For marine aquarists in Hampton Roads and beyond!

10k, 14k, or 20k?

27 replies [Last post]
Mikeskillz
Mikeskillz's picture
User offline. Last seen 1 year 28 weeks ago. Offline
Joined: 04/18/2009
Points: 928

Does anybody know what the difference between 10k, 14k, or 20k metal halide bulbs? I have heard that the 14k and 20k give off more of a blue color and that 10k bulbs are good for growing coral but I was wondering which bulb would be the best choice to keep the coral in my tank looking and growing good. I read on a Coral farm website that 20k was the best but other sites say different. Does anybody have experience with these different light temps? I am going to buy new bulbs but I don't know which ones to get. Thanks a lot.

A hobby is something you do in your spare time, but your passion is doing something you love.

Woody (not verified)
What "color" do you like

What "color" do you like best? Some people like more of a blue color (20k) and some a blue/white (14k). The lower you go in the spectrum, the more yellow the color gets. I'd choose according to what's pleasing to your eye. You're the one having to look at it Smile

geminianspark
geminianspark's picture
User offline. Last seen 4 years 22 weeks ago. Offline
Joined: 05/20/2009
Points: 87
From what I understand it's a

From what I understand it's a personal preference thing.

Personally, I have a 14k on one side of my tank and although i do enjoy the vivid-ness of it, my probs are that "to me" my purple colored corals look more pink which i don't like. And I seem to have more nusicense algae on that side of the tank. I've been playing with water flow as that may be the cause and not the bulb spectrum but i'm trying to rule out everything but the bulb cuz the amount of algae that grows on that side of the tank is very prominent compared to the other side of the tank.

On the other side, I'm pretty sure I have a 20k bulb. It puts out a decent amount of light but it's not as reflective and bright as the 14k. It has a VERY blue look to things almost like having a strong actinic on. No where near as much algae but it just doesn't produce that shimmer that the 14k provides.

These are just from personal experience and my opinion only. My suggestion if you can afford it, is to buy one of each. Try them out for a month or two and pay attention to not only the color you see but the amount of coral growth and algae. I'd like to try out a 10k just to see if it washes out the colors as bad as I think. But overall... i think i like the 20k.

Mikeskillz
Mikeskillz's picture
User offline. Last seen 1 year 28 weeks ago. Offline
Joined: 04/18/2009
Points: 928
I have 10k bulbs in right now

I have 10k bulbs in right now and it looks bright but the color of the corals is really dull. I bought my light fixture used so I think the bulbs are pretty old. I think I might give the 14k's a try and see how they work. Does anybody know if the different temps affect the corals in any way?

A hobby is something you do in your spare time, but your passion is doing something you love.

geminianspark
geminianspark's picture
User offline. Last seen 4 years 22 weeks ago. Offline
Joined: 05/20/2009
Points: 87
from what i've read... 10k is

from what i've read... 10k is for growth, 20k is for color and 14k is supposed to be somewhere in between. I also read that there is a 15k bulb out there for people who like a little more blue than the 14k offers.

Patrick
Patrick's picture
User offline. Last seen 3 years 22 weeks ago. Offline
Joined: 04/16/2009
Points: 473
I do not have time now as I

I do not have time now as I am off to look at a house right on the coast, but I will get to this this evening. 12 to 20 Ks are my favorites with 14 being most.

The enemy of good enough is better.

dkoernert
dkoernert's picture
User offline. Last seen 7 years 17 weeks ago. Offline
Joined: 04/17/2009
Points: 139
Here is a question ( I

Here is a question ( I apologize for hijacking but its easier than starting a new thread). If I want to go from my current 150W 14k to a 150W reeflux 10k (for better growth), should I screen the tank for a few days/weeks?

c.talecki
c.talecki's picture
User offline. Last seen 5 years 18 weeks ago. Offline
Joined: 04/17/2009
Points: 999
screen -

I wouldn't worry too much, since you are just changing the spectrum - provided that the bulbs you are changing are not old enough that they've lost a majority of the intensity.

But if you are worried about it you can raise the lights up a bit and make sure to change the lights at night after they go off. That way when the lights come on the next morning the corals can acclimate to them better then if you change them in the middle of the day.

Some corals may be mad for a few hours, but they should adjust shortly there after.

Fill your tank with $5 bills, pour some gas in, light it on fire.......then you'll know the real cost of reefing.

dkoernert
dkoernert's picture
User offline. Last seen 7 years 17 weeks ago. Offline
Joined: 04/17/2009
Points: 139
That is what I figured, I'll

That is what I figured, I'll just have to be careful. Im either going 10k or 20k (total opposites of course), still have yet to decide. I have just always heard that the change to a "whiter" light can result in a lot of problems.

Patrick
Patrick's picture
User offline. Last seen 3 years 22 weeks ago. Offline
Joined: 04/16/2009
Points: 473
Bulbs, bulbs, bulbs......

There are a great many myths about lighting. One color supposedly gives the best growth, one brings out the best colors, and some have even put forth that you can only keep some types of corals under one color of bulb. These statements all have some merit of truth to them. But, none of them is accurate completely by themselves as stand alone statements, nor can be succinctly adapted to a universal truth by aquarists as many too often do.

First, what the "K" in the bulb rating means.....
As one gathers from the term “metal” halide....there is metal in the bulb......specifically in the form of pressurized gas. Argon and mercury are staples in the bulbs we use and there are different mixtures and percentages of argon and mercury as well as other halide metals inside the globes of the bulbs. There are also some bulbs that use sodium, but these almost always tend to give off yellow spectrums that just make aquariums look terrible, but they could be used and probably well. They are most popular among the plant growers. Use of sodium halides over your tank could make it look like a urine bottle. All in all, the “mixtures” of the metals are what ultimately determine the K rating and the color temperature of the bulb. When electric current is arced across the filament, it causes the metal gases to heat up and “burn”. You may have noticed this occur when the bulb starts up.......in the manner in which it takes up to a minute or two to get bright. The 10K, 12K, 20K (really should be correctly listed as 10000K, 12000K and 20000K respectively) is the temperature (in kelvin) at which the bulb reaches in order for the metal filament to burn at its running peak.

When these metals “burn”, they release photons......which is a fancy term for describing the energy released when electrons escape their orbitals from the metals as they get so hot (lots of added energy to the electrons with this heat so they spin much much faster) that their nucleus no longer has the pull to hold the outer electrons in their orbitals. Anyway, if the bulbs do not reach the correct temperature, they do not release the photons as they are rated for. This is the main reason you cannot use a bulb with one rating with a ballast of another rating. You will either not get enough current to run the bulb or you will run too much current and fry the bulb.....if not start a fire.

Back to the gases......
What gases, their percentages and what operating pressure they are under inside the globe of the bulb, truly determines at what color temperature one will get from the metal gases inside. Also, it normally takes about 100 burn hours before the bulb is emitting the spectrum for which it is rated. Because the gases that burn at 20000K tend to emit photons with wavelengths in the shorter, bluer end of the color spectrum, we just associate them with the color blue. Likewise, 6500K bulbs tend to emit photons with longer wavelengths and look more red or yellow. It would be really great here if I had the time and inclination to create some spectrum charts to show you what I am talking about, but these can be easily obtained on the web I am sure. The florescent bulbs I use here are nice enough to display the color spectrum of the bulbs on the box so I can see the peaks and pick accordingly. They work under a similar principle, but of course, differently. In any event, bulbs of 12000K mix the best of both ends of the spectrum and allow for a good mix. Mixed reefs tend to do well with these bulbs too and I will get to why in the next paragraph.

As for growth of a coral and color morphing......
Which spectrum is best for which coral really depends on the zooxanthellae and which spectrum they absorb best. Not every coral absorbs light the same way and therefore not every coral will grow “best” under the same spectrum of light. Corals that come from deeper water will likely grow best under light with shorter wavelengths and corals from shallow water will likely grow best with light that has longer wavelengths. The colors that corals attain has much to do with light absorption......and protection. UV radiation can “sunburn” corals too.....and MHs do emit UV radiation. The colors that zooxanthellae take on allow them to absorb light in the spectrum they are exposed too and the pigments also protect them from the Sun’s UV radiation. Many of us have seen where we get a coral in and place it in our tanks and it literally changes colors on us. Sometimes it is bleaching because the coral is sunburned and dies, underlit or lit with light that does not support photosynthesis, or it just changes colors to accommodate the new found spectrum of light you have offered it and continues to grow and do well......just with a different color than you thought you would have. Hopefully, you now have some understanding of why that happens. I like to use 12000K bulbs because I think they mix it up enough to offer spectrums for the broadest range of corals.

As to which bulb and color temp is “best”......that really is for you to decide. If you want growth most of all and have mostly SPS, then a 6500-10000K bulb will often allow folks to achieve the results they are after. The same cannot be universally stated though for other corals.......again it has to do with the coral and its zooxanthellae. The reason it is so often true for many SPS is because they quite often get collected in rather shallow waters......where they tend to grow. Softies and LPS many times are found a little deeper and get their max benefit from a bluer spectrum. In the end, take inventory of what you have, what you plan to have and take your best guess at which bulb is the “best”.

The enemy of good enough is better.

Patrick
Patrick's picture
User offline. Last seen 3 years 22 weeks ago. Offline
Joined: 04/16/2009
Points: 473
As for the other

As for the other questions.....

The reason that changing bulbs can often have a negative effect on some corals is that the light emitted from new bulbs often varies from the bulbs rating. As stated above, it can take several burn hours before the bulb is at the spectrum (color temp) for which it is rated. Also, it may never be exactly what it is rated for.....there is always a fudge factor and variances. Raising the bulbs or screening the light is never harmful but I personally have never done it and I have never had any issues. I would certainly never advise against these protective measures.

The enemy of good enough is better.