# Glass lid and light



## Jaap (7 Oct 2014)

Hello,

I have a TMC Aquabar 600 with a controller and week by week I have reached 100% intensity with very good growth and no algae. Now I have added a glass lid onto the tank and it gets alot of condensation on it. 

How much will the clear 4mm glass lid and the condensation drops block my light? Will it be as if it was 80%?

Thanks!


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## Jaap (7 Oct 2014)

Anyone?


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## NattyAntlers (7 Oct 2014)

I would like to know also having just added a 4mm perspex cover and was thinking of asking the same question so thanks.


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## Frenchi (7 Oct 2014)

Well I'm no expert but since I added one, my plants seem to be doing much better .. Less algae for sure .. This tells me that my light was too bright in the first place and the lid has dampened the Rays slightly... But by how much I couldn't tell you  


Sent from my iPhone using Tapatalk


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## drodgers (7 Oct 2014)

IMO I feel there is a 30% reduction from covers and condensation .I do plan on buying a meter so i can read par values.
Be assured that covers are bad for light penetration, just ask any reef keeper .


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## Jaap (8 Oct 2014)

ok so I guess I need to lower the light fixture.....now its 55cm from the substrate....should i go to 50cm and then to 45cm and so forth? I mean a 5cm decrease is good or is it too much?


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## clonitza (8 Oct 2014)

I'll give you a percent in a couple of days for my tank, not sure tonight I have the time tonight.
You can roughly test it with your DSLR and use this calculator to see how much lux you lose when placing the lid on top, based on the difference between exposures: 
http://www.intl-lighttech.com/support/calculators/exposure-value-to-lux-converter

Cheers,
Mike


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## NattyAntlers (8 Oct 2014)

30% reduction seems a lot, I might be coming at this the wrong way but will a layer of condensation under a cover be about the same as topping up the water level by that much.
The light still needs to travel through just water.
Or am I missing something relating to light diffusion?


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## drodgers (8 Oct 2014)

I think its the refraction that scatters the light.Think of the bubbles on the glass like a bunch of reflectors throwing the light sideways etc.
30% may be high but that note you  always will have a hard water film on the glass because of the intensity lighting we use


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## Bhu (8 Oct 2014)

Yes but with r


drodgers said:


> IMO I feel there is a 30% reduction from covers and condensation. I do plan on buying a meter so i can read par values.
> Be assured that covers are bad for light penetration, just ask any reef keeper .



With reefs you get deposits of salts on the glass so definitely a no no. I soon learnt that one and always had an open top on my 6' reef. Also corals especially hard corals like sps are very light demanding. As I'm learning on this forum it appears that plants are not so light demanding as many have been led to believe. So I'm keeping my glass condensation lids for my aquagrow 600's to rest on. Plant growth is great so I'm happy. Saying that I do love these open top aquariums with the water right to the top with no braces etc. Looks fantastic but how do they keep their fish and shrimp in them


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## Jaap (4 Nov 2014)

Can anyone with a PAR meter inform us of the loss in light when using a glass lid?


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## Mr. Teapot (4 Nov 2014)

I was  wondering about this a while back and found some information on reef forums. If memory serves, they weren't overly concerned with loss as it was so little - under 1% (If kept clean!)… a quick dip into the salty forums will be your best bet for more detailed info.

they may of been talking about glass covers on lights not the tanks… it was a while back. Just disregard


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## drodgers (4 Nov 2014)

Jaap said:


> Can anyone with a PAR meter inform us of the loss in light when using a glass lid?



Would love to see the results of a accurate experiment.
Compare high iron glass (green) over clear low iron etc .
I have some lids I have that came with a second hand tank that have mineral etching so bad i bet they block half the light


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## GreenNeedle (5 Nov 2014)

Theres a reef thread somewhere that show this being measured.  30% sounds about right to me with clean glass.  the condensation doesn't play too much of a part really its more dust and salt deposits and the fact that clear glass / acrylic isn't as clear as air.

The reef thread that measured it recorded over 50% losses but that was without cleaning the glass.


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## GreenNeedle (5 Nov 2014)

Here it is.  Just under 50% loss at the top and about 30% loss at the substrate

http://www.livingreefs.com/threads/photosynthetically-active-radiation-par.25217/


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## clonitza (5 Nov 2014)

Before people start pumping photons, scared they have too little light, here's a photo with my tank:



 
I'm using 2x18w T8s / 60l, no reflectors, 10cm above the surface and a plexi lid, most of the time covered in dust.


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## brandon429 (8 Nov 2014)

how do you get that all white background for the photo no see through tank back or sides


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## GreenNeedle (9 Nov 2014)

frosted film on the back.  The sides reflect it


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## Samjpikey (9 Nov 2014)

You could always use a piece of self cleaning glass for a glass lid , this should stop the condensation to a certain degree , as it will have a special coating in which water doesn't like to 'adhere' to , a bit like if you were to spray a surface with silicone spray . 

Just a thought


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## drodgers (9 Nov 2014)

Reference;popularﬁshkeeping.co.uk January-February 2014

Air versus light Living plants depend on the energy from specific wavelengths of light, in order to be able to photosynthesis and thus grow. Simply placing a light over an aquarium will not guarantee that your plants will thrive – it needs to be of the right type. Water itself has what is known as a V value or refractive index. Every transparent item has its own refractive index and it is this index that dictates just how light passes through the medium concerned. Air is denoted by an index
of just 1.00. This means that light travels through air very well indeed, and is not changed very much in terms of concentration or color aberration, meaning that its brightness and color are not affected. In contrast, the refractive index of water is around 1.33 and as such, the light itself entering here will be concentrated into a smaller area and it becomes more subject to both color aberration and color change. In this type of situation, many PAR readings that are taken are inaccurate. A reading from a PAR meter taken through air will always be higher than if the same lamp is directed through water. When checking on the stated PAR level for your aquarium therefore, you should be clear that the figure advertised has indeed been taken through water and not through the air. It is also worth pointing out that if salt is added to an aquarium, even to create a brackish rather than a marine set-up, the refractive index 
increases marginally, and this will still be sufficient to impact on the light and its passage through the water. In terms of cold water or tropical aquariums where live plants are not included, or if low light species of plants are chosen, then the PAR output of a lighting product does not matter too much. Fish are not reliant upon solar energy in the same way as reptiles and birds, and therefore a lower power light fitting can be safely used, without any risk of harm to their health. This light source, however, should be of a sufficient quality to show the fish themselves off in the very best light, so to speak


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## candymancan (9 Nov 2014)

Par is just so confusing.. and kinda stupid if you ask me...  I say put a bright light over the tank that's got at least 1 6700k light and the rest pink and your plants will grow so fast you don't know what to do with them...  and yes I have red plants in my tanks that require high lighting...  Which I was able to grow and keep red/pink using regular T5's normal outputs and a couple plant grow T8'S..

As for glass and acrylic tops taking away light...  You don't need a par meter to tell you that they do...  Take your glass top move it back and forth from under your light in your fish tank (assuming you have a light that rests above the water like mine) and youll see the slight shading over the plants or wood or what not the glass does..  I have tried this with my 10g bowfront and its LEDS that came with the tank..  I moved the acrylic top back and forth and Its pretty noticeable that the top does reflect lighting..  You can even see the ceiling light up a little, same goes for my 44g Pentagon which is using Power Compacts..  I can see the slight shading over my plants and driftwood by removing my glass top and putting it back over..  I would say its about a 10-15% reduction in lighting but it isn't enough to justify keeping your lid off your tank and risk your fish jumping out..

As someone who is an amature astronomer and deals with telescope mirrors which refract and reflect lighting which is a lot more complicated then any of you/us fish tank people will get involved with...  I will tell you this... dust and water stain films on the glass... or what not wont have much effect AT all when it comes to growing your plants..  We in astronomy come across dusty reflecting mirrors all the time or mirror covered in dried up morning dew and so forth and it doesn't affect the amount of light your mirror can see and reflect into your eyes from space which is why you you never clean them...  Cleaning the mirror's is actually worse because of the micro scratches that get put into the mirror's that actually affects the light capturing more then dust will.


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## clonitza (10 Nov 2014)

brandon429 said:


> how do you get that all white background for the photo no see through tank back or sides


The tank is 40cm away from the wall, no background was applied to the back glass.

Regarding the lid, I couldn't live without it, all my fish are jumpy, I've lost a lot of them before adding it and I won't go back, I can always increase the light intensity with reflectors or by adding another bulb.
The evaporation is also high without it cause there's a difference of 5 degrees between the aquarium and the room temperature.



> Simply placing a light over an aquarium will not guarantee that your plants will thrive – *it needs to be of the right type* ...


For sure those 1000 led lamps nobody can live without ... 

Cheers,
Mike


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## dw1305 (10 Nov 2014)

Hi all, 





candymancan said:


> Par is just so confusing.. and kinda stupid if you ask me... ...  and yes I have red plants in my tanks that require high lighting...  Which I was able to grow and keep red/pink using regular T5's normal outputs and a couple plant grow T8'S...... I would say its about a 10-15% reduction in lighting but it isn't enough to justify keeping your lid off your tank and risk your fish jumping out.


 I definitely agree about the lid, I can find quite enough ways of killing the fish without adding another one, and I will always use a cover.

I don't think that any-one is arguing that all light sources are equal in terms of their out-put of photosynthetically active (usable) radiation (PAR/PUR), but it isn't as simple as saying that chlorophyll absorbs light in the red and blue spectra and  reflects it in the green wavelengths.

The argument would be that most colour temperatures of white light (from even fairly modest wattage fixtures) produce enough PAR to exceed the <"light compensation point"> (LCP) of most plants. This is largely to do with the <"accessory pigments"> in the chlorophyll molecule, which will harvest different wavelengths of light from <"chlorophyll a">. 

There is a more complete description in Clive's post here: <"Do T8 lights really degrade..."> or in Kirk's <"Light and photosynthesis in aquatic ecosystems">.

Once we are above LCP the major limiting nutrient for most aquatic plants is inorganic carbon (CO2), so rather than adding more light you need to add more CO2, and as you add CO2 the plants LCP will actually decrease. Light drives photosynthesis, and if we have non-limiting nutrients (including carbon) we can acheive very high growth rates. This was the reasoning behind the development of <"Estimative Index (EI)">. This then leads to the statement that there aren't any high light plants, there are just plants that have a higher CO2 demand.

Problems arise when we have a bright light source in a situation with low nutrient (including carbon) levels, this is partially to do with the <"damage caused by the excess energy from the incident radiation">.  I'll leave the rest of this argument to some-one else, as I'm not a CO2 or EI user, although many use it successfully.

Personally a lot of PAR just means I have a larger plant mass, which I keep in slow active growth via the <"Duckweed Index">. It is a KISS solution and doesn't have the "_bells and whistles_" of EI, but I'm not an aquascaper, so it suits me.

cheers Darrel


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