# what is the difference between 5000k and 6700k?



## abc (May 18, 2004)

Hello! 

I'm ordering the bulbs for the retro-fit 55w lights. I'm thinking of going for the 5000k 55w bulbs because it's not as bright as the 6700k and from the ahsupply website: it does NOT make a difference in plant growth. If that's the case, then would it make a difference in HEAT? if the 5000k bulbs generate less heat, then I definitely want to opt for them. But if it does not make a difference in HEAT either, then it's just a matter of looks/appearance? if I like bright lights (6700k) or dimmer ones (5000k)? What is "k" anyway? It can't be kelvin, can't it? kilowatts?

It sure is hard to get the technical linguo down since everyone is using it on the board with the assumption that people know what the abbreviations mean, but for a newbie, it's a killer trying to hunt down the references to the abbreviations. We ought to have a general post up in the FAQ index for abbreviations. Anyways, can someone help me out here? Thanks! abc


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## SCMurphy (Oct 21, 2003)

It is Kelvin temperature, which is a measure of the color of the light bulb output in relation to daylight. Think of 5000k as being a bright overcast day, and 6700 as a bright blue sky day. If you see a 10,000k bulb think of the brightest, most blinding blue sky, you've ever seen. 

There is no difference in the heat output from the different lamps based on K. You will see less heat from a lower wattage light but not from a lower K or CRI (color rendering index, 100 is perfect).


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## BigBlue00 (May 11, 2004)

Hi,

I am a fellow newbie myself, but have read and learned alot from reading this board and other Internet sites.

It's really the best way to build your knowledge about all the things that you need to know about in having a planted (or any) tank.

Anyways, from info on the net and my experience, plants do best under 5000K - 6700K full spectrum lighting. The lower K numbers usually have a yellower tint to them, and the higher ones are more bluish. So it boils down to personal viewing preference. Your plants will like it just the same (with all other things being equal).

I recently changed my 8800K PC (Power Compact or Compact Fluorescent) bulbs in my CustomSeaLife (CSL) BriteLite strip to 6500K bulbs, and the tank looks more yellowish.


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## abc (May 18, 2004)

Well, I read this post too late. I tried to change an online order for 5000k lights, but the shipment was already sent. Darn! Darn! Darn! If I had known a couple hours earlier, I would have gone for the 6700k lights. Oh well, my tank will have a nice sleepy look it. Thanks for the info! abc


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## malkore (Nov 3, 2003)

You probably won't see a difference between these bulbs, unless you have 1 of each, running side by side. THen you'll see that the 5000k is a little more yellow than the 6700k.
Your plants and fish won't care either way, so don't get bent outta shape.
Consider it an experiment


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## louisxyz (Apr 8, 2004)

BigBlue00 said:


> Hi,
> Anyways, from info on the net and my experience, plants do best under 5000K - 6700K full spectrum lighting. The lower K numbers usually have a yellower tint to them, and the higher ones are more bluish. So it boils down to personal viewing preference. Your plants will like it just the same (with all other things being equal).


The K refer to the temp, but we have to consider the color spectrum, so over 5000K we get usually more blue and less than 5000K more red. The plant need to get color from the all color and it why "full spectrum" bulb are prefer. So if you have enough room, you should get 6500K and and 3000K then you get both blue and red sectrum. If you use Triphosphor bulb like Hagen PowerGlo, then you get color from all spectrum, but if you use normal bulb, than again you should try to use both, the color rendering will be better with both 6500 and 3000k bulb anyway.

On my 6 T8 fluorescent setup, I'm using 2 phillips TL950 (6500K with 98 CRI), two TL930 (3000K) (CRI 95) and two powerglo de Hagen.


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## 2la (Aug 18, 2002)

BigBlue00 said:


> Anyways, from info on the net and my experience, plants do best under 5000K - 6700K full spectrum lighting.


You must not have read any of _my_ messages, then.  This notion of plants doing "best" under such lighting is the company line but I and many other people who heavily employ bulbs rated at 9325K would beg to differ. The bottom line, though, is what you actually concluded from this statement, and that's that color temperature is purely a matter of preference to _your_ eyes, not the plants'.


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## BigBlue00 (May 11, 2004)

2la said:


> You must not have read any of _my_ messages, then.


Hehe, like I said I am a newbie on this board so I haven't gotten around to a lot of the forums here yet. 8) 



2la said:


> This notion of plants doing "best" under such lighting is the company line but I and many other people who heavily employ bulbs rated at 9325K would beg to differ.


It seems like the general consensus is that the PAR/PUR a bulb gives off is the "best" measure of the quality of a plant bulb. A bulb can have whatever temperature as long as it has good quality red and blue that the plants can use.


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## malkore (Nov 3, 2003)

The K ratings used to be our best way to determine if a bulb was good. Nowadays, however, the bulb companies use more than 1 phosphor coating inside the tube, so the K might be the same, but the CRI is better.


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