Reef Corner Newsletter
Each newsletter will introduce a new specimen, picture of the week and provide a technical article on some aspect of reef keeping.
Picture of the week
Blue-Spotted Watchman Goby
Cryptocentrus pavoninoides
Topic: Lighting
Part 1: The Basics of Metal Halide Lamp Technology - Terminology
This article is an introduction to the terminology used when discussing metal halide lighting commonly used to light reef aquaria.
Arc Tube – Sealed quarts tube where the electrical discharge (arc) occurs. The arc tube contains electrodes and various compounds such as mercury and metal halides which when ignited cause the lamp to glow with the desired light.
Ballast –Magnetic or electronic circuits that are designed to operate metal halide lamps correctly. Most metal halide lamps use a remotely mounted ballast which is positioned away from the hood.
Base – The end of the lamp that inserts into the lamp socket and makes electrical contact. There are a number of types of bases in use, but most common single-ended reef aquaria MH lights use what is known as the Mogul base
Burning Position – Denotes the correct orientation the lamp should be in while operating. Most lamps used over reef aquaria are designed to burn in the horizontal position.
Color Temperature – The color of the ‘white’ light given off by a lamp is called the ‘color temperature’. The unit of measurement is the Kelvin, abbreviated K. The higher the color temperature, the cooler (bluer) the light appears. Incandescent lights are approximately 2800K, cool white fluorescents are about 4100K, daylight fluorescents are about 5000K. The sun is generally considered to be in the 5000K to 6500K range depending on atmospheric conditions. Metal Halide lights used in reef aquaria range from about 5500K to 20000K. The higher color temperatures are approximations as the color is no longer ‘white’ and it is impossible to measure the color temperature of these lamps with any exactness.
Color Rendering Index (CRI) – A measure of the quality of the light. It is a measure of the lamps ability to ‘render’ colors accurately. This is in relation to how the colors look under natural sunlight. A CRI of 100 indicates that the light exactly duplicates the colors of natural sunlight. All artificial lighting creates light with a CRI of less than 100. A CRI in the range of 90-95 is generally considered excellent.
Envelope – Outer glass bulb designed to maintain a controlled atmosphere surrounding the arc tube and help contain most of the UV radiation emitted from the arc tube.
Frame – In a single-ended lamp, the lamp frame holds the arc tube in a specified location inside of the lamp outer envelope and provides an electrical path from the base to the electrodes inside the arc tube. Double-ended HQI Lamps do not have a frame.
High Intensity Discharge Lamp (HID) – Indicates the family of lamps which include metal halide as well as mercury vapor and high pressure sodium lamps.
Hot Restrike - Attempting to re-ignite a hot lamp due to power cycling is called a hot restrike. Most lamps have a cool-down period before they will restrike, typically about 15 minutes.
HQI – Defines a type of MH lamp. HQI lamps generally are double-ended and have the best brightness and color performance, but they require ancillary UV filters to prevent UV damage to corals since they do not include an external UV absorbing envelope..
Lamp – This is the technical term for the actual light producing part of the light bulb.
Lumens – A measurement of lighting intensity.
Metal Halide Lamp (MH) – A high-intensity discharge light source in which the light is produced by the radiation from mercury together with halides of metals such as sodium and scandium which are excited by an electrical arc contained in an arc tube.
Mogul Base (MOG) – Indicates the standard screw-in type base found on single-ended metal halide lamps. It is similar to, but larger than, a standard incandescent lamp base.
Photosynthetic Available ( Active) Radiation (PAR) – PAR is a measurement of the intensity of the light spectrum that is specifically utilized by photosynthetic animals in the reef tank.
Ultraviolet Light (UV) - Ultraviolet light is invisible light at the blue end of the lighting spectrum. It is the the light responsible for causing sun tans and sun burns. All MH lighting some amount of UV light. Having some UV reproduces natural sunlight better. Having too much UV can cause damage to the corals.
Watts (W) – The power consumption of a lamp. From a system standpoint, the power consumed by the ballast due to inefficiencies must be added to determine the total system wattage.
Specimen of the week
Fungia / Disk Coral
Close-up view of the side showing the septa and polyps
This specimen is located in a moderate current location on the sand in a 24" deep tank under 400W 10K metal halides supplemented with VHO actinic fluorescent bulbs.
Its bright pink coloration has almost all occurred since placing this specimen in these conditions 6 weeks ago. It is believed to be a Fungia fungites
Scientific
Name: Fungia sp.
Classification: LPS
Description:
Forms flattened, normally rounded discs which contain a single polyp. The
disk may be raised in the center. Color may be brown, green, red or pink
often with a pink mouth or pink stripes or edging.
Veron: Corals are usually solitary, generally free-living except for juveniles, flat or dome-shaped, and circular or elongate in outline, with a central mouth. Septa have large or small, rounded to pointed teeth. Costae consist mostly of rows of spines. The skeleton often has pits between the costae on the lower surface. Tentacles may be extended during the and are short and widely spaced.
Natural Environment:
Veron: Reef slopes and lagoons on sandy,
gravel or coral rubble substrates.
Care:
Hardiness: Fungia corals are fairly hardy
corals when given the proper conditions..
Lighting:
Prefers bright lighting, may tolerate moderate lighting.
The coloration improvement in the specimen above appears to be related to
increased illumination. This specimen is kept under 400W 10K MHs.
Water Current: Prefers moderate water motion.
Temperature: Does well within a range of at least 78º to 82º F
Aggressiveness: Fungia corals have a fairly powerful sting, but fairly short tentacles. They do have the ability to move around a bit on the substrate and may need to be corralled in using small rocks.
Feeding: Fungia are photosynthetic and do not require feeding, but they will take small foods such as brine shrimp especially if offered in the evening or at night when the tentacles are extended for feeding.
Supplements: Maintaining correct calcium and alkalinity levels is undoubtedly important for skeletal development
Tank Positioning: Best positioning is on the substrate in a moderate water flow, but brightly lit area of the tank.
Reproduction: Young specimens sometimes bud off from the parent disk in the reef tank.
Note: Specimen identification and natural habitat Veron (2000)
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