LEDs, or Light Emitting Diodes are direct current (DC) electronic components that produce light as electricity passes through them. They have been used for years in home electronics but until recently they have not been powerful enough or had the lifespan to price ratio to compete with traditional aquarium lighting. Today that is changing and as LED technology advances it is quickly moving into the aquarium hobby. Several vendors are producing very nice fixtures, but with the technology still in its toddler years and a limited product selection due to patents in the U.S. many people are taking on the challenge of lighting their reefs with LEDs by themselves.
This article is divided into three parts. Part 1 will focus on the basic ideas used in typical DIY reef LED lighting systems. Part 2's focus is on the components that can be used. Part 3 is how to choose components and implement ideas and components to design and build an LED fixture to best fit your reef's needs. After reading all three parts, you should have gained some general knowledge of how LED lighting works in reef keeping, how to pick out the LEDs that will fit your needs, some of the typical options or configurations and how to piece it all together into a working system. Before getting into a build I suggest you have some basic knowledge of how DC circuits work, what voltage, current, and resistance are, and also how they relate to one another (Ohm's law).
Rethinking Reef Lighting
Secondly, if an LED fixture is built properly it will out-perform and out-last most of the current available reef lighting solutions. To consider performance, I think it is best to consider efficiency by PAR ratings & power consumption(watts) compared to Metal Halide or T5. As a general rule, when comparing PAR : wattage ratio of an LED fixture with high-quality emitters to traditional aquarium lighting setups, you can get an approximately equivalent amount of light with only one third traditional wattage. LED will have a higher up-front cost but it should be offset over time by energy savings and bulb replacement cost savings. Most LEDs used in reef settings have a estimated use of about 50,000 hours before we start to see some spectrum shift. Running at 12 hours a day, that equates to about 11 years of use before replacement costs come into consideration. Compare that to the 9-12 month replacement time frame on traditional bulbs and you can see how the cost savings can come back quickly.
The Direction of Light
LED lighting is also different from metal halide and fluorescent lighting because you will have many small point sources of highly directional light. This means we see very little wasted light going off in random directions. Take for example a metal halide bulb in a lumenbrite style reflector, even though the reflector has "99% reflective material" on the inside, a lot of the light energy is wasted as it bounces around in the reflector before finally being directed to the water surface. Also, consider that the light intensity change over distance is not linear(inverse square law), meaning that *if* light traveling 1" from source to destination has a PAR of 1000, then at 2" it should have 250 PAR, 4" it should have 62.5 PAR... and this is before the light even touches water... With this in mind it should start to become more clear how LEDs can produce so much PAR for so little power. This does come with the disadvantage that a light source directed in such a manner is not good for ambient lighting and as such your reef may seem slightly darker even if its inhabitants are actually receiving more intense light.
Check back for Part 2 which will discuss the components of an LED fixture.