Understanding Radium Metal Halide Lamps
 

With the recent surge in hobbyists transitioning back to metal halide lighting I have received many questions, and have come across all sorts of misinformation that has been given in regards to what has become far and away the most popular metal halide bulb to date, the Radium “20k”.

I would like to start this by stating the “20k” label, or 20,000*kelvin as it is implying, is nothing more than a color temperature that we hobbyists have labeled this lamp. Radium GmbH, the manufacturer of this lamp, labels this as a Radium “B”, where “B” means Blue. There is no implied actual kelvin rating from the manufacturer.

Radium metal halide lamps were first introduced into the North American market in late 1999, early 2000, by PFO Lighting. Prior to this lamp making it’s way to the market here we only had one other metal halide lamp that was weighted towards the blue side of the color range, this being the Sun Burst 12,000k lamp which was slightly more white in appearance when compared to the Radium Blue lamp. Because of this look, us hobbyists dubbed the term “20,000k” or “20k” for the Radium.

Radium 20k metal halide lamps are offered in four different wattage and base configurations. These are as follows:

150w Double Ended
250w Mogul Base
400w Mogul Base
1000w Mogul Base

Following is the pertinent information for each specific lamp from Radium, excluding the 1000w that is rarely used in our hobby.

150w Double Ended

The 150w Double Ended Radium is a bit of a different animals in terms of visual color than the three mogul base wattage offerings. This lamp runs substantially more white in appearance, and doesn’t provide the same “color pop” that the higher wattage mogul base lamps provide. Due to this the 150w lamp does not have the same hobbyist following and popularity that the mogul based lamps have. The specs for the 150w are as follows:

Lamp Wattage: 150w
Ballast Spec: ANSI Code M81 Magnetic HQI
M81 Magnetic Wattage: 172w
Luxcore Electronic Wattage: 148w
Average Lamp Life: 10-11 months @ 8hrs/day

250w Mogul Base

The 250w Mogul Base Radium is a unique lamp in that it’s actually rated as a 270w lamp and is specified to be ran off of an M80 Magnetic HQI ballast. This is one of the very few metal halide lamps on the market which are single ended that are spec’d for this particular ballast. This does not mean that the lamp can only be ran off of a magnetic M80 HQI ballast though. Other ballasts that are very common to run this lamp with are standard electronic ballasts such as the ReefBrite, old IceCap, or the Vertex ballast. With the introduction of the somewhat new “Select-a-watt” ballasts that are now on the market such as Lumatek, and even better the Luxcore brand, you can choose to run this lamp at standard 250w, closer to spec of 270w with the “250” or “250 HQI” settings that are on these select-a-watt ballasts.

When running the lamp off of a magnetic M80 HQI ballast you will pump a good amount more of white light through the lamp, which is easier to see with the naked eye. This is the result of the lamp running at a slightly higher than intended wattage, at 330w. Please note that actual wattage to the lamp will be slightly less due to power loss through the wiring. This makes the lamp have a very good mix of white and blue light, and excellent PAR numbers for a bulb that is heavier weighted to blue side of the spectrum.

Running the lamp on the standard electronic 250w ballasts will produce the most blue out of the lamp that you can get. The wattage does drop down on the lamp to approximately 245w, and the more visual white light is more subdued to the naked eye. PAR levels do decrease, but you do gain some in terms of coral coloration that is displayed.

When using an electronic ballast that has a select-a-watt setting on it and running it on the “250 HQI” you split the difference in output between a standard electronic 250w setting and the magnetic M80 HQI numbers. This gives a very good balance of blue and white mix to the lamp, and splits the difference between PAR numbers that generally equate to growth, and more blue light, which usually helps with maximum coral coloration.

250w specs are as follows:

Lamp Wattage: 270w
Ballast Spec: ANSI Code M80 Magnet HQI
M80 Magnetic Wattage: 330w
Electronic 250w Setting: 245w
Electronic 250w “HQI” or Super Lumens: 300w
Average Lamp Life: 9-10 months @ 8hrs/day

400w Mogul Base

The 400w Mogul Base Radium lamp is actually a 360w metal halide lamp that, just like it’s 250w counterpart, needs a ballast with an igniter to fire properly – such as an HQI or Pulse Start ballast. The downside to the 400w Radium is that the actual spec ballast for this overseas in 230v does not exist in North America in 110v-120v. Because of this when the lamp was first imported PFO figured out that the magnetic 430w Son Agro ballast (ANSI S145 – S51) would provide the correct voltage at start-up to the lamp to fire it properly. However, this PFO 400w “HQI” ballast as it was dubbed just so happened to overdrive the lamp to the tune of approximately 470w. The upside of this was an unmatched combination of PAR and blue light that had never been seen before giving an amazing combination of both growth and color with corals, specifically SPS. The downside of this was the bulb was being overdriven so much that the average spectral life usually hovers between 6 and 7 months. However, the positives of the light produced with this combination have far outweighed the early spectral shift from being overdriven for most.

Unfortunately the 430 Son Agro ballast is no longer manufactured, however there seem to be a few other spin off ballast manufacturers that make a very similarly spec’d magnetic bare ballast and capacitor for those DIY’ers out there. This leads into the electronic ballasts that are available on the market now that have standard 400w settings on them, as well as the select-a-watt ballasts which have the 400w “Super Lumens” or “HQI” setting on them.

The 400w standard electronic ballasts, or setting on the select-a-watt do run the lamp closer to the rated spec of 360w, with a rating of 425w. This does have a significant impact on the PAR of the lamp though, reducing by approximately 30%. This does however increase the visible blue light that you’re seeing with the naked eye, and has a fairly large impact on the color displayed by the corals. In situations where this lamp is being used more for color than it is growth, this would be the optimal way to run the lamp. Spectral life of the 400w lamp is at maximum with running the lamp at this wattage, getting right up to 8 months out of it.

The 400w electronic ballasts running the select-a-watt setting on 400w Super Lumens or HQI split the difference between the old magnetic 400w HQI ballast and the electronic ballast setting. Color is a good mix of both blue and white, and gives a very good combination of both growth and coloration. The wattage rating to the lamp does go up to 450w, thus decreasing that spectral life to around 7+ months. This is a great ballast and setting alternative to those who cannot track down the old style magnetic 400w HQI ballast that both PFO and Sunlight Supply used years ago. **Please note that Hamilton Technology sells a 400w “HQI” magnetic ballast. This is NOT the same ballast as the 430 Son Agro that was inside the PFO HQI and Sunlight Supply HQI. **

400w Specs are as follows:

Lamp Wattage: 360w
Ballast Spec: True European 230v HQI Ballast – Not available in US
PFO HQI (Son Agro 430) Wattage: 470w
Electronic 400w Setting: 425w
Electronic 400w “HQI” Or Super Lumens: 450w
Average Lamp Life: 6-8 months @ 8hrs/day

I hope this helps anyone who is specifically looking to run the Radium metal halide lamps and selecting the correct ballast for their particular application and needs with this setup.

Great info! Thank you for clearing up questions about this bulb.

CR

Hey Jeremy,

Is anyone currently manufacturing the M80 magnetic HQI ballasts?

Yes, both Hamilton Technology and AquaMedic still produce a 250w M80 ballast.

Great info Jeremy!!!! Long live MH!!!!

Jeremy, say using a Select-a-watt like Luxcore on 250MH if I have it on "Super Lumens" does it shorten the life of the Radium significantly or not really at all? I would think a little but just wanted to hear it from you :)

CR

Fantastic info! Hamilton should remove the HQI label on the M135, it totally threw me off the other day when we talked. Like the new Avatar!

The Super Lumens setting will have little impact, if any at all, on the spectral life of the 250w lamp. On the 400w lamp that is not the case the though.

Great thread. Thanks for posting

Sticky this!

Hi Jermey.

I may be in the market for 400W metal halide ballasts in a few months to run the Radium B 400W bulbs in a blank Geismann Spectra 72" fixture.

It seems according to your website - all that is available is the Luxcore model supplied by Coralvue. Would this cover the requirements outlined here: "The 400w electronic ballasts running the select-a-watt setting on 400w Super Lumens or HQI"

Oh yea - I know nothing about Metal halides so your descriptions above are quite helpful.

Thanks!

I run a comparable ballast on the "HQI" setting by Lumatek to drive a 400W Radium. It's a fantastic combo. I'm sure Jeremy can concur.

Thanks for this! I am planning on a 400w Radium bulb for my 150g DD and needed some info.

A select-a-watt ballast such as the Luxcore would get you the closest to the operating specs of the old "400w HQI" ballast. As loweryster pointed out it's a great combo to run if you don't have that old 400w HQI ballast.

If we had the oppurtunity to set up a 240V circuit - what would be the ballast reccomendations for the radium 400W?

If you could find it the ballast would be a 230v 360w ballast that would have the specs of an M165, but the ignition voltage between 4kV and 5kv. This is going to run the lamp fairly dim and blue compared to anything we've ever ran it off of here in the US.

The thing we have to be careful of is that over there, if I remember correctly, the power is 50Hz, we are 60Hz here. So a ballast designed for 220v there, wouldn't likely work properly here.

Don

Correct, you can not operate 50Hz products in 230v here in the US because of us being 60Hz cycling here. If I'm not mistaken the only way possibly to safely do this is to use a VERY expensive step up or step down transformer to handle it?

Thank you for this post it's great info!!
I have a 36" x 20" x 21" rimless tank. 90% sps. Will I be able to run one 250W? If so suggestions on fixture please. Thanks again

Thanks Jeremy !! Great info !!

I have pretty much the same size tank and have been looking into it also. There are a few sps tank ive seen that run one 250w over a 36" tank and look to be fine but i still going to go with two 250w just to get the best coverage.

I agree with Albert, if I were doing a 250 on a 36" tank I would try and do two. Having said that I think that a single 400w would work pretty well too, but the overall coverage still wouldn't be as good as 2 x 250's. The aquascaping of the tank will play a big part in this as well. If it's a very open aquascape with the majority of the corals to the center of the tank and not stretched out to the end panels, then a single 250 could be more than plenty for you.

I run my three on icecap 400 watt electronic ballast that I've had for 7 or so years. Does that run it St 360 watts as well?

I apologize in advance as it is not my intention to hijack your thread, but I am considering my lighting options for a 180 I'm getting ready to start building. One thing that makes it hard to just jump on board with one lighting technology vs another is not really understanding all the in's and out's of each. I feel I've gotten to a point where I'm fairly comfortable with everything but metal halide lighting though and I cannot seem to be able to find my answers elsewhere. The question I have at the forefront of my mind right now is how to reduce the complexity of design and improve efficiency. Is it possible to power multiple lamps off of a single ballast by running them in series as you would LED or T5HO? If this is too off topic please let me know and maybe you can just send me in the right direction. Thank you

An older IceCap ballast should run that lamp right around 400w or just slightly over.