MH bulbs and yellow color

[Anonymous]

Ok I bought a semi-cheap MH setup, it was a custom sea life dual 175W MH ballast, and came with 2 10000k bulbs. I just got the wires so finally got to test it. Only problem is it seems yellow(tried both). Now he claims that the bulbs were only 5 month old, so assuming that is true, the bulbs would not color shift that soon right? I thought they had a useful life of 12+ months?

Now removing the bulb age from the equation, I've read that some 10000k bulbs do have a yellowish color to them (crappy bulb maker perhaps?) so assuming that this came as a setup (bulbs original) did the CSL bulbs have this yellow to them? Maybe this is the issue.

Another thought is bulbs not having been used for a month or more, might have gone "bad" ?? or maybe they need to burn in a little more?? Is this a valid arguement?

Finally I did briefly see the bulb directly (yah I know bad idea, I can feel the tumors growing as we speak) and they did look bright white-bluish so perhaps it might be some algae growth in the tank that's causing this yellowish-green look? Although I'm sort of dismissing this fact because my 10000k PCs show up as bright white right to the rock, although who knows maybe the point source nature causes the light to spread out more due to algae (although a quick test over a tank with fresh water in it might clear this up).

Also in an off topic note, how important is it to completely enclose the front of the light with glass (and if so important, any thickness recommendation?), as I've heard that MH bulbs produce UV, including UV-C, and while I can block off stray light (direct line of sight) for myself with cardboard or something, I'm a tad worried about the fish and stuff in my tank. Right now there's an 18" wide glass brace down the middle of the tank, so directly below probably is safe, unfortunately I'm a tad worried about to the sides at an angle where it isn't protected by glass.

Ok here are some pictures of what I'm talking about, the first two are right in the center of the tank directly under the MH bulbs, the first is with the MH on (you can definately see the yellowish green), the second is with it off, in both cases there my PC lights are on (just to either side though).

MH on

MH off

Now a thought occured that the months that my tank has been up maybe some sort of algae grew on the rock (which it did), and since it wasn't being directly lit I couldn't really see it as much and now I can, so here's a shot to right which is directly under 2-55W 10000k PC bulbs, where the MH bulb is about 3 feet from the end of the tank so its shooting down at about a 45 degree angle.

MH on

MH off

 

[krullulon]

wow -- there are a lot of lighting discussions going on recently. :lol:

different bulbs have different spectral outputs, you can't always go by the "k" designation... it's a general guideline at best.

i had a ushio 250W 10k MH until recently, but it was too yellow for my tastes... so i switched to an XM 10k and the light is much more crisp white now. there's a ton of variation between manufacturers, and you can even note a difference sometimes from bulb to bulb.

http://www.cnidarianreef.com/lamps.cfm has an interesting comparison with photos of different MH bulbs -- you can see the variation here. if you know the manufacturer of your bulbs (it sounds like you don't) you can look-up their spectral output and see where the bulk of the light is focused (blue, red, yellow, etc.). most of the major bulb manufacturers will have this data on their web sites.

if your bulbs are single-ended (as i'm gathering from your post), then the outer glass shell probably has a built-in UV filter and nothing to worry about. double-ended MH bulbs typically don't have an outer shell, so adding additional UV protection is more important.

 

[Anonymous]

different bulbs have different spectral outputs, you can't always go by the "k" designation... it's a general guideline at best.

Yah I'm gathering that info slowly as I search online dealers for bulbs and seeing a bunch of 175W 10000K bulbs and seeing "yellowish" "bluish" "white" *sigh* I thought the whole idea of 10000k was to state the spectral output! I know what the blackbody of a 10000 kelvin object is, so why confuse me!

http://www.cnidarianreef.com/lamps.cfm has an interesting comparison with photos of different MH bulbs -- you can see the variation here. if you know the manufacturer of your bulbs (it sounds like you don't) you can look-up their spectral output and see where the bulk of the light is focused (blue, red, yellow, etc.).

Yah I don't know the maker, seems all mogul base bulbs look identical, with no commercial brand stamp or anything on it other than stamped at the top "MH 175W 10K" And unless custom sea life used a particular brand bulb with its setups before they went out of business (which I'm doubting) doesn't look like I'll know what bulb I have. But thanks for the reference I'll be sure to study it well.

if your bulbs are single-ended (as i'm gathering from your post), then the outer glass shell probably has a built-in UV filter and nothing to worry about. double-ended MH bulbs typically don't have an outer shell, so adding additional UV protection is more important.

Oooh now this is a breath of fresh air! (I can feel the tumors in my eyes receeding already! Yes I do have a single-ended bulb, screw in mogul type, but I didn't the glass covering it was particularlly UV blocking, but if it has a UV filter then whew.. I'm still going to make sure not to stare at the bulb, but atleast I dont have to worry about my fish getting tumors or sterilizing my live rock.

Btw, is there any concensus on how to place bulbs in a tank, perpendicular to the length or parallel? (with a reflector that is)

ie
xxxxxxxxxxxxxxxxx
x...........................x
x..***............***..x where the x is the tank outside, * is a bulb
x...........................x parallel
xxxxxxxxxxxxxxxxx

or

xxxxxxxxxxxxxxxxx
x....*................*...x
x....*................*...x perpendicular, obviously not ascii'd to scale.
x....*................*...x
xxxxxxxxxxxxxxxxx

 

[krullulon]

it depends on how much tank length the light needs to cover vs. how much tank width... the reflector will generally maximally disperse light along one axis depending on its orientation (unless you have some wacky parabola :lol: ), so if you need to cover more horizontal tank length you'd probably go with the bulb perpendicular (as in your second diagram) and the reflector distributing the light across the length of the tank. however, if you have multiple bulbs that make the length of the tank you need to cover with each bulb less than the width of the tank, it would make more sense to go parallel and have the reflectors distribute the light from front-to-back.

i have a 90g 36x24 with one 250W MH, so i have the bulb perpendicular to the length with the reflector distributing light along the 36". if i had a 2 MH bulbs, i'd flip the orientation because each one would only need to cover 18" of tank length, so i'd want my reflectors aligned with the the 24" front-to-back width to get the most punch.

 

[Anonymous]

Looks more like a 55K bulb. Get a new bulb. XM 10K or AB 10Ks are blue/white. Some say the 10K ushios are yellowish.

 

[Len]

Sometimes the obvious can be overlooked. If you're not using heavy skimming and carbon, try it first. 10,000K bulbs will really show tanins and other yellowing compounds that you didn't know was there before.

 

[Anonymous]

Len, yah I got that advise the other day, so I'm pulling out all those archaic whisper/penguin filters I'd never thought I'd use and run them with no sponge just a bag full of carbon

But still dont know the reason why the MH will show these things, but not PCs, perhaps its the point source nature of the MH?

 

[shawnz28]

The Ushio's I have seen always seemed very white to me personally. Right now I am running 2 250watt 10K hamiltons with actinic supplement and I am very happy with these bulbs after they burned in.