Color of Lighting - Kelvin Temperature (FYI 0 K = -273 C = -460 F)
Our sun is a red star which provides the standard for aquarium lighting. As stars go, they exist in different colors. Look into the heavens on a clear night and you can actually see this. Very simply, the "cooler" stars are at the red/orange end of the spectrum while the "hot" stars are at the blue end. A more earthly example would be a propane torch's flame. The inner blue cone is hotter than the outer yellow cone.
Our sun is 5,500 Kelvin (9440 Fahrenheit) temperature = red/orange light
A blue star is 10,000 Kelvin (17,540 Fahrenheit) or more
Aquarium lamps come in Kelvin rated temperatures, recognize these?
5500 K = Requires lots and lots actinic (blue) lighting to color correct
6500 K = OK white color for reef aquariums, needs lots of actinic
10000 K = excellent white color for reef aquariums. Often actinic is added and recommended - simulates shallow water
14000/15000 K = more blue than white use with actinic for deeper water corals - best for the average coral tank
20000 K = very, very blue - requires adding white light to color correct. Very deep water simulation. Few corals live under this light.
Why Blue Light aka Actinic aka 7100K aka /03
Did you ever wonder why the ocean is blue? Hint: Water reflects blue light and our eyes only see reflected light.
When you light your aquarium, the water reflects blue as in the ocean. Our way of compensating for this phenomena is to include a blue light in your hood or canopy commonly called actinic (ack-tin-ic). A good ratio of actinic to white light is 60-75% blue : 40-25% white. In fluorescent lights, common white lighting is 6700 K while actinic lighting is 7100 K (with other colors removed so you see only blue). Together they let your tank inhabitants show their true colors. Turn off the blue light and the tank looks yellow.
To create various colors in fluorescent light, the interior coating of the tubes is changed. These coatings are called phosphors. Without out a phosphor coating, all bulbs would glow a soft, pale blue.
THERE IS A NEW 454nm ACTINIC OUT. LIGHT BLUE IN COLOR IT GOES WELL WITH THE OLD 460nm. IT BRIGHTENS THE TANK WHEN USED WITH ACTINIC-WHITES.
Metal Halide bulbs - starting for the first time
Brand new metal halide bulbs may take up to 15 minutes to start the very first time. Occassionally the bulbs go off - this is fine - let them set and they will restart. Let them run an hour before turning them off. It will also take 2 or 3 days of operating 6-7 hours to establish the correct color. So if it looks yellow in the beginning, be patient. Sometimes the center tab in the socket doesn't make contact with a new bulb. UNPLUG THE BALLAST, then pull it out ever so slightly. Retry your new bulb before calling me. - For you electricians out there - it won't light if it isn't plugged in.
WARNING - IF ADDING METAL HALIDES TO A CORAL TANK FOR THE FIRST TIME - START WITH 1 HOUR MAX OF LIGHT. YOU WILL BURN YOUR CORALS AND PROBABLY KILL THEM WITH THE SHOCK. Set timers to come on for 3 - 15 minute intervals to start. Increase slowly. Watch your corals, they will tell you how you are doing.
I am going to do my best to simplify lighting such that you will know how to make a well informed decision when it comes to your saltwater tank.
Metal Halide - the short, round, very bright bulbs
Metal halide lighting follows the same color/Kelvin rating system as fluorescent lighting (the long, skinny tubes). The major difference is in heat output and intensity or lumens. Given two bulbs of equal watts
Metal halide = very bright and very hot (+1000 degrees in the center)
Fluorescent = not near as bright but much cooler (much less than 100 degrees)
These are the two most important consideration when choosing your lighting system and when deciding what type of aquarium you would like to have. The brighter the lights the more corals you can grow (up to a point.)
Here's a very brief rundown on lamp types for the curious:
Electric lamps can be divided into incandescent (conventional and quartz-halogen) and discharge. Incandescent lamps (of either variety) put most of their energy out in the infrared, and so are of little interest here (think of them as tiny expensive electric space heaters that happen to light up).
Discharge lamps include fluorescent, mercury, metal-halide, low-pressure sodium, and high-pressure sodium. They all produce light by passing a current through a gas, exciting the odd electron here and there. The electrons emit light as the return to their ground state, and this directly or indirectly is the source of the illumination.
Fluorescent lamps use low-pressure mercury, which emits primarily up in the ultraviolet, and (except for blacklight and germicidal lamps) fluorescent's are coated internally with phosphors that glow under ultraviolet. The visible light they produce is almost all from these phosphors. Some types of fluorescent's make excellent light sources for aquariums.
Mercury lamps increase the pressure, which shifts more of the direct output into blue and green emission lines (these can be supplemented with phosphors to produce better color rendering); these are the blue-green lights you see illuminating parking lots and the like.
Metal-halide lamps introduce metal halides into the mercury lamp; this adds all sorts of nice emission lines to the spectrum, and greatly improves color rendition.
Low-pressure sodium lamps are not seen much, at least in the United States. They are the most efficient light source, because they put almost all their energy into one yellow-orange emission line (and the human eye is pretty sensitive there). Unfortunately, you can't see colors under this illumination; everything looks like shades of grey illuminated by a fairly ghastly yellow light.
High-pressure sodium lights are very widely used in the United States for street-lighting. If it is bright, kind of yellow with purple overtones, and you can pretty much distinguish color under it, it is high-pressure sodium. GE, at least, has some "white" sodium lamps that actually render colors fairly well (but nowhere near as well as MH or fluorescent), so perhaps someday these will make reasonable light sources for tanks (but I don't think "someday" is today).
Lighting and What Really Matters
T5 vs PC vs VHO (T12)
Before you buy lighting, know what you are buying. The original and still the best is the T12 VHO lighting.
let's compare bulbs for a 4 foot tank.
TYPE VHO POWER COMPACT T-5
Length 48 OR 46.5” ~34” 44”
Watts 110 96 (twin 38w tubes) 54
Diameter m 1.5” 7/8” or 5/8” 5/8”
Pins bi-pin 4-pin bi-pin
square or straight narrow
COST EA. $35 $45 $34