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250 Watt 20000K Metal Halide Bulb - German Radium, Mogul Base


Item #: MB6811

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The German-made Radium 20000K metal halide bulb offers excellent coloration and good intensity. It is crisp-white with a strong blue tint. It brings out the fluorescent pigments in corals nicely. Fluorescent supplementation is usually not necessary, but can be used for added intensity and to simulate dawn and dusk. An electronic ballast, magnetic pulse-start ballast or magnetic HQI ballast is required to ignite this bulb. This bulb is white with a blue tint on a magnetic HQI ballast. It will burn more blue on an electronic ballast or pulse-start ballast. An excellent choice for  reef tanks 22"–30" deep.

Common questions/problems concerning metal halide lamps:
  1. Metal halide lamps of the same kind are different colors?
    Metal halide lamps operate by passing an electric arc through an arc tube that excites particles in the arc tube. When the metal particles reach an excited state they emit energy in the form of visible light. It takes 100 hours of operation before the metal particles stabilize and become a consistent color. All metal halides require 100 hours of operation before color and light output stabilize. All metal halides inherently have a slight color variation between individual lamps.
  2. The metal halide lamp fires and then either burns dull or the arc extinguishes?
    Usually the ballast and lamp are not receiving enough power. Metal halides pull a high current. Usually the problem is either there is too great a load on the circuit or the extension cords are of a small wire size and can`t handle the power needed by the ballast. Use only heavy duty extension cords and try running a ballast off a circuit from another part of the house.
  3. Do I need a cover shield between the lamp and the aquarium?
    Metal halide lamps produce a large amount of UV and also have a potential of exploding. The single ended metal halide lamps have an outer jacket which eliminates most of the UV. However, they have an inherent risk of exploding and UL requires metal halide lamps to be enclosed. On double ended lamps there is no UV shield. Double ended lamps must have a glass shield or major eye injuries including blindness may occur.
  4. Can I operate a ballast and lamp together which are designed for different wattages?
    Each wattage lamp and ballast are designed together for optimal performance and safety. If you over drive the lamp it may explode and shorten the life of the ballast and lamps. If you under drive the lamp it will also shorten the life of both components and also may explode. Do not mix different type wattages of lamps and ballasts.
NOTE: The bulb should be handled carefully. Using soft gloves is a good idea to keep finger prints off bulb. This is during installation and replacement.

*Requires HQI ballast, electronic ballast or pulse start ballasts to work properly.

Bulb Replacement Guide
Bulb Types Life of Bulb*
Normal Output Fluorescent 6-12 months
Very High Output (VHO) 6-12 months
Power Compact (PC) 9-12 months
T5 High Output (T5HO) 9-18 months
Metal Halide 9-12 months
LED (non-moonlight) ~5 years (50,000 hours)
* Manufacturer Recommendations

Manufacturer information

Radium was founded in 1904 in Wipperfürth, situated abt. 40 km north-east from Cologne in the `Bergische Land`. Already a short time later the production of lamps with high-quality tungsten wires started here. Due to its know-how Radium advanced fast to one of the most important companies of the region and nowadays counts among one of the most experienced brand-name manufacturers of the lamp industry.

5 Stars


Reviewed on
March 05, 2018

Yes, I would recommend this.

Radium 250watt bulb

Pros: Beautiful spectrum of light it produces, quality made bulb

Cons: A bit pricey

Absolutely the best looking halide bulb out there. Produces a great spectrum of light and growth was good when used for a few years over 120 gallon mixed reef.

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Reviewed on
August 22, 2017

Yes, I would recommend this.

The only bulb worth buying

Pros: Great look and growth

I've been using these bulbs for years now and they work amazingly.

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brian alten

Reviewed on
July 01, 2016

Yes, I would recommend this.

As good as advertised

Running the 250w on an hi ballast, gives a nice crisp white/blue, very close to what I have with the Phoenix

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howard bladen

Reviewed on
May 29, 2014

Yes, I would recommend this.

Great bulb

Been using this bulb for the last 5 years on my 180 gallon with soft corals. Corals have been growing and I love the blue spectrum. I have 3 bulbs suspended about 18 inches above the tank.

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otis glamore

Reviewed on
May 07, 2014

Yes, I would recommend this.

ok bulb

This product is a fine one, if you can get one that isn't damaged. The first bulb was cracked or scratched, which means "DO NOT USE". The replacement unit was undamaged. What is especially nice is the color, which creates a very natural "blue" tint and really makes the colors of the corals and fish pop.

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tin dang

Reviewed on
April 21, 2014

Yes, I would recommend this.

400W Radium


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dennis erickson

Reviewed on
June 04, 2013

Yes, I would recommend this.

400 Watt Radium 20K

The 20000K bulbs are great, a lot more light then the 250 watt bulbs, but that also comes with more heat and the chiller has to work harder. The blue tint from the bulbs make the corals pop with more color.

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elton garcia

Reviewed on
April 07, 2013

Yes, I would recommend this.

radium 20k bulb

The bulb works great and gives off great shimmer. The corals seem to like it as there is great polyp extension.

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scott gregory

Reviewed on
March 04, 2013

Yes, I would recommend this.

Great Customer Service

Your service and follow up on my purchase was excellent. Have used these bulbs before and had downsized my tank but I am now back using these bulbs. I honestly forgot how nice they were. Thank you! I'll be back!

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eduardo hernandez

Reviewed on
December 27, 2012

No, I would not recommend this.

not a true 20K

Great price and good intensity but does not match up with my other bulbs.It has more of yellowish tone

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