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Lighting recommendations for 20” cube?


ChrisIsBored

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20”x20”x20”

 

I think it comes to about 36G

 

not planning a heavy SPS presence, but it would be nice to have the option.

 

Was looking into the Hydra 32HD but a friend told me it would be overkill.

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On 9/8/2020 at 7:14 PM, DSA65PRO said:

20” Reefbar Pro 50/50 from 21ledusa dot com. Add the Sunsetter controller and it’s just over 100. 

That's not really enough light for a 20" cube tank. They put out less than 100 PAR at 21" directly under the 90 degree optics. To get full coverage the light would need to be 14" 10" above the surface meaning you only have 100 PAR at 11" below the surface directly under the light. Even for a softie tank that's really low. If you are getting two to allow you to get a reasonable PAR level and good coverage, you might as well buy a higher quality light. One of these would work for a shallow, long, and narrow tank, but would be a really bad choice for a deep cube.

 

A Hydra 32hd wouldn't be overkill for a tank this size and would be a great choice.

 

Edit: I solved for hypotenuse instead of height! That's what I get for sleeping through geometry 17 years ago.

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On 9/8/2020 at 2:54 PM, ChrisIsBored said:

20”x20”x20”

 

I think it comes to about 36G

(20•20•20)/231 = 34.6 gallons.  👍

 

On 9/8/2020 at 10:15 PM, jservedio said:

To get full coverage the light would need to be 14" above the surface meaning you only have 100 PAR at 7" below the surface directly under the light.

I'm not familiar with these specific lights BUT based on the info given in the thread so far...  

 

Mounting height is proportional to coverage radius at 90º.....so 10" height = 10" radius of coverage.  (Other lens angles require a little more math.)  About 10" high would do it to get "full coverage" for a fixture with 90º optics on a 20"x20" tank...which would get all 40x20" of that light into the tank.

 

This is 90º at 10" as viewed from the narrow side of the light fixture:

(cube tank with strip light, viewed from the narrow end of the light bar.)

550372171_ScreenShot2020-09-15at3_23_06AM.png.e104839f3616c570fca7a06ce56c0b83.png

The bottom, where direct PAR is lowest, benefits a lot from the "extra" light provided by those side reflections – corals can make good use of that reflected light.

 

Same view with light at 14":

328128486_90@1422over2022cube.png.ed40d32f0d3ccf5e4b5bd041168aff7a.png

You can see how much light is just being wasted over the rim of the tank.  Side-lighting suffers for it.

 

Better to have a strip light even lower than 10" IMO.  

 

Mounting right on the tank trim would be ideal from a lighting perspective.  (Again not familiar enough to say if this is a good idea for this light....I'm talking light bars generally.)

 

Lower mounting with 90º lenses skews the PAR higher and deeper and gets all that "waste light" into the tank, so I think it would be fairly adequate, if not very ideal from a coverage standpoint.  90º lenses leave a lot of "top shadow" when mounted this low, but intensity will be much better:

(greenish is water....blue is light.)

1772117988_ScreenShot2020-09-15at2_09_14AM.png.abebd19082b2c341609033bd63a50181.png

The green area in the diagram is basically un-lit.  This is fine if your coral structure is very low to the bottom, or when your frags are small.  

Corals will tend to grow inside the blue area and will "arch" toward the light once they reach that greenish border area.

 

You can see the light reflected off the glass in the darker triangles of blue at the bottom of the tank diagram.

 

On a tank with so much front-to-back surface area and depth, I think it would be worth adding a second bar – one in front, one in back.  (Could even do three fixtures, depending on space, etc.)

120335640_ScreenShot2020-09-15at3_33_40AM.png.8e78c99a80610fc01fe2f938807800f3.png

 

 

I'd also consider a Kessil setup with wider optics. It allows lower placement and gives more side-lighting.   

 

Either the A160 or A360 could work depending on budget and preferences.  But the a360's are 90 watts like the Hydra32's and probably a better fit.  Controller is optional on the Kessil and can be added later if that's worth considering.

 

The same tank with wide-angle kessils (and a 4" mounting height) would be more like this:

761484746_ScreenShot2020-09-15at9_53_33AM.png.d615502ea4f9371c53542b7ce49270a2.png

 

Note the unlit greenish "top shadows" are completely gone now.

 

You can also see how much more reflectivity there is in the tank vs more narrow lenses....this has a significant impact on side-lighting for your corals. 👍  Over 75% of the tank has excellent side-light coverage now.

 

The Hydra is a pretty good fit at 90 watts.  But at 60 watts it seems like even the Prime 16HD would be fine, if slightly marginal.  Budget wasn't mentioned, so either way.  The 90º lens diagrams at the top apply to these AI's too.

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9 minutes ago, mcarroll said:

About 10" high would do it to get "full coverage" for a fixture with 90º optics on a 20"x20" tank

Yeah, I fixed my post - I solved for the hypotenuse instead of the height and din't bother sanity checking. It's been 17 years since high school geometry and the last time I was solving triangles. Either way, it's a terrible fixture for that tank still only gets 100 PAR half-way down directly underneath.

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On 9/8/2020 at 10:15 PM, jservedio said:

That's what I get for sleeping through geometry 17 years ago.

:lol:  Man, I had to retake Geometry.  😴 

 

It was a long time ago, but as I recall, too much time was spent on postulates and theorems that made no sense/had no relevance to me.  I think geometry was made more complicated to learn than it really is, and was made boring in the process...but I could be wrong.

 

If someone had shown me aquariums as as the practical example for the teachings in class, things may have been different cuz I pretty much get it now that I actually use it.  🤷‍♂️

 

Check out: Online Triangle Calculator

 

I wrote that article when I started doing lighting diagrams like above.  The article shows the triangle calcluater I use for any non-90º angle lenses.  The Pythagorean Theorem is one of the only things that actually stuck with me out of high school Geometry....but a dedicated triangle calculator makes it eminently more useful.

 

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