My Thoughts on Reef Aquarium Lighting Generally, I avoid answering questions such as ‘Which light is best?’ or ‘Need advice on lighting.’ Let me explain why and provide some thoughts. Will ‘T5’ lamps adequately light a reef aquarium. Yes (T12s too, for that matter.) Metal halides? Of course! LEDs? You bet. As I stated in my book ‘The Captive Reef’ (published 20 years ago), almost any light source will provide adequate radiation to support photosynthesis in corals, Tridacna clams, and marine algae. But no light is perfect (even sunlight can create a hostile environment in which some animals cannot thrive.) Requests sometimes ask if ‘Brand X’ is suitable. Although I have tested lights for years, I have not tested every light currently on the market. These sorts of requests are best answered by those with experience with that particular brand. To properly address the proper application of any light source, we must consider many things, including: · Will the aquarium house only fish, or fish and corals and other photosynthetic invertebrates? · If maintaining corals and other invertebrates, which ones? Some animals (such as some false corals) thrive in low light, while at least some Tridacna clams can use as much light as is generally possible in an aquarium. · Can you check and monitor light intensity? Best done with a PAR (quantum) meter, although a lux meter is better than not checking at all. · Aquarium size (LxWxD) · What sort of lighting do you plan to use (LED, metal halide, fluorescent (T5, HO, VHO, regular output, mix of any of these.) · How many lamps, especially fluorescent and metal halide lamps. · What wattage? · Length of fluorescent lamps. · If metal halide, is it single-ended (mogul screw-in base) or double-ended? · Is your metal halide lamp rated for its burn position? Some metal halide lamps’ ID includes a ‘U’ for universal burn position – it can be placed in a horizontal or pendent fixture. Others are designed to operate in a given position (‘BU’ for base up’ or ‘BD’ – I’ve never seen one of those in an aquarium application!) · What spectrum? If LEDs, are they Royal Blue, Warm White, Red, etc. If metal halide, what Kelvin? If fluorescent lamps, what is the brand and trade name of the lamp (Brand X Super Actinic, Brand X Sunlight Plus, etc.) · If using LEDs, are they dimmable? · What sort of luminaire (fixture) will you use? This is especially important with metal halide lamps – pendent fixtures (with the lamp mounted base up) usually focuses light in a tight circular pattern resulting in higher light levels. · What sort of ballast will you use? Standard? Electronic? Some ballasts overdrive lamps thus creating more light (and possibly reducing the life of the lamp.) · How high will the luminaire be off the water surface? · What is the geometry of the luminaire. This is important! Narrow fixtures focus light and wide ones diffuse it. · What is the reflector material? Is it painted white? Brushed aluminum? Polished aluminum? Dimpled aluminum? Stainless steel? · Does the luminaire have a ‘splash guard’? What is it made of? Glass? Acrylic? · How old is the splash guard? If plastic, has it yellowed due to exposure to UV radiation or warped due to excessive heat? · Is the splash guard easily cleaned? Salt spray can cake upon a splash guard and reduce light transmission. · How is heat dissipated from the luminaire? Fluorescent tubes are designed to operate maximally at a given temperature. Temperature affects internal pressure, which, in turn, affects the quantity of light produced. · Is the luminaire simply vented, or is a fan used for cooling? · If a fan is used, can you easily monitor it for proper operation? Heat is the enemy of light production by fluorescent lamps and LEDs. · Is the luminaire housed within a hood? · If using lamps that produce a lot of heat (such as metal halides and, to a lesser degree, fluorescent lamps), how will you deal with possible heat transfer to the aquarium water (room air conditioner, chiller, etc.) · What sort of water moving devices will you use? Water surface agitation causes waves that can focus light in what most hobbyists call ‘glitter lines.’ Water motion can also affect the rate of photosynthesis. · Do you plan to monitor alkalinity? This parameter can influence the rate of photosynthesis. · Will you feed the corals? Feeding (heterotrophy) can lessen the coral’s reliance on ‘food’ provided by photosynthesis (phototrophy.) · What color will the corals be? Darkly colored corals (brown) absorb more heat than lightly colored ones. This can happen in an aquarium using lights that produce a lot of heat. · Are you willing to perform water changes (or use and maintain activated carbon) in order to minimize ‘yellowing’ of the water? Yellow water absorbs blue light thus reducing the amount of PAR available to the animals/plants. · If using fluorescent lamps, do you plan to turn them on and off several times a day (in an attempt to mimic daily natural light intensity patterns? Each on/off cycle damages the tube’s anode/cathode (called ‘sputtering’) and coats its internal surface with metal particles. This is most apparent as a black ring at the ends of the tube in old lamps.) Can you bear the expense of changing the lamps more often than generally recommended?