# The design of a reflector:



## Greystoke (Jul 24, 2010)

Consider the set-up in the drawing:


We have a trapezium design reflector, with a tube inside it. The position of the tube is fixed in relation to the reflector’s surfaces. 
The tube’s downward light beam - directed to the water surface - is intended *to illuminate the full width of the tank from back to front*, by adjusting the reflector’s height above the water. It can also be achieved by modifying the length of the reflector’s *“wings”*
The tube’s upwards beam is captured by the reflector, for the purpose of redirecting it back down to the water. 
There are three areas of concern, where rays are reflected multiple times between reflector and tube. This causes a severe loss of intensity. Multiple reflections *(re-strikes)* cannot be completely avoided, but they can be minimized.
The angle of these re-strike sectors can be exactly calculated. They are a function of T *(tube diameter)* over d *(distance between tube and reflective surface)* In this case each sector covers about 33°of light. The full angle covering all three sectors is about 123° [!] That is a lot of light to lose if it cannot be properly re-directed downwards.
Obviously, the reflector design needs to be optimized in order to minimize this effect.


Method:​ 
If we extend the horizontal reflector above the tube to capture all three sectors, then the two outer sectors will be reflected sideways and not back to the tube. That would be a big improvement, but . . .
How long must that horizontal section be? ​We’ll skip the calculations as they are quite complicated. The next drawing shows the results:






Measurements are given in multiples of the tube diameter T. To find the actual values in inch, you need to multiple these with the tube diameter (ie: T12 = 1.5”, T8 = 1”, T5 = 5/8”)
*(Note that this design has no extended wings yet. An aspect that will be dealt with a bit later)*

So far, this took care of the side sectors, but there is still the central sector bouncing around between the top horizontal reflector section and the tube.
However, there is a simple way to get rid of it.







A small “nick” in the middle of the horizontal reflector will redirect the beams sideways.







Or perhaps like this:










 Where and how to mount the reflector? ​
Of course you can mount the reflector anywhere you wish, back, front, up or down and even at an angle. It will of course all work. However, you will have to relate your method with the general assumption that the reflector is mounted halfway between back and front wall, and mounted straight (not angled).

This is the reference model:









 Skirts: ​This time the reflector has extended wings called a “skirt”, which is intended to reduce the down beam size so that it will cover the full width of the tank. It has a slightly different slope compared to the wings, which save on material and size although achieving the same intended depth.

Note:
In this case the light output covers more than the water surface - and as was mentioned before - this can be adjusted by moving the reflector down (or “up” in case of an under-cover).

Do not waste this carefully selected light outside your tank. That’s not what it was meant for.
If the beam covers the full width of the tank (and it pays to check that now an again), you can be assured that the FULL power of the light source (less the losses in the reflector) is applied to your tank.
Bad reflectors can give you a loss of 40%. Good reflectors are closer to 5 – 10%.


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## Tenor1 (Jan 15, 2012)

Thank you Cor for such an interesting article. It made me look at the old Custom Sealife reflector over my tank. The outward casing is a half-oval shape and luckily the reflective shield on the inside is angled just as your diagram recommends as optimum. I always assumed it was an oval on the inside. After all these years I really inspected it.

Many years ago I read that having a white surface may actually deflect more light that the shinny silver surfaces. Is there any validity to that? My thought was always no, otherwise, manufactures would have converted over to it years ago, but it still crosses my mind.

Thanks again,


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## Tenor1 (Jan 15, 2012)

Does the efficiency of the reflector affect the PAR level? Ecoxotic has reflectors for their light strips and claim in doubles the intensity of the light. But does it really do that?


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## lochaber (Jan 23, 2012)

Tenor1 said:


> Many years ago I read that having a white surface may actually deflect more light that the shinny silver surfaces. Is there any validity to that? My thought was always no, otherwise, manufactures would have converted over to it years ago, but it still crosses my mind.


I think if you have something like polished aluminum, or mylar, they will reflect a good deal of the light, but they are directional, so reflector shape matters. Not mirrors though, they have a pretty big loss.

White paint sorta scatters the light, so it's useful if you don't have an actual reflector, and I don't think the shape is as important. Plus, it's super easy to just spray paint the inside of a hood, and you'll still get pretty good returns for the cost/effort.


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## Greystoke (Jul 24, 2010)

+1,
White paint works very well, but the scattering makes it a bit difficult to fit the down-beam to the water surface. Some of the light will therefore scatter over the edges and get lost.



Tenor1 said:


> Does the efficiency of the reflector affect the PAR level? Ecoxotic has reflectors for their light strips and claim in doubles the intensity of the light. But does it really do that?


Inefficiencies in the reflector are losses, because some of the light disappears, gets absorbed, etc. . .
The other way to lose PAR is by overextending the area covered by the down-beam, wasting light on areas that don't matter.

Not sure about reflectors for light strips. I'm a bit sceptical.


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## adrianjuaneli (Jan 8, 2014)

The details which are shared about the design of a reflector are really very informative. Generally, When the optical design performs to specifications, non-optical pieces that are necessary to complete the design are added. A high-quality calculation of the output verifies that the complete design meets the requirements. If the design passes, the engineer exports the design for prototype fabrication.


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## Hoppy (Dec 24, 2005)

Light travels in either direction, from or towards the bulb, the same way. In other words, you can substitute a source of light for the water and a receptor of light for the bulb, and the optical diagram will be the same. This means you can look up at the light from the perspective of the tank and see how well the reflector performs. When you do this, and it is a lot easier if you remove the light from the tank and hold it sideways, you will see more than one bulb if the reflector is working right. Each bulb you see (each reflection of the bulb) is the same as another bulb, minus a small loss from imperfect reflection. So, it follows that if you see 2 reflections of the bulb, plus the bulb itself, you can get up to 3 times the amount of light from the bulb compared to not having a reflector. And, if you can see 4 reflections of the bulb, assuming they are reflections of the whole bulb surface, you can get up to 5 times the amount of light.

Obviously the more reflected images of the bulb you can see, the smaller each image is, and, therefore, the less light you get from each reflected image. In real life, the two image reflector does give you more than twice the light that a reflectorless bulb gives you. But, with 4 images of the bulb, each image is too small, reflecting only a portion of the light from the bulb, so that you don't get nearly as much from the additional images. AH Supply claims their 4 image reflector gives you about 2.8 times the light that you get from just a flat reflective surface behind the bulb. I have measured the increase in light with a 2 image reflector having reflective aluminum surface only slightly polished. That increased the light by about 2 over what it was with only a flat reflective surface behind the bulb. If the reflector surface had been highly polished aluminum the increase would have been higher.

Where we luck out is that this is a simple way to judge the quality of a reflector: just look at the bulb, and if you see 2 or more complete images of the bulb, plus the bulb itself, and they are bright images easily mistaken for additional bulbs, you have a very good reflector.


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## Greystoke (Jul 24, 2010)

I'm sure your theory is essentialy correct.
However, what confuses me is that you claim to get 2,3,4 and 5 "times the amount of light from the bulb compared to not having a reflector" if you see multiple reflections of the bulb. 

I can understand "2x", ie: You originally lost 50% of the light without reflector, but with reflector you re-captured 100%. So how how do you explain 3,4 and 5 times? You would need to start-off with a loss of 67%, 75% and 80%. You don't normally get such high losses, even without reflectors.


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## Seattle_Aquarist (Jun 15, 2008)

Hi Cor,

You are absolutely correct that having the correct angles in a reflector, and proper reflector material (such as MIRO 4 aluminum) can make a huge difference in the output without needing to use additional lamps that burn expensive watts.

AH Supply has different designs for two different types of lamps, Power Compact and T5HO.



> For any aquarium lighting system, the reflector is of paramount importance. Light striking the water at more than 55 degrees from vertical is simply reflected off the surface. That means that light from only 110° of the 360° tube will enter the water directly. The light from the other 250 degrees (almost 70% of the total) only gets in the water if it is reflected downward at a steep angle.
> 
> To turn both the up-light and side-light downward effectively, A H Supply’s T5 linear system uses a multi-faceted reflector that is slightly larger than most (43.75"L x 2.5"W x 1.125"H) and made of a state-of-the-art, highly polished, coated aluminum. An excellent reflector always beats additional wattage, giving you a system that uses less energy, produces less heat, and has fewer components that burn out.


It's hard to see in the picture but these reflectors for the T5HO lamps have exactly the "notch" you describe.


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## Greystoke (Jul 24, 2010)

Good info, thanks a lot.

I can see the notch and the shape of the reflectors by the form of the cut-off edges.

Those reflectors may have an efficiency as high as 95%.

One other aspect that should be mentioned is to avoid placing more than one bulb under one reflector. Each bulb should have its own reflector.


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## Greystoke (Jul 24, 2010)

Greystoke said:


> I'm sure your theory is essentialy correct.
> However, what confuses me is that you claim to get 2,3,4 and 5 "times the amount of light from the bulb compared to not having a reflector" if you see multiple reflections of the bulb. . .


I think I finally understand the problem . . . 
You (Hoppy) speak of *intensity at a point*, whereas I speak of *total quantity* of light.

If you regard a reflector as a light concentrator, then - obviously - the light intensity directly underneath the reflector depends on its ability to do so, and - depending on that ability, you could - in theory - get any number of multiplication.

But is this really what we want?
If you look at my post, then the obvious aim of the reflector is to redirect "stray" light downwards and then even it all out across the top surface of the tank as much as possible.

That's about maximising the total output of a light source for the benefit of the aquarium.

That - in my opinion - is a big difference of approach.


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## Hoppy (Dec 24, 2005)

If a reflector reflects 100% of the light striking it, then it is obvious (to me, at least) that if you see a reflection of the whole bulb when you look at the reflector, and the reflection is the same size as the bulb, you must be getting the same amount of light from that image of the bulb as you get from the bulb directly. Therefore, if it was possible to get 4 full reflections of the bulb, you could get 5X the amount of light that the bulb alone gives you. Of course, to do that, the reflector would have to be large, and quite a distance from the bulb, or each reflection wouldn't be full size (5/8" wide for T5 bulbs). In fact, with more that one image of the bulb on each side of the bulb, each image is only of a portion of the bulb. I think that is why AH Supply reflectors give "only" 2.8 times the light as a poorly reflected bulb, which is probably more than 3X the light of a bare bulb.

Yes, I am referring to the light as measured with a PAR meter, at one spot, directly under the center of the bulb, just as your eye "measures" the light at only one spot when you look at the bulb/reflector. I don't know of any way to measure the total light from the bulb, integrating the light over the whole tank, so I stick with the single point measurement.


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## Zorfox (Jun 24, 2012)

Very informative thread thanks for the post! I'm in the process of deciding how I want to light a 240g. It has a canopy that is falling apart. The ballasts are very nice with individual reflectors. However, they are either T12 or T8 VHO bulbs, never measured them (yes I'm a lighting noob lol). I expected to convert to T5HO bulbs since the ballast will work for them using the same reflectors. Now I'll have to rethink this. Is it possible to buy just reflectors at a reasonable price? Otherwise, It may be cheaper to buy a finished system.


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## Greystoke (Jul 24, 2010)

Hoppy said:


> Yes, I am referring to the light as measured with a PAR meter, at one spot, directly under the center of the bulb, just as your eye "measures" the light at only one spot when you look at the bulb/reflector. I don't know of any way to measure the total light from the bulb, integrating the light over the whole tank, so I stick with the single point measurement.


Fair enough, but . . .
there's no need to measure the entire output. It can be accurately estimated - within a few % - if you know the luminous output of the bulb. Then - if the K-rating is known - there is a fixed relation between Lux and PAR.
My only concern with your method is that spot-measurements and accurate averages across the whole tank are questionably related, and that's a value that you should really know.


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## Greystoke (Jul 24, 2010)

Zorfox said:


> Very informative thread thanks for the post! I'm in the process of deciding how I want to light a 240g. It has a canopy that is falling apart. The ballasts are very nice with individual reflectors. However, they are either T12 or T8 VHO bulbs, never measured them (yes I'm a lighting noob lol). I expected to convert to T5HO bulbs since the ballast will work for them using the same reflectors. Now I'll have to rethink this. Is it possible to buy just reflectors at a reasonable price? Otherwise, It may be cheaper to buy a finished system.


By all means keep individual reflectors. That's well worth the price.


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## Hoppy (Dec 24, 2005)

My whole focus, with PAR measurements, has been to find a number to use to rate lighting, that replaces "watts per gallon", but is much, much more accurate. So, I settled on the PAR at the substrate, in the center of the tank, knowing that the PAR at other locations in the tank will be different. For a given type of light fixture the variation in PAR around the tank should be about the same for every aquarium - it goes up as you measure nearer the water surface, and it almost always drops off near the ends and front/back of the tank. So, if I say, as I do, that 25 PAR, at the substrate in the center, is low light, but enough to grow many kinds of plants, I don't mean that each plant sees 25 PAR, just that the PAR that they do see, when it is 25 at the substrate in the middle, is low light and adequate for many plants. All of the plants that grow to the water surface obviously see a lot more than 25 PAR, and plants at the back or ends of the tank probably have to make do with less than 25 PAR.

Maybe some day I will be interested in looking more at the actual PAR where a plant is located, and the actual PAR at the bottom of the plant, the middle and the top.


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## Greystoke (Jul 24, 2010)

This was a good discussion. Your explanations make a lot of sense to me now.

One last concern . . .

Light propagation down the water column depends on: turbidity, reflections, fish and vegan obstructions, just to name a few. Those are not constant effects and therefore your spot-measurement is not a "given" constant.

I refer here to a post by someone who had grown a floating cover and he wished to know how much difference that would make to his light.
I replied that since he/she is the only one who can make an intelligent guess of that effect, it is his/hers responsibility to pick a number.

What advice would you have given?


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## thinBear (Dec 16, 2011)

Very informative discussion. I think a CAD program like Maya should help design and simulate how well the reflector work?


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## Greystoke (Jul 24, 2010)

thinBear said:


> Very informative discussion. I think a CAD program like Maya should help design and simulate how well the reflector work?


I have an Ecell program designed by myself, but its a bit limited. I'd be interested to hear how this Maya program would work.


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## thinBear (Dec 16, 2011)

Greystoke said:


> I have an Ecell program designed by myself, but its a bit limited. I'd be interested to hear how this Maya program would work.


Sorry hope I could help, that's a question I put there...I'm not good in both lighting and CAD

I've heard Maya/sketchup with VRay plugin before, but it seems not exactly the software we talk about here...


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## Greystoke (Jul 24, 2010)

Never mind thinBear,
I will upload my Excel-program, just to see what people think about it.

Here it is:
Reflector Efficiencies


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## Zapins (Jan 7, 2006)

Very nice explanation and detail in this thread Greystoke, you have obviously given this a lot of thought!

I've always liked AhSupply lights, but they are made for dual tube power compact bulbs which have a lot more restrike than normal T5 HO.


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## Greystoke (Jul 24, 2010)

Thanks for the compliment Zapins.

Yes, I think CFL's are useful, particularly for nano tanks, but they are a bit overrated. A lot of people do not realise that they pay for a 25% power loss (or more) due to this inherent re-strike problem.


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