Inverse-Square 'LAW' of Light

[Philosophelon]

...a good approximation for the law of intensity fall-off is to find the cross sectional wavefront area and divide the emitted power by that.

Thanks! But what the hell does the "cross-sectional wavefront area" mean?
Is that the total surface area of the surfaces below the reflector on which light is shining?
Just the canopy dimensions 'cause the walls are reflective?

If we are referring to the intensity drop off -- then that is "the inverse square law in an isotropic case".

Do you know what they meant by an "isotropic" case?

Sorry about the jargon questions, but like I said, I got a C in physics, and that was probably generous.

 

[centralcoastbud]

Philosophelon - No idea man! The main response was everything minus the "the inverse square law in an isotropic case" part... that was from another guy but I didn't get a further response as I was staring at a packed bowl. Nice food-for-thought thread smokin.

 

[Philosophelon]

The main point is just dont say 25% anymore, its misleading....

Alright, you've convinced me. Which isn't easy, I think that's probably the first time I've ever posted that sentence on this board. K+

 

[swampy_nz]

I like just using the canopy area since its the only surface actually absorbing a large percentage of light. Also because the math for the surface area of just the canopy doesn't increase at all when you raise the lights. All you do is expose a litttle more of the reflective wall. I would just assume 90% reflectivity for most surfaces (besides plants/pots/soil) since most reflectors and mylar advertise 95%. I simply have faith that lets say 90% of the photons will be absorbed by the plant even when the light is twice as far away and that 3/4 of them will not just dissappear.

ok,that makes sense.In a completely enclosed space theoretically you could raise the light as high as you like and the canopy area will remain the same.all the light is still enclosed in the area,but the higher you raise the light the more reflective area is exposed,the more light is absorbed and so less light hits your canopy to be used.

 

[Weezard]

Da man thinks inside the box, yah?

Da man thinks inside the box, yah?

"BUT I still think I'm right... and I've never even stepped foot in a Physics class "

Obviously.:smile:

Fer instance
I still have no idea what you mean when you say "prism."

But, here's how practical guys figure this shit out.


Here's 2000 words for you.






Close enough for me, brah.
My reflective walls did not give lie to science.
Want I should do it again with the door closed?:wink:

Frankly, I expected more help from the reflection off the walls.


Disclaimer:
I'm not selling anything.
Could not care less what other folks illuminate with.
I use what I must, (LEDs), and they work jus; fine for me.

Regards,
Wee Zard

 

[charles_bronson]

not sure if anyone mentioned but if you put the light too close, your weed will be unpleasant no matter what law says what. im not sure how much room for argument there is on the law, but i don't think it applies to growing bomb as much as you guys would like to think. it really has almost nothing to do with it, as the temp of the bulb is MUCH more important than how many "lumens" your throwing at your canopy

 

[magiccannabus]

I have never seen a jihad of this magnitude upon any concept. I think you honestly may actually hate the inverse square law. Perhaps I am mistaken though. You really argue fiercely. If you want to understand how the inverse square law applies in an enclosed space, read up on optical focus, lensing, and fiber optics. Obviously if you just try to apply it as a direct rule to growing, what's the worst that will come of it? People will use more than enough light? In my opinion that's great, people should throw what they reasonably can at their plants. That's just being a good parent....

 

[magiccannabus]

I'm sorry, but I have really said what I think I need to. I'm not sure what else to tell you really. You've browbeat me into submission. We're not even disagreeing in a sense, but we obviously think the other can't see reason. I'm gonna just leave it at that, hope things go well for you.

 

[swampy_nz]

 

[TheMintMan]

"BUT I still think I'm right... and I've never even stepped foot in a Physics class "

Obviously.:smile:

Fer instance
I still have no idea what you mean when you say "prism."

But, here's how practical guys figure this shit out.


Here's 2000 words for you.


View attachment 11355

View attachment 11356

Close enough for me, brah.
My reflective walls did not give lie to science.
Want I should do it again with the door closed?:wink:

Frankly, I expected more help from the reflection off the walls.


Disclaimer:
I'm not selling anything.
Could not care less what other folks illuminate with.
I use what I must, (LEDs), and they work jus; fine for me.

Regards,
Wee Zard

 

[TheMintMan]

Nice Job, so how long has everyone been spreading this terrible advice!

Probably about as long as they've been growing the dank, with said advice.

I think it goes without saying that most graphs and charts are just general guidelines to let the noobs know where your safe ranges are. That's why I like when people like Weezard actually have the equipment to prove what they're saying before getting all belligerent about a minute point. You know what they say...when arguing takes over growing as your main forte...smoke a joint and mellow out...or something like that.

Let it go b...let it go.

You're right...happy? :smile:

 

[Lt. Herb]

Wow dude.

Inverse square law does not apply to indoor growing at all. I think this is the point you're trying to make, right? Well you're wrong. Dress it up how you like, it applies. There are other factors to be accounted for, but it still applies, and to a greater degree than you will ever admit.

For one, you are assuming way, way to much reflection from your walls/refelctor. I know from experience that scientific grade reflective optics (mirrors, gratings, ect.) STRUGGLE to achieve 90% reflectivity, so there is no way in hell you achieve 90% in a grow room ever (even with mylar that says 99.9% reflectivity, maybe in a lab somewhere, but not in practice). At best I would assume 75-80% reflectivity to be about the max you could achieve. Even at 80%, once the light strikes 6 surfaces its has lost 73.7856% of its energy, regardless of how far it travelled. So, the only light you can really count on is the light coming almost directly from the bulb itself, as any photons that take the scenic route aint doin' shit for photosynthesis.

This is why people use the ISL, because all the uber light you're counting on from your reflectivity is not so uber. In the end the majority of the useful light is coming directly from your bulb, which is where the ISL comes into play. It's not exact, but it's a pretty good approximation, and a damn sight closer than the horseshit you been spoutin'.

 

[TheMintMan]

If you don't think his test was accurate...get your own equipment and do your own. I would, but I don't care enough. I'm here to grow good weed, and help others do the same. So far, that's been going swimmingly. Why are you here?

Oh that's right...you want people to "stop saying that the light intensity will be 25%...". Good luck with that. I don't use that chart or any chart because I can read my plants fairly well thesedays, but I can tell you that it's not "way off" due to several successful grows within the range that the chart suggests.

 

[pinecone]

When you realize how right I actually am, I expect something like

You seem to be on a mission to convince everyone your right, rather than to discover the truth.

Weezard actually presented compelling empirical evidence that the inverse-square law is applicable to his indoor growing environment. If you want people to buy your argument you have to provide some evidence. Pull all the plants out of your cab, get a light meter, and start taking some readings - or find someone that will do it for you.

Pine

 

[T.J]

But ofcourse it wasn't accurate !!

Open door, side lighting, plants and other obstructions. Come on, thats no way near a point source in "space". Look at this picture again;

http://icmag.com/ic/picture.php?albumid=3550&pictureid=82084

There you clearly see everything that smokinshogun is saying. His point is well proven now, both by real physicians and logical thinking.

It's always like this when old things get challenged. Lumen ain't got nothing to do with growing either, but that can be a different crusade

 

[TheMintMan]

The optimum zone on that chart goes goes from 100% intensity ALL THE WAY to only 8% of that. I replace my bulbs at 80% light loss, so couldnt I just lower my light to make up for that light loss?

The 'law' DOESN'T apply because you can use that whole optimum zone and still get dank plants, so you're almost right...

But you'll get better results the closer you get to the light...to an extent. It's about reading your plants. The range may be wide, but like I said, for people who have ZERO idea where to start...it works. Start at the bottom..start moving them up until you have problems then back them down a bit and there it is. It's like tuning a guitar.

I'll take your word for it when you start showing me some of your uber grows. Or at least when you've done a test, with appropriate equipment. I know what you're saying, but you made your point and others have made theirs and they don't mesh up. The problem is your arguing about two different things.

Whoever has the best weed is right.

i know I'm right, it doesn't really matter if you all are wrong, I could really care less what you believe.

Boy for someone who could care less...you sure have gotten yourself worked up over this. I'm pretty sure I know what the problem is...look...repeat after me.....

 

[T.J]

Why does he need to show super grows to be right?

If physicians say it doesn't apply, then is doesn't apply! Simple as that.

And I think he is fed up with people not reading his posts.. If you would, you would see his point quite clearly the right one.

 

[niacinamide]

I have never seen a jihad of this magnitude upon any concept. I think you honestly may actually hate the inverse square law.

You may want to check out timecube.com if you haven't already. It's a trip.

ITS ALL ABOUT SURFACE AREA, and even then we have a thing called reflection.

I understand what you are trying to say. You are thinking of a light source as like a shower head in a box with all the water bouncing off the sides of an enclosed area and pooling at the bottom.

Yet even using mylar and other highly reflective surfaces in dealing with light, there is still going to be a certain amount of loss. Now does that loss follow the inverse square law exactly? Of course not. The inverse square law nonetheless can serve as a quick "rule of thumb" that people can use to reach a rough estimate. At the very worst, you end up with more light than you had hoped for due to reflectivity. Not such a bad outcome after all.

Wouldn't you agree that the larger the enclosed area, the more the accurate the inverse square law becomes? If so, going in opposite direction then with progressively smaller areas, exactly at what point do we ignore its estimates?

 

[TheMintMan]

Why does he need to show super grows to be right?

If physicians say it doesn't apply, then is doesn't apply! Simple as that.

To me, seeing is believing. Just like in any other job...some people know their shit, others are just spouting off shit. The fact that someone's job title is "physician" doesn't mean their argument is the end all. Waaaay too often do I hear people with no actual knowledge of their own quoting the ONE doctor that they go to regarding marijuana...and usually, the doc doesn't know what he's talking about. But aren't doctors always right? No, absolutely not.

He doesn't need to show any uber grows to be right. That's just what it's going to take for me to believe that he knows from experience what he speaks of...and didn't just read an article or a chart (which would be kind of ironic wouldn't it?) and take their word for it.

 

[pinecone]

Yet even using mylar and other highly reflective surfaces in dealing with light, there is still going to be a certain amount of loss. Now does that loss follow the inverse square law exactly? Of course not.

This is where I am. The remaining question from my perspective is "how bad of an approximation is it." I'm leaning toward, "not bad at all" in a typical indoor environment, but I could be convinced otherwise by some solid empirical evidence. Theory just doesn't cut it as we are dealing with irregular areas and surfaces that make the application of theory far too complex.

Pine