[gramesy777]

alright...im buying the bulbs for my metal halides and i dont really understand the 10000k or 20000k thing?? Whats the difference and which is better for me. Im running two 175 watt bulbs over a 45 gallon tank w/ actinic fluorescents

[WILLIAM1]

Kelvin Temperature & CRI
Metal Halide bulbs are rated in Kelvins. The 'K' stands for Kelvin (a measurement of temperature), and is a reference to what we perceive when we look at a heated black body (a star is a common example). The K rating in a lamp model is a form of addressing the color output of a lamp, also known as the Correlated Color Temperature (CCT). The hotter the Kelvin temperature gets, the bluer. Always choose a bulb with a kelvin rating that is at least 6500K for reef or planted aquariums. Kelvin ratings that are lower that this are going to emit a yellow light that is not visually appealing. 10k lamps have a nice crisp white, while higher Kelvin can go from a blue/white to very blue and lower Kelvin seem more like that of sunlight (6500k). Metal Halide aquarium bulbs go up to 20,000K providing the bluest light. See the chart below for more information.

The color rendering index (CRI) refers to the bulb's ability to render individual colors accurately. The higher the CRI the more natural and vibrant the colors will look. A bulb with a CRI of 85 or higher is excellent being that the sun has a CRI of 100. To give you the best color rendition (CRI rating) and bring out the natural beauty of aquarium fish and plants in both freshwater and marine tanks, choose a 6500K daylight bulb with a CRI of at least 85.

We carry only the highest quality metal halide lamps on the market from many different manufacturers such as Radium, Ushio & Eye Iwasaki insuring the lamp has been tested, and is represented accurately as color temperature. Eye Hortilux makes 90 - 92 CRI bulbs that are excellent for both planted and reef aquariums.

Kelvin Rating Chart

Kelvin Rating Description Uses Bulb Types
4000K Neutral white light General lighting, factories, parking lots, warehouses Metal Halide
T5 Fluorescent, T8, T12
5000K White - daylight General and retail lighting applications Metal Halide
T5 Fluorescent, T8, T12
6500K A high CCT white daylight source that looks the most like natural sunlight Aquariums, greenhouses, general office lighting
Used to simulate average outdoor light conditions Metal Halide
T5 Fluorescent, T8, T12
10,000K Crisp white light Aquariums & greenhouses Metal Halide
T5HO
20,000K Blue light Aquariums Metal Halide
T5HO

[WILLIAM1]

Aot of people like the 20000k bulbs becuase of thr blue light the bulb gives off. But I heard coral grow slower.

[gramesy777]

okay thanks for that info...what is best in my 45....i was thinking about using 10000k metal halides considering i have the actinic fluorescents...i dont want it too blue