The Mirror Enigma

I have a personality where I must scrutinize everything and understand exactly why something is the way it is. I have an issue with the list of reflective surfaces being used by growers. Reason being is everyone assumes mirrors absorb light, create hotspots, or don't reflect usable light for the plants. All of which makes no sense and here is why:

1) Mirrors absorb light
My problem with this is that when I test a mirrors reflectivity vs a piece of poster board I painted flat white or even Mylar the mirror wins by a noticeable amount. If that saying was really true then how the hell would you be able to see a reflection if a mirror absorbed light? That goes against the enitre point of a mirror.

2) Hot spots
This makes sense but I actually noticed my room get cooler after I installed mirrors on every surface (my grow box is almost 100% mirrored surfaces) Also my 42w CFL's are literally 2"inches away from the plants so I'm not exactly concerned the reflection may create the same amount of heat. Hell it may even mean its as if I have double the lights! Dunno about that yet but I will do further testing.

3) Mirrors don't reflect light that is usable to plants.
Strange as mirrors can reflect not only all visible light but 99.9% of ALL light spectrums. This includes ultraviolet and even microwaves. S they certainly reflect

Now I know in the Cannabis bible it has a chart with Foylon at the top followed by poly and Mylar but there is no mention of mirrors except for a prewritten response saying the above mentioned "facts". What I want to know is who wrote that and what tests did they use because I am seeing the exact opposite.

**Please only comment if you have something useful to say. I dont want to see 30 replies with "dude mirrors absorb light everyone knows that!" If you are going to respond you must explain yourself and where you got this information and it must be a verifiable and repeatable statement. My ultimate goal for this is to gain a better understanding as to why exactly those other products are used when again mirrors have produced more light than anything I have used (couldn't afford Foylon to test with to be fair)

awesome question! way to call it out, I honestly dont have the answer to your question but ill be watching this thread for it

The reason mirrors absorb light is that it has to travel through a sheet of glass, hit the reflective surface, then travel again through the glass as it is bounced back. This cuts down light intensity by a percentage.

Nocturn3 said:

The reason mirrors absorb light is that it has to travel through a sheet of glass, hit the reflective surface, then travel again through the glass as it is bounced back. This cuts down light intensity by a percentage.

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absolutely the mirror will cut down on some light but still as far as I can tell it is more reflective than either mylar or flat white paint. thanks for replying but you offered no legit answer to the question I posed.

The biggest factor I see more than anything is weight and positioning. Mirrors may be practical and easily mounted in a small area, but in a larger area it's an extra layer for something to get under and contaminate. I wouldn't be stoked having to dismount and remount panels in between grows to make sure things are as clean as possible.

Compared to potential maintenance, it's the easiest to scrub a brightly painted white wall, and it's easier to take down mylar/panda wrap and scrub between grows and hanging new wrap. Those are the two main factors. The only other factor that I can see is that glass also has an ability to retain heat, so higher powered HID lighting could potentially generate a hot spot on an area of glass. The reflective material on the glass also has some metallic properties and will retain a small amount of heat. If you are using CFLs, they don't generate as much as a 1000w MH bulb will.

Good rule of thumb would be to keep trying to smoke a flame through a glass pipe. Eventually it will be too hot to the touch and will need time to cool down. It's the same principle with mirrors. Most pipes I use are blown with tempered glass too. Another thing to consider.

this is great info because i was just wondering as i was painting my grow room white (painting sucks d***) why cant i just line the walls with mirrors?!

Because mirrors dont disperse the light in all directions, they pin point the light

saycheese said:

1) Mirrors absorb light
My problem ...

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Mirrors reflect coherent images, but this is completely seperate from if they reflect more or less light. In general white plastic reflects more light than a mirror, but you cannot focus that light to a small area to test that.

saycheese said:

2) Hot spots
This makes ...

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If they are in a closed space, the light is spread out randomly by white materials, but it is coherently reflected by a mirror. Hot spots do not exist for cfls because they are not hot enough until you get a really lot of them. Any grow needs to be around 1000wats, hid or if possible cfl, in order to experience the true force of hot spots. The infrared is coherently reflected by the mirror too, and you can basically point heat rays into a small area and cook your plants. This happens with tinfoil reflectors, and could easily happen when mixing mirrors and hids.

saycheese said:

3) Mirrors don't reflect light that is usable to plants.
Strange ...

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Dont know the details, but you would have to know the exact wavelengths the plant is using (like the LED growers are trying to do) and measure the reflectivity at that wavelength, that is the true measure. It is impossible to do yourself, and my guess is that a trusted reflective material is going to reflect that wavelength better than a typical mirror.


Mirrors are designed so you can see perfect reflections, not so that those reflections are as bright as possible.

thesmokering said:

Mirrors reflect coherent images, but this is completely seperate from if they reflect more or less light. In general white plastic reflects more light than a mirror, but you cannot focus that light to a small area to test that.




If they are in a closed space, the light is spread out randomly by white materials, but it is coherently reflected by a mirror. Hot spots do not exist for cfls because they are not hot enough until you get a really lot of them. Any grow needs to be around 1000wats, hid or if possible cfl, in order to experience the true force of hot spots. The infrared is coherently reflected by the mirror too, and you can basically point heat rays into a small area and cook your plants. This happens with tinfoil reflectors, and could easily happen when mixing mirrors and hids.



Dont know the details, but you would have to know the exact wavelengths the plant is using (like the LED growers are trying to do) and measure the reflectivity at that wavelength, that is the true measure. It is impossible to do yourself, and my guess is that a trusted reflective material is going to reflect that wavelength better than a typical mirror.


Mirrors are designed so you can see perfect reflections, not so that those reflections are as bright as possible.

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1)"Mirrors reflect coherent images, but this is completely seperate from if they reflect more or less light"
IMAGES ARE LIGHT!!!!!! This makes no sense.
2)Hot spots not only means temperature but a specific point of greater light intensity.
3)Wavelength impossible to measure?
I think not. Just an expensive device. They run about $250-$300. I can't afford one, can you?

Unfortunately you replied with complete opinion which is exactly what I didn't ask for. None of your information had any scientific or statistical data to back up plus you separated images from being light which is just pure ignorance. Hate to sound so hypercritical but I am finding info on these forums to be of utterly useless as no one is willing to spend the money to buy the equipment to find out real answers. I don't have the budget for a wavelength meter but I'm hoping one of you would seeing as how this would be in the best interest of a professional grower.

you have to understand most of the information on these forums is just info rehashed from the growers bible, or info traveling by word of mouth. take everything you hear with a grain of salt.

and im willing to bet there are very few professional growers here. (true professionals would want to hide their identity as much as possible)
and differences in reflective surfaces between mirrors/white paint/mylar...how much of a difference does it make? has anyone done studies on that?
do significant gains from reflective surfaces require a certain angle between the light, the surface, and the plant? who knows?

saycheese said:

1)"Mirrors reflect coherent images, but this is completely seperate from if they reflect more or less light"
IMAGES ARE LIGHT!!!!!! This makes no sense.
2)Hot spots not only means temperature but a specific point of greater light intensity.
3)Wavelength impossible to measure?
I think not. Just an expensive device. They run about $250-$300. I can't afford one, can you?

Unfortunately you replied with complete opinion which is exactly what I didn't ask for. None of your information had any scientific or statistical data to back up plus you separated images from being light which is just pure ignorance. Hate to sound so hypercritical but I am finding info on these forums to be of utterly useless as no one is willing to spend the money to buy the equipment to find out real answers. I don't have the budget for a wavelength meter but I'm hoping one of you would seeing as how this would be in the best interest of a professional grower.

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How exactly would this be in the best interest of a professional grower? They CAN and have tested the other reflective materials and they reflect 90+ percent of light. Some as high as 97+ percent of light.

So why put up big ass heavy mirrors in your professional growroom? Why spends $100's if not $1000's on mirrors presumable of custom size? Why deal with taking them down to clean behind them and get everything super clean between grows?

The sheer act of hanging the mirrors is far more difficult than just putting up some mylar or panda plastic. Even if you could prove they do reflect a lot of light, it won't ever be enough to be worth it. That's why you don't see this point argued often. Who the hell wants to deal with all of that?

yeah mirror work just fine
the only plus to useing that other shit
is that mirror's cost way more. the end
to me money is everything but if i could aford it i would use mirror
now i use paint flat white
but at first i tried collecting mirrors
i gat up to 8 of them , the kind you get from target on sale for 10$
the one's you hang on a door

saycheese said:

1)"Mirrors reflect coherent images, but this is completely seperate from if they reflect more or less light"
IMAGES ARE LIGHT!!!!!! This makes no sense.
2)Hot spots not only means temperature but a specific point of greater light intensity.
3)Wavelength impossible to measure?
I think not. Just an expensive device. They run about $250-$300. I can't afford one, can you?

Unfortunately you replied with complete opinion which is exactly what I didn't ask for. None of your information had any scientific or statistical data to back up plus you separated images from being light which is just pure ignorance. Hate to sound so hypercritical but I am finding info on these forums to be of utterly useless as no one is willing to spend the money to buy the equipment to find out real answers. I don't have the budget for a wavelength meter but I'm hoping one of you would seeing as how this would be in the best interest of a professional grower.

Click to expand...

To understand how such mirrors work, let us first describe the interaction of light with some media in the semiclassical view. Light consists of electromagnetic waves, which induce some oscillation of electrons in any substance hit by the light. In an insulator such as glass, the electrons are firmly bound and can only oscillate around their normal position. This movement influences the propagation of light so that its wave velocity is reduced, while there is only a small loss of energy. This is different in a metal, where some of the electrons are free to move over large distances, but their motion is damped so that energy is dissipated. The wave amplitude decays very quickly in the metal--usually within a small fraction of the wavelength. Associated with that decay is a loss of energy in the wave and some heating of the metal. Most of the incident optical power, however, is reflected at the air/metal interface. In other words, the power is transferred to another wave with a different propagation direction (opposite to the original direction for normal incidence on the surface).

In the case of a silver mirror, this reflection occurs at the interface of glass to silver, essentially because the optical properties of the metal are very different from those of glass. (As a general rule, waves experience significant reflection at interfaces between media with substantially different propagation properties.) In the case of this silver mirror, there is also another, weaker reflection at the air/glass interface. In the end we obtain a reflected wave with essentially the same properties as the incident wave apart from some loss of power, which typically amounts to a few percent for silver mirrors.

This reflection loss does not matter for a mirror used in the bathroom, but such metallic mirrors are usually not suitable for use in lasers. The loss of light itself is often unacceptable, and the associated heating of the mirror can cause difficulties, in particular via thermally induced deformations. These affect the spatial properties of the reflected light. For example, bulging of the mirror surface can defocus a laser beam.

Not mine copy and pasted from somewhere luckydog82

The color of an object is the first factor of whether something will
reflect. Some molecules can absorb visible light and hold it long enough to
convert it to heat. This is what makes something look black. Some
molecules release visible light almost as soon as it is absorbed. These
materials look white. Most materials absorb some colors better than others.
These have various colors.

The next concern is smoothness. A rough surface reflects in all directions.
A piece of concrete is a good example. A very smooth surface reflects in a
very ordered fashion, sending most light out in a single direction. This is
a mirror. A good mirror is silvered because of color and smoothness.
Metals are very flexible, very easy to smooth with just a small amount of
heat. Metallic paint produces a very smooth surface. Of all metals, silver
is probably the most "white". It reflects almost every color. Gold and
copper would not reflect blue very well.

luckydog82 said:

To understand how such mirrors work, let us first describe the interaction of light with some media in the semiclassical view. Light consists of electromagnetic waves, which induce some oscillation of electrons in any substance hit by the light. In an insulator such as glass, the electrons are firmly bound and can only oscillate around their normal position. This movement influences the propagation of light so that its wave velocity is reduced, while there is only a small loss of energy. This is different in a metal, where some of the electrons are free to move over large distances, but their motion is damped so that energy is dissipated. The wave amplitude decays very quickly in the metal--usually within a small fraction of the wavelength. Associated with that decay is a loss of energy in the wave and some heating of the metal. Most of the incident optical power, however, is reflected at the air/metal interface. In other words, the power is transferred to another wave with a different propagation direction (opposite to the original direction for normal incidence on the surface).

In the case of a silver mirror, this reflection occurs at the interface of glass to silver, essentially because the optical properties of the metal are very different from those of glass. (As a general rule, waves experience significant reflection at interfaces between media with substantially different propagation properties.) In the case of this silver mirror, there is also another, weaker reflection at the air/glass interface. In the end we obtain a reflected wave with essentially the same properties as the incident wave apart from some loss of power, which typically amounts to a few percent for silver mirrors.

This reflection loss does not matter for a mirror used in the bathroom, but such metallic mirrors are usually not suitable for use in lasers. The loss of light itself is often unacceptable, and the associated heating of the mirror can cause difficulties, in particular via thermally induced deformations. These affect the spatial properties of the reflected light. For example, bulging of the mirror surface can defocus a laser beam.

Not mine copy and pasted from somewhere luckydog82

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I would like to say that I DO believe mirrors are HIGHLY reflective and do not absorb as much light as is told on this website and the other pot growing forums, over and over and over.

It's got to be bullshit. Too much evidence thus far to support that it's bullshit and not enough against.

Mirrors are used constantly in lasers and MANY other devices often to increase the intensity of light. Obviously mirrors can be made with many coatings and you would almost certainly want a silver coated mirror for your grow room to get the best reflectivity, but it's just unrealistic and won't evenly disperse the light. Do I think you could do some dope shit with growing pot with mirrors? Absolutely. Is it practival? Not so much.

You could probably build a room out of zillions of tiny mirrors and be certain to use a lot more of your available light, but it's crazy.

I have been thinking about this exact question for a while now. I agree with most of what you stated and also agree that mirrors are not being given a fair chance. I don't have any hard facts to back up my claims but I have some real world examples that may explain some of the reasons why mirrors are not "ideal".

Mirrors do not CREATE hot spots. if a flat mirror is close to flawless it creates near perfect reflections and therefore not be able to focus light creating any significant hot spots. However mirrors don't disperse any beams of light that hit it. A flashlight will shoot a "hot spot" beam of light that will not be scattered by mirror. This is why I think a more matte surface is preferred. a matte surface will evenly disperse any high intensity light beam that hits it in a focused spot. If matte pattern is even and consistent across the reflector it won't be able to focus light and create hot spots either.

I have an expensive surefire flashlight that demonstrates this perfectly when compared to a regular maglight. Both my surefire and my maglight use highly reflective surfaces to reflect light; essentially curved mirrors. however my surefire has a matte/wavy texture on its reflector while the maglight is mirror smooth. Both lights use incandesant bulbs that heat a filament which gives of light and travels through the glass bulb. the glass bulb (due to its irregular semi spherical shape) shapes the light that passes through it creating focused beams of light. when you look at the pattern of the beam on a wall the difference is easily noticed. The maglight has noticeable light and dark rings and spots on the wall (hot spots/cold spots). The Surefire with the matte reflector shoots a flawless circular beam that evenly lights the surface all the way across the diameter of the beam.

I think the idea around a reflective surfaces is to use the most reflective surface possible that can even out any irregular beams of light that hit it. Mirrors seem to be very good at reflecting light but they do not even out the light that hits it. in a grow room it is inevitable that light hitting the wall will be uneven, therefore the surface of the walls ideally need to disperse any beams that hit it to provide more even lighting. Cost is a big factor. To create walls that are mirror reflective with a wavy finish would be very expensive. My surefire was 10X as expensive as a similar maglight, mainly due to the lamp assembly/reflectors ablilitly to give a smooth beam of light with no hotspots.

sorry for the lack of "facts" but I don't have the time or money to experiment and research these things.

the only bad thing about mirrors are the cost

the end

Try shining a laser in a mirror, the dot that reflects back will be a lot dimmer than normal.

rt5 said:

Try shining a laser in a mirror, the dot that reflects back will be a lot dimmer than normal.

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Just did it....and no, no it's not. And this is just my crappy bathroom mirror. It's not noticeably dimmer.

Don't get me wrong mirrors are highly reflective or else they wouldn't be mirrors but silver will never be as white as white and flat white releases the light back in all directions unlike a mirror which will reflect the light in 1 direction