For my graduate engineering thesis, I decided to attack a known problem in my biggest hobby rather than in my actual career field (let’s face it, writing about aquariums is a lot more fun for me!) Coincidentally (or maybe it was fate?), the metal halides on my display aquarium died at the same time. So, I set about learning everything I could about LEDs. This series will include portions of my thesis, but I will try to leave out the portions that specifically addressed my degree requirements. Maybe if I’m brave enough, I’ll post the full thesis eventually.
CHAPTER 1 – INTRODUCTION
Problem Introduction, Relevance, and Importance
For decades, aquarists have attempted to maintain captive marine ecosystems through various lighting technologies, such as normal fluorescents, high output fluorescents, power compact fluorescents, metal halides, and even plasma fixtures. Coral grown in these ecosystems are usually photosynthetic and have high light intensity and specific spectral needs. Additionally, the user tends to prefer a lighting system that has a low life cycle cost, does not exude large amounts of heat, and is customizable. Unfortunately, the aforementioned lighting systems do not usually meet all of the needs of the aquarium inhabitants or the user.
Recently, aquarists have started to turn to light-emitting diode (LED) fixtures since they have high potential performance, a low life cycle cost, run relatively cool, and offer many controllable features. To meet the demand, companies all over the world produce aquarium-targeted LED fixtures. However, these fixtures appear as though do-it-yourselfers (DIYers) haphazardly designed them through trial and error. Therefore, most LED systems have a limited spectrum output, have a shorter-than-designed life, have a high mean-time-between-repair (MTBR), and/or have a high mean-time-between-failure (MTBF).
Using the systems engineering process, an LED fixture for a sustainable captive marine ecosystem was designed and built. The “Light-Emitting Diode for Sustainable Captive Marine Ecosystems” project assessed the lighting needs of typical corals and other photosynthetic invertebrates, requirements of aquarists, and determined a suitable design. In addition, basic “rules-of-thumb” were developed and/or refined to help other interested aquarists design their own system. The system was built and integrated with a controller in order to manipulate the lighting schedule, spectrum, and intensity. The requirements analysis was completed in ENM 595, which outlined the user and aquarium inhabitant needs and wants. The systems engineering analysis was completed in ENM 505, which covered the work breakdown structure, schedule, risk analysis, and preliminary designs. In ENM 590, the chosen design was built, integrated with control equipment (internet-enabled devices and an analog interface), and tested, all while adhering to the systems engineering process.
The largest international forum for saltwater aquariums (ReefCentral.com) has over 240,000 members. Many countries (especially Germany, Italy, Thailand, and Japan) have world-renown aquariums, and the United States is quickly reaching the bar. If a fully functional, maintainable, high performance, integrated, and cost-effective LED lighting system was developed, the demand already exists worldwide. The payback period for this light fixture first article build is less than three years with no profit margin.
Problem and Research Statement
Inefficient and high maintenance lighting fixtures have dominated the reefkeeping hobby for decades. LED fixtures are breaking their way into the mainstream due to their efficiency rating and low maintenance costs, but most fixtures are lacking in features, capability, or performance. This project will attempt to apply scientific research and the systems engineering process to a design.
An LED lighting system was built that met user and inhabitant needs while following the systems engineering process. It addressed environmental concerns, such as the minimization of corrosion from salt creep and humidity and the regulation of fixture temperature. Light intensity is sufficient for the most demanding species of coral in the hobby while featuring a dimmable function to simulate deep-water conditions for more sensitive animals. The spectrum available is fully customizable by the user, but it targets the spectral characteristics of sunlight penetration through 30 feet of water. It also simulates the spectrum and phase (intensity) of moonlight throughout the month to entice spawning within the aquarium. Through integration with a controller and specially designed power heads, the light fixture can simulate clouds, tides (matched with the time of a specific geographical location), and storms. A rudimentary sunrise/sunset function is also available. If this lighting system was adapted for a six foot or longer aquarium, then the sunrise/sunset function would be fully operational. However, this system was designed for a four-foot long aquarium, which limited the feature.
A user-survey was developed and distributed across several reefkeeping online forums, including the Wasatch Marine Aquarium Society, Reef Central, and Nano-Reefs. Additional user statistics and requirements were gathered from Facebook and Reef Central.
Scope and Limitations
This project demonstrates initial basic research in a particular field, through requirements analysis, design, first article build, and initial testing. The first article build will be the only article built, as this system will not be available to the public. This project consists of three phases. Phase 1 coincided with ENM 505, the systems engineering analysis, and ENM 595, the system requirements analysis. Phase 2 coincides with ENM 595, where the system was built and underwent initial verification, validation, and an overall test and evaluation conducted in compliance with the systems engineering process. However, the majority of testing will occur in Phase 3, which will take place outside of the graduate engineering program. Corals can take up to six months to show a photosynthetic response to lighting changes, so the majority of this long-term testing will not be included.
A captive marine ecosystem is essentially an aquarium that simulates an ocean environment. For example, there are aggressive fish tanks, coldwater-species tanks, species-only tanks, and the typical reef aquarium, which contains various peaceful species of warm-water inhabitants. Three main types of aquariums dominate the hobby: the fish-only (FO), the fish only with live rock (FOWLR), and the coral reef. (Bridges, 2013)
Contrary to popular belief, corals are invertebrates, not plants. They consist of a growing calcium-based skeleton, tissues, a mouth with digestive tract, and tentacles. Most corals also contain symbiotic photosynthetic algae, called zooxanthallae. This alga provides the coral with the majority of its energy in the form of sugars and proteins in exchange for the coral to provide it a safe habitat in which to live. The coral can expel the zooxanthallae under various conditions (stress, overpopulation, et cetera), and if zooxanthallae populates declines too much, the coral can catch its own food with its tentacles and digestive system. (Bridges, 2013)
There are two main groups of corals: the hard (Scleractinian) and soft (Alcyonacea) corals. Soft corals, as the name implies, do not build solid skeletons; they build calcium particle splinters, called “sclerites”, that they can arrange as a simulated skeleton. These corals are, in general, quite tolerant of poor water and lighting conditions, but they are often less attractive and are more toxic than hard corals. Scleractinian corals are the reef builders since they build calcium-carbonate skeletons that eventually form most rocks on a reef. They are further subdivided into two groups based on the coral polyp relative size (small and large). Small-polyp Scleractinian (SPS) corals are the most demanding of their water conditions and lighting. (Bridges, 2013)
The main components of a coral reef aquarium are the tank itself, stand, lighting system, flow system, nutrient import/export, heating/cooling system, and the substrate. The lighting system required depends on the inhabitants. FO aquariums perform quite well with normal fluorescent (NO) lighting. Power compact (PC) fluorescents are mainly used for FOWLR aquariums, although they can be used on FO and some coral reef aquariums. T-5 very high output (VHO) fluorescent lighting is an excellent choice for reef aquariums, as well as FO and FOWLR tanks. However, they do not have quite the intensity capability as metal halides, and they are subject to a red-shift phenomenon within about a ten-month period. Metal halide (MH) lighting is currently the most powerful, and it is typically used to light the most sensitive and demanding aquariums. Although MH have a great intensity profile and spectrum, they still often require supplemental lighting in the blue region (as the T-5 bulbs mentioned) to help offset the red-shift trend that the bulbs have over a single year before they require replacement. Each of these systems has its own positive and negative characteristics. For example, NO lighting systems are not sufficient for most coral, but metal halide systems can have prohibitively high electrical requirements. Due to these characteristics, many aquarists have started to make the transition to LED systems. LEDs do not shift in color (minor shifts are negligible), and the components specified in Phase 1 retained 70% of their intensity after ten years. Additionally, LEDs come in a variety of colors and create a customized spectrum with various color combinations. Japan and other countries often use LEDs to create spotlighting effects to highlight particular corals or the rockwork structure. LEDs produce less heat and are more efficient than metal halides, and their light output is quickly gaining in capability. (Bridges, 2013)
Currently, most LED lighting systems are only meeting the “budget-minded” segment of the reefkeeping hobby and industry, as the systems are not aesthetically pleasing, performance oriented, or well-designed for the life cycle. Most systems on the market were designed through trial-and-error, without a requirements analysis. As a result, systems are either overpowered, underpowered, lack control, or emit an unhealthy spectrum for the coral. Additionally, the user tends to prefer a lighting system that has a low life cycle cost, does not exude large amounts of heat, and is customizable. Unfortunately, the aforementioned lighting systems do not meet the needs of the aquarium inhabitants or the user. With a target population of nearly 300,000 people worldwide, many of whom spend thousands yearly on their aquariums, there is a market for such a performance LED system. (Bridges, 2013)
As an example, the author’s 200-gallon display system currently uses two 400-watt metal halide lights, two 54-watt T-5 lights, and LED moonlights. A lighting system of nearly 1000 watts produces an excessive amount of heat. To prevent the aquarium from overheating, two fans blow across the water surface for evaporative cooling. This additional electrical cost increases indoor humidity and requires frequent aquarium refilling with specially filtered water. The overheating issue also requires a specialized controller with a temperature sensor. When the water temperature rises above a specification, the controller turns the lights off. The maintenance costs on the lighting system alone are approximately $200 per year, the electrical costs are over $480 per year, and the initial equipment purchase price was nearly $2,000.
The material budget for this lighting fixture project was $1200, which will have no annual maintenance costs, and the expected electrical costs are less than $200 per year. It will also save water, help prevent mildew issues indoors, and will increase the time the aquarium can go without human intervention.
The views and opinions expressed or implied in this paper are those of the author and should not be construed as carrying the official sanction of the University of Dayton, the Engineering Department, or of individuals/groups mentioned in this paper. This project is for informational purposes only, and it should not be used replace proper electrical engineering training before attempting such a project. Any projects arising from this paper are at the reader’s own risk. Additionally, this report and analysis shall not be used for commercial and/or profit without the author’s explicit written permission and any permission required from the University of Dayton.