Sun exposure morning vs evening

I just harvested my indoor garden- except for one plant. I ended up moving her to my outdoor garden. I didn’t ease her into it though. My electric bill over the past two months was telling me I should be gardening outside during the summer and I wanted to shut it down.

A few of the leaves on some of the underneath buds really got fried. Only on the western facing side of the plant though. Which got me thinking.

My outdoor garden gets a lot more of the evening sun than morning. I wondered if any of you guys had any thoughts on the topic or any preference. I’m thinking the extra red might be good for flower production. But I guess I’m not sure if there’s much difference in the amount of red in the morning vs evening either.


@CurrDogg420 there’s more blue, ir, and uva/uvb during the afternoon during high light because of the angle of the sun and how light is filtered from different angles.

Early morning and late evening there’s less uv and blue but higher red and ir due to filtering.

It’s why the shorter the day is the more red and IR we get for our plants because the sun spends less time over head and more time at a filtered angle.

Long story short, the angle the sunlight hits the atmosphere changes how much and what light gets filtered. Kind of like using a diffusion screen for seedlings that blocks out the blue and uv so they don’t burn. When the sun is rising it is filtered, when it is high over head there is less filter, and when it is setting it is filtered again.

That being said, the reason you have more burning on the west facing side of your plants is because after high noon when the sun is at its peak it continues to move westward so the west facing side of the plant takes the brunt of the blue and uv exposure until the sun sets.


@CurrDogg420 forgot to mention the west facing bit is only due to your plant not getting a lot of the eastern morning sun. The eastern side can burn too once the uv and blue light stops filtering as the sun rises but since it isn’t getting that morning light from the east it’s getting all that high light blue and uv from mid day on. The only red and ir it’s really getting is the evening light.

You can move your plant to full light and put a small uv filter screen directly above it so that it gets the morning and evening sun but the mid day high light sun is diffused.

You’ll get more reds that way and less uv damage.


Thanks again @MDBuds , this is the sort of discussion I was hoping for.

I’m basically in the woods so my amount of morning and evening sun is sort of regulated by the distance to the tree line on either side. The middle of the veggie garden gets the best all-day sun but it’s occupied. I don’t really have many more great options in terms of location.

I’m actually not all that concerned about this particular plant. Her sisters crushed my 5x5. It was just sort of a light bulb moment for me, like “oh, yeah I guess I do get more evening exposure right here.”

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Sorry to hijack this thread. It seemed to flow along right into this. MDbuds, have you any thoughts on redshift trigger for deep sleep? There seems to be a plethora of material about it.

Dwight Butler Noddykitty


I have read many papers about plants and light outside. Not just cannabis. From my understanding the going theory is that when the sunsets you get the red shift. As the sunsets only the red wave lengths make thru as the sun is twilighting. The plants have many photo receptors that pick up on that red shifted light. And it’s signals to them to go into a deep sleep. And the theory is it turns off their other photo receptors.

Say versus indoor, where we just turn off the lights. They really don’t go to in a deep sleep the same way. It’s the main reason why the moonlight and street lights (city light pollution in general) doesn’t cause our outdoor girls to go hermaphrodite. Everything seems more sensitive to intersex traits with light leaks in doors. I don’t know this, I just found out an interesting read and theory. But lots of plant biologist feel this is the case.




Yeah that makes total sense and I’m seeing it too. I keep waiting for my southernmost girl to stop stretching cause she’s pushing 6’. Her sisters to the north have little baby buds.

I was just wondering about morning vs evening light too. My weed garden is closer to the eastern tree line than the veggie garden so it gets a lot more evening sun than morning. I wanted to get your thoughts about that.



So I’m doing some stoner napkin calculations here: her porch is a good 6’ from the ground…. :thinking: That changes the angle.

If my calculations are correct, I think that means I have to try growing a giant plant. :face_with_monocle: :yum:


Dwight Butler Noddykitty


My understanding is we get the same red shift in the morning sunrise as well as the evening sunset. I think it’s more important to have the high noon 6-8 hours than the evening or morning sun. It’s also why outdoor plants very often flower at 14 or 15 hours instead of just 12. Because that red shift in the last hour or two and the first hour or two acts like shaving off daylight. I have read about this a lot and it seems to play out in my garden. I have stuff that get the Eastern light, and I also have stuff that gets the western sunset light. And I don’t see a real big difference except individually north to south.

I wish I could use my big dog 🪚on my W neighbors cottonwood stand. I think he would notice.


I’m curious about what you said about street lights not effecting the plants. I’ve been keeping my girl inside at night because I have these two huge halogen lights that shine right in my back yard. I thought any light stringer than moonlight will cause stress on the plants?

@Noddykitty The reason moonlight and street lights don’t affect the plants usually is because the light source needs to be 50 ppfd or higher. That equates to 50 um per second or 50 micro moles per second. The moon light is only .01 um even during a full moon so it has no photosynthetic effect on plant growth.

Street lights also rarely reach high enough ppfd to affect plant growth unless you are growing your plant within 24 inches directly under the street lights as most are only 400 watt bulbs with reflectors at 90 degrees.

The reason light leaks indoor cause more issues isn’t because of the deep sleep or the red it’s because of the spectrum and intensity. An average led/cfl bulb in your home can put out 50 ppfd or more easily. Even those 13 watt cfl/led incandescent replacements. In order to avoid light leaks indoors you need to make sure all lighting is far enough away that it is under 50 ppfd at the tent. You can even go as far as to get diffusion screen for any lights near your grow area.

As far as the deep sleep theory regarding the red spectrum it is actually dependent on the ratio of red to far red usually express as r:fr in light studies. Far red does “put the plants to sleep” as some refer to it but really it just flips a genetic switch in the chlorophyll that turns on the genes that make the plant stretch for light like they do during the dark period anyway but while still using photosynthesis so the plant uses the sugars it is making instead of storing them.

If the far red (not ir) exceeds the red or deep red it tells the plant that night is coming or that it is in the shade and it will either make the plant stretch or shut off photosynthesis all together until the red and deep red exceed the far red and “wake the plant up.”

There are different ratios you can use indoors to accomplish different tasks but I would suggest not using a lot of far red. Red and deep red are great and work well with uv and ir to get plants to produce more trichomes and anthocyanins but if you use too much far red it will make your plants lanky and they won’t develop as many terpenes and anthocyanins as they should and it will also inhibit trichome production.

I myself don’t currently have the tools to measure light to do my own experiments to find the right ratios of far red to deep red but I do know for a fact that if you turn all lights off and use a far red bulb during dark time and then use a deep red/red bulb first thing at lights on and turn the far red off it increases the efficiency of photosynthesis during lights on.

I also know that during lights on you want a lot more red and deep red than far red. Ir is useful too at increasing the penetration of red and deep red to increase the efficiency of photosynthesis. If you don’t have the tools to figure out the ratio it’s best to just cut far red out all together during lights on. You can leave ir on 24/7 and it won’t really affect the plants without having the red on.

There’s a lot more to this and I can literally almost write a book on it, but instead I’ll hunt down a few of the studies I’ve read and post them here.

@Noddykitty @ChrisE @CurrDogg420 as far as the north to south discussion that all depends on the geological slope of your property. It doesn’t have much if any effect on a level plane.

This is because the sun doesn’t rise at exactly east. It’s more of a north eastern rise during spring and summer then after the summer solstice into the fall it moves to the south.

So if you are on a hill or a geological slope the southern side can be warmer and get more sun exposure where as the northern side will remain cooler and shadier until it starts getting the afternoon and evening light during the late summer and fall. That means the southern side gets light from dawn all the way until almost dusk but the northern side only gets light from high noon until dusk.

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