it would make a few ppl smile is all, no need to get mad =(

Justin00 said:

i have a 13 watt soft white CFL I'm flowering with but I'm not really getting good big colas, i have 28 plants under it and its about 6 feet away from the canopy so i can get an even light distribution. Uncle Ben, tell me want i can do to increase my yield and quality using "this light" with these plants.

but all jokes aside, this is a pretty interesting subject. got any pics of your green house UB?

Click to expand...

Add another 13 watter or a 60W incandescent with an aluminum foil jerry made hood, shiny side out. You'll surely double your yields.

No pix of the greenhouse.

Not getting good yields happens to be the inverse of one's lack of experience and reliance on techno talk and theory.

UB