Mirror Room...

[DJ GreenThumb]

yes, the fact that people keep saying glass absorbs light is "basically" a myth. It absorbs the deep ultra violet spectrum, but not visible light or any light that is good for plants. I am not sure where you get that 10 or 20% figure you state, but it's not true. Pure glass does not absorb any of the visible spectrum.

http://www.wonderquest.com/why-glass-is-transparent.htm

I can't find any of the old references I once found when researching this subject, but common household mirrors have reflectivity of well over 99%. The light passing thru the glass is not a factor to worry about unless it's tinted, in which case it's the tinting that blocks the light and not the glass.

From your reference:

"Glass is almost perfectly opaque to deep ultraviolet, which is why it's hard to get a tan through a window," emails physicist Louis A. Bloomfield of the University of Virginia. "By deep ultraviolet, I mean UVB and UVC."

UVB is good for cannabis....well maybe not good for it but its good for what we want. UVB increases trichome production as a defense mechanism to UVB. So I would not want any reflective material in my grow room that cuts out UVB

 

[NLXSK1]

glass gets warm because it's absorbing the ultraviolet, not the visible spectrum. the amount of visible light absorbed by glass is negligible. Decent glass absorbs no more than .5% of visible light per 10mm. That is practically nothing, and it is science based.

You just agreed with me. .5% > 0

Why would you use a material that removes ANY part of the reflected light when you can use a cheaper material that is more effective?

 

[Kerovan]

You just agreed with me. .5% > 0

Why would you use a material that removes ANY part of the reflected light when you can use a cheaper material that is more effective?

It is still more reflective than all of these other surfaces that are used to reflect light. Mirrors still reflect more than 99% of light. That is more than the 95% for good mylar which is the best commonly used material.

 

[TaoWolf]

It is still more reflective than all of these other surfaces that are used to reflect light. Mirrors still reflect more than 99% of light. That is more than the 95% for good mylar which is the best commonly used material.

See this is what I don't get about what you are saying... You are saying mirrors reflect more than 99% of light... as if all mirrors are even made of the same 'mirror' material. And considering that most mirrors use a polished aluminum backing behind panes of glass, and that polished aluminum is only about 95% reflective and the glass coverings absorb some amount of light... how do you arrive at 99+% for any mirror? Or what kind of mirror are you talking about??

Mylar is just a plastic sheet that can have a reflective coating of aluminum applied to it... the same aluminum in most mirrors that has about 95% reflectivity (it just doesn't suffer from a loss of light to a glass covering like aluminum mirrors do)...

So how do you arrive at a 99+% reflectivity which is even higher than the reflective material used in mirrors?

 

[Brick Top]

Originally Posted by Brick Top Mirrors are horrible for use as a reflective material for growing. Mirrors are of course very reflective but they only reflect a specular reflection. Specular reflection is a direct reflection, light strikes the mirror and is reflected at the exact angle the light strikes the mirror. That does not give an even, spread out reflection of light. You end up with only parallel rays of reflected light


Diffuse reflection is what is best for a reflective material for growing. A textured or rough surface, even just a microscopically rough surface, when struck by light rays will reflect them in many different directions so there is a much broader and much more even coverage of reflected light.

that's not the point that I am arguing. I am trying to dispel the myth that the glass used in mirrors absorbs light, which it doesn't.

Regardless of that being a fact or not a fact, the fact is mirrors are a terrible choice for a reflective surface or material for a grow room. No matter how much light they reflect or no matter how much light they do not reflect is meaningless in a discussion about if are mirrors a good choice for reflective surfaces/materials for growing.

People focus too much on percentage of reflectivity and not enough on what type of reflecting happens.

Specular reflection is unwanted, it is a poor type of reflection for growing. Diffuse reflection is wanted, it is a perfect type of reflection for growing ... so and and all other information about mirrors is immaterial in relation to using them for reflective surfaces/materials for growing. It does not pertain in any way about the usefulness of mirrors for a reflective surface/material for growing. It is totally extraneous information in regards to the question of; "Are there reasons why you should not use mirrored walls and floor?" which is exactly what this thread is all about. It is not at all about do mirrors absorb any percentage of light or not.

Accurate topical information is important and is what was asked for and what is needed. Off topic completely extraneous information was not asked for and it is unneeded and does nothing to answer the question the thread started asked.

What you are arguing and attempting to dispel is a topic for a completely different thread. Possibly you may care to begin one and see who really cares since mirrors have long been known to be a terrible choice for a reflective surface/material for growing and growing is what this site is all about and not about if mirrors absorb any amount of light or not.

 

[Brick Top]

It is still more reflective than all of these other surfaces that are used to reflect light. Mirrors still reflect more than 99% of light. That is more than the 95% for good mylar which is the best commonly used material.

Percentage of reflectivity is not as important when it comes to a reflective material as how light is reflected. Specular reflection is poor reflection regardless of what percentage of light is being reflected. Diffuse reflection is good reflection even if it reflects a lower percentage of light is reflected than a specular reflection might reflect because it is a broad spread out and even type of reflection.

Since the thread is about are mirrors a good reflective material for growing, and not are they more reflective than Mylar or other reflective materials, your argument is immaterial and completely off topic.

 

[stickybob]

stick to diamond grade reflectice sheeting at the end of the day

 

[Windex]

Glass will fuck up your grow. Just compare a 600w grow with a normal reflector and a 600w grow with a cooltube.

 

[SCARHOLE]

Im not a physics teacher or anyting, but Mirror is way more reflective than white.

If i flashed you driving with a piece of mirror you would be blinded cause its reflecting back over 80% of the light.
If i flashed you with a piece of white wood, nothing.

Ive never believed white is more reflective than mirrors.
Im using mirrors im my grow box now , it eliminates the need for side lighting an it apppears way brighter in there.
Its never gave me any problems.
My whole cab is a polished reflector.

 

[lime73]

plants don't see the way we do??? so a comparison vs human eyes is out! imo

what is all the fuss about? mirrors break....not a good thing!!! save the mirrors for the bedroom...not the growroom! lmao just a thought

 

[Brick Top]

Im not a physics teacher or anyting, but Mirror is way more reflective than white.

If i flashed you driving with a piece of mirror you would be blinded cause its reflecting back about 80% of the light.
If i flashed you with a piece of white wood, nothing.

Ive never believed white is more reflective than mirrors.
Im using mirrors im my grow box now , it eliminates the need for side lighting an it apppears way brighter in there.
Its never gave me any problems.

View attachment 1269247

Just one more time .... mirrors reflect a specular reflection and surfaces like Mylar and flat white paint, etc, reflect a diffuse reflection. Mirrors do reflect a higher percentage of light that strikes them than those other types of reflective materials but they do not reflect it in a way that is as even and as useful for plants to use for growing. Percentage of reflectivity is not everything, it is not all important when it comes to reflectivity in relation to plants light needs and growing.

Consider this example.

You are in a pitch black room with one mirror on one wall and you have a flashlight that projects a narrow beam of light. You shine the flashlight at an angle at the mirror. What does the light do, how much of the room is lit up by the one narrow beam of light? The beam of light is not seen, or hardly seen until it strikes the mirror and again not until it strikes the wall following the angle the light beam was aimed/pointed at the mirror. The light beam is tightly/narrowly directed due to the specular reflection of the mirror.

Now do the same in a pitch black room without any mirrors but the walls are painted flat white. The light reflects over much more of the room, lighting up much more of the room.

Why? Because mirrors have a specular reflection, a highly directional reflection and a textured surface, such as flat white paint, has a diffuse reflection that redirects the light rays in many different directions at the same time regardless of what direction the light rays initially came from.

Does that help to explain why materials like Mylar and Foylon and flat white paint and titanium white paint and white plastic that is sometimes called panda-poly or panda plastic or just poly are better reflective materials for growing plants than mirrors?

Regardless of what angle light rays strike any area of those types of reflective materials they reflect the light rays in all different directions at the same time and mirrors only reflect light rays at the angle in which the light rays strike the mirror rather than reflecting the light rays in all different directions at the same time.

Is all that just too simple for some people to be able to comprehend? Are the minds of some members here too highly trained to be able to understand such a simple concept?

 

[SCARHOLE]

Agreed, but the light is reflected an foccuses toward the bottom of my ladies where they dont get much light. (took forever to get the angle right)
specular reflection is diffused an very week compared to mirrors.

The main disadvatage to mirrors is it breaks. But i do glass for a living an it can be done safely.
For saftey I used 1/4 inch thick, saftey backed mirror clear siliconed to the walls. (ONY USE CLEAR, others eat the crome an copper plating off the back of mirrors.)
An my price was free, witch is cheeper tham mylar an panda.

 

[Brick Top]

specular reflection is diffused an very week compared to mirrors.

As the original Maxwell Smart, Agent 86, used to say after being told long directions; "you lost me at the bakery" with that one. Specular reflection is how mirrors reflect, they do not have a diffuse reflection so unless my wake and bake really did me in I just don't understand what you meant when you said; "specular reflection is diffused an very week compared to mirrors."

That is an example of specular reflection, that is how mirrors reflect a single ray of light. Whatever angle light strikes a mirror it is reflected at the exact same angle. Add multiple rays of light and you have the exact same thing, just with more rays of light running parallel to each other, all coming off the mirror at the same angle they struck the mirror.
It is not a diffuse reflection.

This is diffuse reflection. The blue lines are light rays striking the reflective surface and the red and black lines are the reflected light rays. Even though all light rays come in at the same angle the light rays are reflected in all different directions and they are reflected at differing angles. That is diffuse reflection. The reflected light rays are split up and reflected in different directions. They cover more area, a wider broader area, they reflect light to places specular reflection cannot reflect it.

It is the same basic principal behind the higher dollar and higher quality dimpled/textured reflective light hoods. The light rays coming from a bulb are reflected in a diffuse manner, reflecting in far more different directions giving a wider broader more even distribution of reflected light than what comes from a smooth surface that only provides a specular reflection.

An my price was free, witch is cheeper tham mylar an panda.

That goes a long way to explain why you use mirrors. To many people if something is free or even just very inexpensive regardless of how poor of an option it is to use, it because impossible for them to resist using it, when to instead use something good to very good to great would mean they would have to pay a little to a bit to a lot.

The friend I have known longest in life, roughly 47 years now, is a carpenter and he gets his hands on all sorts of things for free ... and he finds some way to use almost all of it ... and regardless of how impractical something may be to use the way he ends up using it or how poorly it does the job he uses it for, because it was free he will still use it. Then, what I consider too be the amusing part of it all, he then convinces himself, and then tells others, that it is the greatest thing since sliced bread and works better than that stuff I, or someone else, paid for.

 

[Kerovan]

Since the thread is about are mirrors a good reflective material for growing, and not are they more reflective than Mylar or other reflective materials, your argument is immaterial and completely off topic.

no, my argument is not off topic. I am not saying mirrors are "the best" surface for a growroom. I don't know that for a certainty since I never tried it. I am just trying to counter the bullshit myth that mirrors are less reflective than these other surfaces because glass absorbs too much light. Mirrors are the best reflective surfaces you can get, period.

 

[Brick Top]

no, my argument is not off topic. I am not saying mirrors are "the best" surface for a growroom. I don't know that for a certainty since I never tried it. I am just trying to counter the bullshit myth that mirrors are less reflective than these other surfaces because glass absorbs too much light. Mirrors are the best reflective surfaces you can get, period.

The question asked was; "Are there reasons why you should not use mirrored walls and floor?" What you have been discussing in no way addresses or answers that question. Just because someone else went off topic and wrongly said glass itself absorbs some amount of light, refuting them does not mean you remained topical to the thread starters question.

But since you mentioned light absorption, again, did you happen to read the bit of the article I PM'd you from M.I.T. that said the metallic backing of mirrors does absorb a small percentage of light rays?

So when someone blames the light absorption of mirrors on the glass itself they are incorrect as to what they blame the absorbtion on, but as the researchers at M.I.T. did clearly state, mirrors do absorb some amount of light rays due to the metallic backing.

 

[Kerovan]

The question asked was; "Are there reasons why you should not use mirrored walls and floor?" What you have been discussing in no way addresses or answers that question. Just because someone else went off topic and wrongly said glass itself absorbs some amount of light, refuting them does not mean you remained topical to the thread starters question.

On that point, yes you are correct. It wasn't directly related to what the original poster asked.

But since you mentioned light absorption, again, did you happen to read the bit of the article I PM'd you from M.I.T. that said the metallic backing of mirrors does absorb a small percentage of light rays?

no I did not read that article. I never got any PM from you..

 

[TaoWolf]

The question asked was; "Are there reasons why you should not use mirrored walls and floor?" What you have been discussing in no way addresses or answers that question. Just because someone else went off topic and wrongly said glass itself absorbs some amount of light, refuting them does not mean you remained topical to the thread starters question.

But since you mentioned light absorption, again, did you happen to read the bit of the article I PM'd you from M.I.T. that said the metallic backing of mirrors does absorb a small percentage of light rays?

So when someone blames the light absorption of mirrors on the glass itself they are incorrect as to what they blame the absorbtion on, but as the researchers at M.I.T. did clearly state, mirrors do absorb some amount of light rays due to the metallic backing.

Again, you guys are talking about theoretical mirrors and all these properties without even defining the kind of reflective material being used in whatever kind of mirror you are claiming have very specific properties (which is nonsensical) . All the the while saying established, quantifiable, and provable mathematics and physics, that has been known to mankind for over three centuries, is irrelevant in regards to the ONLY aspect of mirrors that is universal and defined by people in this discussion: the glass panes that cover whatever reflective material is used and what effect that glass has on things.

And of course the metallic backing of mirrors absorbs a small percentage of light. How is that material different (or less efficient) at reflecting light when behind panes of glass as opposed to when *not* behind panes of glass is the very discussion.

To say it is wrong that glass absorbs light is completely counter to established physics. Beer-Lambert. Look it up. Even the air light travels through absorbs light to a noticeable extent - let alone solids like glass. It's the very reason our sky changes colors and we don't all explode into ashy lumps courtesy of the sun. The reason you can't get a sunburn sitting inside behind a window. The reason that jaundice can be treated by going outside and not by sitting under a skylight... etc...

 

[Marthacrookshanks]

Wow, I can't believe grown adults are having this discussion. The true mirrors that reflect the highest volume of light waves visible and non visible have no glass others are coated in quarts, same for lenses that look into space. Any mirror with glass in is only a cheap alternative good for looking at yourself, and people in cas behind you in.
There is a lot of physics involved in explaining why, and unless you have a grasp of it your not going to understand that glass mirrors are not as reflective as you Kerovan are making out. And Certainly not good for using as a growing reflector, which is what the original context the question was asked in.
But the very best reason not to use mirrors in a grow room that no one seems to be saying here is cost. Mirrors v.s Mylar Or Black white sheet is gonna a big difference, and would not do as good a job as mylar or white black sheeting. for the fact that all reflections from a mirror are specular and for it to have an even coverage the light or the plants would have to be constantly moving. This is why its best to use the products that are out there for applying to surfaces in grow rooms.

 

[Brick Top]

no I did not read that article. I never got any PM from you..

I will resend it.

 

[Brick Top]

Originally Posted by Kerovan
no I did not read that article. I never got any PM from you.

I will resend it.

In case it fails to reach your PM box, a second time, here is the portion of the article from M.I.T. that I have now sent twice.

M.I.T. on mirrors ....

Mirrors come in two basic varieties. The most common are metallic mirrors like those found on the walls of Versailles or on medicine cabinets. Metallic mirrors work pretty well, but they have limitations. The most important is that they waste energy, absorbing a small fraction of the light that falls on them. That is because when light, which, like radio waves, is a form of electromagnetic radiation, strikes a metallic mirror the electrons in the metal move just as they do when a radio signal strikes an antenna. Pushing electrons around takes energy, which dims the reflected image. ​

You have been correct that it is not the glass itself that absorbs light rays/energy. It is instead the metallic backing behind/under the glass that absorbs a small percentage of light rays.

Light absorption does take place but most people wrongly blame it on the glass itself rather than the metallic backing beneath/behind the glass.