Done with mirrors

DesertPlants said:

I personally never use mirrors because it not only creates a focused reflection, it creates a focused heat spot. I have found much better results using Orca Grow film. It's a flat white and diffuses the light giving even reflection and doesn't create hot spots. It also helps increase the number of angles light hits different parts of the plant. If you think about it in terms of geometry, instead of reflecting at an equal and opposite angle, it spreads the reflection out and can add light to areas that would otherwise not get it.

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A reflection cannot be as intense as the original without being focused. Mirror reflection is approximately planar. Not arguing against diffusion (provided by orca, flat white and others), I belive it is benificial too.

SSGrower said:

A reflection cannot be as intense as the original without being focused. Mirror reflection is approximately planar. Not arguing against diffusion (provided by orca, flat white and others), I belive it is benificial too.

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Yeah, I wasn't saying it would be as intense, only it ADDs to the limited area of heat focus. There are benefits to both approaches. Like everything in growing, it really depends on your specific setup and conditions.

The measurements I took using mirrors didn't indicate the presence of hot spots. The increase in light was fairly even across the board. It could be a different story if using high wattage bulbs but with most LED setups this should not be a concern.

Higher par readings seems like a good sign. I'm still in the process of figuring out what it translates into, but so far so good.

Rahz said:

The measurements I took using mirrors didn't indicate the presence of hot spots. The increase in light was fairly even across the board. It could be a different story if using high wattage bulbs but with most LED setups this should not be a concern.

Higher par readings seems like a good sign. I'm still in the process of figuring out what it translates into, but so far so good.

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All other issues aside, (weight, airflow, configuration...) would you expect any increase if the light were covered with mirrors? What about the floor? Now rotate the room, vertical garden.

DesertPlants said:

Yeah, I wasn't saying it would be as intense, only it ADDs to the limited area of heat focus.

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This makes no sense. How would mirrors even cause hot spots? It's a flat surface.

If you look in a mirror do you see some parts of your face suddenly lit up brighter than others?

SSGrower said:

All other issues aside, (weight, airflow, configuration...) would you expect any increase if the light were covered with mirrors? What about the floor? Now rotate the room, vertical garden.

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I like the idea having mirrors in the upper half of the walls and flat white further down. Mirrors should help to keep the highest intensities in that area where the colas are growing.
Flat white on the floor makes sense as long as the plants are small and the canopy still open. But would be a pita to keep it clean..

Randomblame said:

I like the idea having mirrors in the upper half of the walls and flat white further down. Mirrors should help to keep the highest intensities in that area where the colas are growing.
Flat white on the floor makes sense as long as the plants are small and the canopy still open. But would be a pita to keep it clean..

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Ive thought of using dry erase marker board. May cabs are lined with white melemine laminate.

In my case I'm thinking I can raise the lamp a few inches more than I would usually run it and even out the canopy coverage further without loosing a notable amount of intensity. Measurements indicate the mirrors are doing a good job keeping the light in play at distance so it could end up being a better diffusion method with the right hanging height.

wietefras said:

This makes no sense. How would mirrors even cause hot spots? It's a flat surface.

If you look in a mirror do you see some parts of your face suddenly lit up brighter than others?

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Yes... how do you think salt solar heaters work? They tend to use parabolic mirrors... but same concept. It’s focusing photons in a concentrated area. And if you focus photonics energy, it’s converted to thermal energy when it hits the plant. Like I said, I had issues with that and that is why I switched to white diffusion. It depends on your light and size of grow area for how big of an issue it is. In my case I was using a 2x4 grow area with almost 75 watts per square foot.

@welight how would this perform in your simulation?

DesertPlants said:

Yes... how do you think salt solar heaters work? They tend to use parabolic mirrors... but same concept. It’s focusing photons in a concentrated area. And if you focus photonics energy, it’s converted to thermal energy when it hits the plant. Like I said, I had issues with that and that is why I switched to white diffusion. It depends on your light and size of grow area for how big of an issue it is. In my case I was using a 2x4 grow area with almost 75 watts per square foot.

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If your light intensity is hitting at or near 1500 already that's a DLI of 64 at 12/12. It's not a matter of creating a focused hot spot so much as increasing the average PPFD above what is already bordering on being too much light.

In such a case mirrors might allow the lamp to run at a lower wattage or less time for the same effect.

I'll report back after a few cycles because that's the real indicator, but looking at the data... well first, see that 453 # in the mirror result? I'm about 100% positive that should have been +553. I was taking measurements quickly, hunched over in a closet and I screwed up, either that or more likely I mistakenly looked at the plastic numbers when I was transcribing the mirror numbers because that location is also 453 for the plastic.

Panda Plastic 15" from sensor
412 551 693 745 812
453 665 915 964 1038

Mirror 15" from sensor
573 647 800 852 907
453 760 957 1016 1070

Here's the full data set extrapolated with the 453 to 553 correction. Logically it should be corrected to around 600, but we'll go with 553 to err on the low side.

Panda Plastic 15" from sensor
412 551 693 745 812 745 693 551 412
453 665 915 964 1038 964 915 665 453
412 551 693 745 812 745 693 551 412

Mirror 15" from sensor
573 647 800 852 907 852 800 647 573
553 760 957 1016 1070 1016 957 760 553
573 647 800 852 907 852 800 647 573

If you examine the outer areas you see the average increase is around 100 PPFD (slightly more), but in the center row away from the edges the increase drops, with the center (in bold) only showing an increase of 32 PPFD. That's the opposite of creating a hotspot, but all readings are still more intense. The lower this lamp is hung the less the center will be increased, so from a hanging height of 8 inches (normal height for this lamp) to 12 inches, I should experience almost no change in light intensity in the center while still providing a boost to the outer edges. From past experience, readings from 8 inches top out at around 1300 directly under emitters, so I'm in no danger of blasting them with too much light.

I should probably take measurements from 8 and 12 inches to see what's actually going on at that level.

My lights sit about 18-24" away. Again... this was my scenario and my issue. When I changed to white I got a decrease in the center (again, 2x4 grow area, so in my case the center was the middle 2x2 area). Like I said before... just like most things in growing, it depends on your setup and your conditions. In MY case, switching to a flat white diffusion helped decrease the hot spot in the center. Yours obviously is not the same.

Yes I did mention results would vary based on source and hanging height. 24" height in a 2' wide area is perfect for reflecting the side light back to the center. The same could be true of a 1000w bulb hung at 36" in a 5x5.

I think that using many lower powered light sources would prevent it from being an issue at any height. My rig uses 30w emitters at roughly 1.3 emitters per square foot.

Rahz said:

Yes I did mention results would vary based on source and hanging height. 24" height in a 2' wide area is perfect for reflecting the side light back to the center. The same could be true of a 1000w bulb hung at 36" in a 5x5.

I think that using many lower powered light sources would prevent it from being an issue at any height. My rig uses 30w emitters at roughly 1.3 emitters per square foot.

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Agreed. I am trying different grow lights I am building and seeing what I get the best results with. The one I am using right now,. I made from Vero 29 SE C bin COBs, which create too big of a hot spot. Next grow I am going to use the one I built using B COBs. Twice as many cobs with half the wattage per cob. Should do much better with spreading the light and heat out.

SSGrower said:

@welight how would this perform in your simulation?

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I suspect that reflective surfaces like mirrors will manifest every slight artifact of the original light source, making for a less than clean light, it would require super fine calibration in terms on relationship with light and mirror
Cheers
Mark

3M makes a product engineered for lining illuminated signs. Light Enhancement Film 3635-100. Features "94% plus reflectivity" and is a thin film bonded to adhesive backed paper. Seems ideal for lining grow boxes except that it only comes in two sizes: 4' x 30' and 4' x 150'. Some vendor needs to buy some and divvy it up.

DesertPlants said:

Yes... how do you think salt solar heaters work? They tend to use parabolic mirrors... but same concept. It’s focusing photons in a concentrated area.

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These are flat mirrors not parabolic. You need to focus the light with curved surfaces to get hot spots and you don;t do that with a flat wall of flat mirrors.

If you had problems then you did something else wrong.

With mirrors you get an exact reflection of the light coming from the source. ie you get the same spread as you got from the COB or the strip. From the plants point of view it's exactly like you had that source behind the mirror.

wietefras said:

These are flat mirrors not parabolic. You need to focus the light with curved surfaces to get hot spots and you don;t do that with a flat wall of flat mirrors.

If you had problems then you did something else wrong.

With mirrors you get an exact reflection of the light coming from the source. ie you get the same spread as you got from the COB or the strip. From the plants point of view it's exactly like you had that source behind the mirror.

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DP didnt do anything wrong. He was at 75 watt/sq foot already. Take a given location on his canopy. The light incident on it directly from the light source is of quantity x. Reflected light pases throught that same area in quantity y. X + Y was more energy than the plant could use.

welight said:

I suspect that reflective surfaces like mirrors will manifest every slight artifact of the original light source, making for a less than clean light, it would require super fine calibration in terms on relationship with light and mirror
Cheers
Mark

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If the light source is ideal spectrum then I guess I'm not understanding correctly because it sounds like your saying it would contaminate the quality of light?

SSGrower said:

If the light source is ideal spectrum then I guess I'm not understanding correctly because it sounds like your saying it would contaminate the quality of light?

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not the quality, its likely you could end up with shadows or colour separation issues, when you have high values of reflection, you tend to get every little thing reflected. I dont see it as a dealbreaker but just to be aware of in design consideration