Mirror Room...

[ILikeWhatYouGot]

Hi All. First post today. First question..


Are there reasons why you should not use mirrored walls and floor?


Thanks for looking.

 

[TaoWolf]

Mirrors have glass over the reflective surface which absorbs light (and the glass absorbs light both ways when being reflected) - better to just use a reflective surface sans glass.

 

[lime73]

Hi All. First post today. First question..


Are there reasons why you should not use mirrored walls and floor?




Thanks for looking.

Well safety would be a good one....mirror break and if it is in your garden??? I would not want to clean it up!!!
And mirrors are not as reflective as they seem to us, the plant uses light and if the glass is absorbing some of the light it is almost useless...there are better reflective surfaces than mirrors! And Safer too....just a though?

 

[ILikeWhatYouGot]

lol ok. maybe didn't really think that one through. Thanks Guys

 

[Kerovan]

broken glass is the only worry. Regardless of the MYTHS going around, mirrors are the absolute best reflective surface you can get. They do not absorb light, that is an old wives tale that people keep repeating that is 100% false.

 

[wannaquickee]

hot spots...........

 

[TaoWolf]

broken glass is the only worry. Regardless of the MYTHS going around, mirrors are the absolute best reflective surface you can get. They do not absorb light, that is an old wives tale that people keep repeating that is 100% false.

How can you say mirrors are the absolute best reflective surface when different mirrors use different reflective surfaces? Most mirrors in a home will just have a polished aluminum sheet behind some glass - but an aluminum mirror simply won't reflect as much light as a straight polished aluminum sheet without the glass absorbing some light. Other mirrors use different reflective surfaces so their reflective qualities are going to be different based on that alone (minus the light lost to the glass coverings).

It's no myth, glass just absorbs a little light and provides no benefit for a reflective surface - unlike with sealed reflectors which trade a little loss in light in order to lower radiant heat.

 

[Kerovan]

How can you say mirrors are the absolute best reflective surface when different mirrors use different reflective surfaces? Most mirrors in a home will just have a polished aluminum sheet behind some glass - but an aluminum mirror simply won't reflect as much light as a straight polished aluminum sheet without the glass absorbing some light. Other mirrors use different reflective surfaces so their reflective qualities are going to be different based on that alone (minus the light lost to the glass coverings).

It's no myth, glass just absorbs a little light and provides no benefit for a reflective surface - unlike with sealed reflectors which trade a little loss in light in order to lower radiant heat.

I can say that because it's the truth. If you don't like it, that's not my problem. I am just countering a common myth with a little reality. Not everybody will believe it though, just like you don't believe it. That is how the myth keeps going. The amount of light absorbed by the glass is completely negligible....

 

[TaoWolf]

It's not a matter of liking or not liking - was *simply* hoping for an explanation. I'm open-minded enough to listen if you care to elaborate at all.

And what myth? That glass absorbs some light?

------------

Alright well just in case anyone is interested in mythology - good quality clear glass like that used in windows and mirrors has a Visible Light Transmittance (VLT) of around 90% (a 10% loss of visible spectrum light just from traveling through the glass once) according to most manufacturers of glass. Around 100% of UV radiation is absorbed. With mirrors, the light travels through the glass twice (once upon entering and once upon leaving) so the loss can be up to 20% with one reflection. Light loss is even higher if the light is entering the glass at an angle as it has to travel further distances or being reflected back and forth through multiple glass panels. Additionally VLT drops dramatically once/if the glass gets dusty or dirty at all.

So if one considers 100% UV loss and a minimal 20% loss in visible light under perfect conditions completely negligible - no worries. We just have different viewpoints.

 

[budlover13]

Ok. Here's my two cents. The theory behind mirrors reflecting light makes sense at first until you start reading up on light loss through glass. I know I asked the question when I first started. I would venture to guess that a mirror CAN be more reflective than Mylar, but not the mirrors people commonly think of. I'm thinking more like the mirrors used in deep space telescopes and the like. That being the case, it would obviously be cost prohibitive. I'm no scientist or expert on light behavior, but I do have a basic idea, I think. I use mylar in my flower closet and my veg box, I figure it's worked for a lot of people and I still have a LOT to learn about Mary. I'll focus my efforts in other areas that I think can and do make a bigger difference than your reflective material.

 

[Kerovan]

And what myth? That glass absorbs some light?

------------

Alright well just in case anyone is interested in mythology - good quality clear glass like that used in windows and mirrors has a Visible Light Transmittance (VLT) of around 90% (a 10% loss of visible spectrum light just from traveling through the glass once) according to most manufacturers of glass. Around 100% of UV radiation is absorbed. With mirrors, the light travels through the glass twice (once upon entering and once upon leaving) so the loss can be up to 20% with one reflection. Light loss is even higher if the light is entering the glass at an angle as it has to travel further distances or being reflected back and forth through multiple glass panels. Additionally VLT drops dramatically once/if the glass gets dusty or dirty at all.

So if one considers 100% UV loss and a minimal 20% loss in visible light under perfect conditions completely negligible - no worries. We just have different viewpoints.

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.

 

[cadeneli]

Using mirrors for growing is not any different than painting your walls black. Especially in a mirrored room.

 

[TaoWolf]

Ok, you are right and Beer, Lambert, and Bouguer were all wrong and it's basically a myth. You win. The aluminum behind the glass in most mirrors doesn't even attain 99% reflectivity.

 

[Leothwyn]

I suppose glass may absorb some of the light that passes through it... I don't how much. But, considering how well my houseplants thrive sitting next to a window, I'd have to assume that a useful amount of light is getting through. I expect that there are surfaces that reflect better, but to say that mirrors are totally worthless, or the same as painting your walls black just doesn't sound right to me... sounds like hyperbole. I'm no expert, just going on my own common sense (and observations w/ houseplants).

 

[NLXSK1]

Kerovan,

Look at this at a more basic scientific level.

Light is an emission of photons in various wavelengths from a source. These photons speed away from their source until they come into contact with something.

Now, glass is composed of primarily silica. This silica is not completely transparent, it just appears so to our eyes. When you look at glass on the microscopic level you can see the structure.

Ok, so the photons travelling from the source are going to hit the glass. And some of them are going to come into contact with the silica structure of the glass. This results in the transfer of energy into heat which causes the glass to get warmer. Dont believe me? Touch the glass of a grow light. It is hot because some of the photons passing through it are converted to heat energy when they come into contact with the glass structure.

Now, I can guarantee you that glass is denser than the atmosphere under normal conditions. Therefore, to some degree or another, a mirror will reduce the amount of light reflected back toward the source. It is not a myth, it is simply science.

 

[NLXSK1]

Mirrors will work. However, as most people are pointing out, you can get better reflectivity at a lesser cost by using other methods.

 

[Brick Top]

Regardless of the MYTHS going around, mirrors are the absolute best reflective surface you can get.

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.

 

[Kerovan]

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.

 

[Kerovan]

Kerovan,

Look at this at a more basic scientific level.

Light is an emission of photons in various wavelengths from a source. These photons speed away from their source until they come into contact with something.

Now, glass is composed of primarily silica. This silica is not completely transparent, it just appears so to our eyes. When you look at glass on the microscopic level you can see the structure.

Ok, so the photons travelling from the source are going to hit the glass. And some of them are going to come into contact with the silica structure of the glass. This results in the transfer of energy into heat which causes the glass to get warmer. Dont believe me? Touch the glass of a grow light. It is hot because some of the photons passing through it are converted to heat energy when they come into contact with the glass structure.

Now, I can guarantee you that glass is denser than the atmosphere under normal conditions. Therefore, to some degree or another, a mirror will reduce the amount of light reflected back toward the source. It is not a myth, it is simply science.

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.

 

[Kerovan]

Ok, you are right and Beer, Lambert, and Bouguer were all wrong and it's basically a myth. You win. The aluminum behind the glass in most mirrors doesn't even attain 99% reflectivity.

and where do these people that lived in the 18th and 19th century prove that glass absorbs 20% of light?