Lights: What's the deal with deg K?

[kris walker]

Hi everyone,
I have been pondering this question for some time now. One of my books explains the degree Kelvin rating for a bulb, and it says that the higher the rating, the more the spectrum goes towards the blue. The book says that actinic is around 7000 K, and normal whiter daylight is around 5000-6000 K. But I often hear about bulbs being 10,000 K or even 20,000 K and they emit white light! So where am I confused?
I am starting to think that the degree Kelvin rating is somewhat related to spectrum, but also related to power output from the bulb. Can anyone verify this or set me straight?
Thanks,
sam

 

[q]

Well let me see. The 6500K bulb does get some complaints for being yellow and the 10000K bulb is considered white and then the higher the number goes the more blue there is.
It is deffinatly related to spectrum. The higher K bulbs filter out the red, yellow and white colors leaving the blue. Remember how one of the causes of red sime can be caused by old bulbs. That is because as the bulbs age the spectrum shifts towards the red.
As a result the amount of light produced is less. How much? That is still not clear to me. It is true that the lux is lower on higher K bulbs but the blue spectrum in what is used in the corals. PAR measures the photosynthetic light that can be used by corals. For example Dr. Mac uses 400W 20K bulbs for his tank. They have a lower measurement of light output but yet still give better color than 250W bulbs that put out more light.
I hope Adrian chimes in on this one he knows his lights.

 

[kelly]

Surfin Sam,
You are partially right, it is related to the color spectrum, but not to power output. Color Temperature is a measurement in Degrees Kelvin that indicates the hue of a specific type of light source. Now what is Kelvin?
So, why do we measure the hue of the light as a "temperature"? This was started in the late 1800s, when the British physicist William Kelvin heated a block of carbon. It glowed in the heat, producing a range of different colors at different temperatures.
The black cube first produced a dim red light, increasing to a brighter yellow as the temperature went up, and eventually produced a bright blue-white glow at the highest temperatures.
In his honor, Color Temperatures are measured in degrees Kelvin, which are a variation on Centigrade degrees. Instead of starting at the temperature water freezes, the Kelvin scale starts at "absolute zero," which is -273 Centigrade.
Color temperatures attributed to different types of lights are correlated based on visible colors matching a standard black body, and are not the actual temperature at which a filament burns.
This is why you can have a 40 watt light that has a kelvin rating or 10,000k or even 20,000k. The higher the kelvin rating, the brighter white the light appears to the human eye. Now the tricky part comes in to play what is the best kelvin rating for the corals which you wish to keep. The actinic lights help with symbiotic algae, having a rating of around 7000-8000k.
Now I wish we could have a discussion the would help each of us know what the proper kelvin rating for each coral is. I have found the 10,000K bulbs have always worked well for me, but I have not taken the opportunity to work with 20,000k bulbs ye
This information taken from http://www.3du.com/library/colortemp.htm with additional comments.
Kelly

 

[adrian]

Q, thanks for the vote of confidence I guess you tend to learn a little when you own 10 MH and several florescents
Sam, Like Q said, the kelvin temp is directly related to the spectrum a certain bulb burns. One thing you have to be cautious about when talking Kelvin temp is that some manufactures tend to just "throw" a kelvin rating on their bulbs, and the spectrrum that is put off by a particular bulb can be quite different from the stated K temp. PAR is usually used when refering to intensity, most lower kelvin bulbs have a higer PAR than bulbs with higher K temps, although bulbs like the 1Ok made by ushio have a PAR rating thats right up there with the 65k made by iwasaki. As far as I know actinic bulbs do not have a kelvin temp, I think there is another kind of unit used to measure their spectrum, but I could be wrong A 7000k bulb would have a white/yellow color. Its said that the spectrum of sunlight at noon on a shallow reef would be right around 55k, a yellow/white color. Its true that corals use the blue end of the spectrum in photosynthesis, but just because you have say a 65K with a white/yellow color does not mean that the blue part of the spectrum is absent, there's just less of it. This is a pretty good rule of thumb when it comes to Kelvin temp, 55K yellow-white, 65K white yellow, 10K crisp white, 12-14k white with a little blue, 20K pretty darn blue. The actinic aspect of lighting mostly comes into play with deeper water corals, 20K bulbs are supposed to mimic the blue spectrum of sunlight once it penetrates deeper waters, you can run a healthy reef just using 55K bulbs with no actinics, but then you would have a tank with a yellow tint which most hobbyists dont like, although I kind like the look of a tank with less actinic supplementation, gives the corals and fish a more natural look. Of course most people like their tanks really blue causing the florescence of the corals and fish to glow. Which book are you refering to? Natural Reef Aquariums has a great write up on lighting and spectrum. HTH

 

[garyfla]

Hi
great discussion on lighting.Gained more than all the books I've read
I'm curious if anyone has checked out the
fluorex type bulbs? According to the hype on
the box:
500 watt output,consumes 65
8255 lumens of output super white
Unfortuneately the only thing I have to check it with is my eyes
Brightest bulb I've ever seen.Very white and
renders objecys in the sane color as sunlight..
I'm using some on my FW planted tanks and so far have been delighted with results.
May try one on a marine sump to seewhat happens
Gary fla.

 

[kris walker]

Thanks everyone for the replies. Unfortunately, I am still a little confused, but I stress it is just a little. I have 4 books on corals. Yea, I agree that Natural Reef Aquariums (one of the books I have) has a nice writeup...thanks Adrian. Three of the other books I have talk about the deg K rating. Two of the books are from Jim Fatherree (e.g. Soft Corals, Selecting and Maintaining..., TFH Books) and another is from Robert J. Goldstein ("Marine Reef Aquarium Handbook"). In both, they say actinic is 7100 deg K. So taking this at face value, and assuming it is true, the bluest *looking* light seems to be at 7100 deg K, not 20,000 deg K. In Fatherree's two books, he even continues to say that MH 10,000 K lights are "even bluer" than actinic. But they aren't really bluer *looking*, are they? I thought actinic was the bluest looking light one could get.
I read from people that 10,000-20,000 K MH light is bluish white. Since "white" light is really an amalgamation of different colors, I am wondering if the reason 7100 K actinic light is bluer looking than 10,000-20,000 K light is because the 10,000-20,000 K light has a *broader* spectrum, but still mostly in the blue end of the spectrum. Does this sound reasonable, or are these authors just plain wrong about the deg K rating for actinic lighting?
Thanks again, and great discussion,
sam
ps, Garfa, how can a bulb put out more energy than it uses? I don't see how that is possible. I think you have been biten by the "equivalency" confusion, i.e. the 65 input Watt "fluorex" bulbs brightness is as bright as that of a 500 input Watt incandescent bulb.

 

[predator]

Huh???

 

[q]

He is wrong or you are miss reading something.

 

[garyfla]

HI
Fluorex bulbs These are a screw in type mogul base,cluster fluorescent.According to the box they are the "equivelent to a 500
watt incadescent.120voltAc 60Hz compact
fluorescent
From box:8255 lumens brightness lumens and resulting claims are based on studies at
Lawrence Berkeley labs on phototopic luminance and perceived brightness Brightness lumens are not equivalent to photopic lumens
as referenced in ANSIphotometric tests and should not be confused
Now you know as much as I do lol.I've only had 1 for 3 weeks and added another last week.On aplanted FW 75 with 20 species of plants.So far I'm impressed.
Garyfla.

 

[kris walker]

Thanks for the info garfla. I will have to check them out if I run into them at my lfs.
As for my previous post, I am not misreading. Q, if those two authors are wrong, can you tell me what deg K rating actinic light should be roughly?
sam

 

[garyfla]

Hi Sam
You won't run into the fluorex lights in your lfs. The only application I've seen so far is for "task lighting" bright lighting for work areas.They are nopt made for aquarium lighting.I was just impressed with how bright and white they are Since I needed new bulbs I thought I'd try them out.Only cost 25 dollars fixture and all.
The only part of the Kelvin index I'm even vaguely familiar with is for rating stars.I think that's what the system was invented for and it helps classify magnitude,
distance and intensity of glowing objects
such as stars As related to artificial light
it seems to be a color rating index Red being the weakest and blue the most intense.
I don't know if you do any diving but it
doesn't take a scientist to see that the red through green spectrum give out real fast in
ocean water.But there is still visible light
at 110 feet(deepest I"ve been)everything appears blue.You notice this in photographs
As it applies to coral,blue is the only color available below about 20 feet so they
must be using actinic radiation for
photosynthesis? What I've read and observed
convinces me that color is far more important than intensity.My.02 cents.
Gary fla.

 

[kris walker]

Thanks Gary. Do you think they are at Home Depot? I'm interested in taking a detailed look at them, and if they will work form my setup. But I probably will stay with VHO bulbs just because that was part of my 6-month plan.
sam

 

[q]

As Adrian said actinic bulbs are rated differently. I have only seen 20K MH pics but I would say that the actinic have more blue that or just less intensity so it would be hard to tell.
Coralife makes a 20K VHO but I havn't seen it to compare it to actinic. I am not aware of how they measured it but as the eye goes the 6500K bulbs are not blue and the actinic is. If you want a rough guess then 20000K + give or take as the eye goes and in common talk among other reefers.

 

[adrian]

I think they are rated in nanometers, 420nm

 

[josh]

Yes adrian there are in nanometers, 420 being the most absorbed length, I also believe that 720 ( or 620 I forget ) is also absorbed very well, that is why acitinics have a 420 nm rating, no coeincednece

 

[kris walker]

Thanks Q, Adrian, and Josh. I know Adrian mentioned that before, but it just didn't seem to make sense to me. I mean, why rate actinic differently than the rest? It seems silly. No problem though. I agree that it should be 20,000+ K instead of 7100 K, I just wanted someone else to say that.
Best wishes,
sam