Understanding Radium Metal Halide Lamps


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.

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