# A discussion on Kelvin in fluorescent bulbs...



## breeze905 (Feb 1, 2009)

Ok... this is a topic of interest to me as I search and read so much yet I don't find clear cut answers.

I understand that the spectrum of light in the red and blue regions are important to the photosynthetic processes of plants and algae... and a lil of the green spectrum too.

I could be wrong on what i'm about to state but the measure of kelvin is a degree of temperature thus showing different hue's/colors on a black body. The source of light being the radiator. From what i understand an incandescent light bulb is a black body radiator in itself whereas a fluorescent bulb is not. (Please don't make me search for the reference of where i got this from... i been doing too much reading... could be hard.) Thus rating fluorescent lighting in kelvin is accually false...

either way... having peak spectrum emmissions in the blue and red regions are typically what benefit plants the most. the spectrum scale on fluorescents are actually just rounded off and nicely presented depictions of what the bulb is actually doing. The bulb actually peaks in certain points yes but may have minimal to no emmission of the colors in between the particular peaks. Thus creating a false kelvin rating.

Anyway.... (Damn encyclopedic posts!)

I have been looking at different lamps... was very disappointed to see that the life glo 2 is not made in 36" t8 size. I'm starting to think that maybe the algae in my tank is from the source of light. (haven't counted out silicates but maybe the spectrum of light is effecting the tank in more ways than i had accounted for.) I think that if i had a better light spectrum for my plants that the photosynthetic process would be stronger and use more nutrients from out of the water so the algae would have less to thrive on.

Currently i run two 36" 30 watt t8 phillips cool whites. Now i've read reports of plants growing under these lights with ease but definitly grew better with lights designed for growing plants.

Now that i am willing to change out the lamps to see if it will make a difference... i'm very curious as to which direction i should head with the next bulbs. I went to big als hamilton for lamps and didn't find any that i wanted to try in the right size. Currently i'm thinking about going with the zoo med flora sun max plant growth lamps which say the have peak spectrum emmissions in the blue and red for plant growth. 8500 K. i'm gonna put one of those in with probably the closest thing to 6700 K I can find whether it be a phillips daylight or the zoo med ultra sun.

I posted this to see what other people thought about kelvin and their understanding of it and it's relation to plants and algae.


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## Darkblade48 (Jan 28, 2008)

I'd just like to point out that a lot of the fluorescent tubes that are branded for "aquarium use" often have strange Kelvin ratings. For example, the Zoo Med Flora Sun Max Plant Growth bulb claims to have a rating of 8500K. I kind of doubt this, mainly because of how manufacturers to have skewed ratings. 

Another example: Hagen has bulbs that claim to have ratings of over 10000K that are still suitable for a planted tank. And yet, we know that anything over 10000K isn't really suitable for plants (because you'd be pushing beyond the blue part of the spectrum). 

Please, please don't make me pull out the physics calculations to show this. 

As for the statement that a fluorescent tube is not a black body radiator, this is correct. Fluorescent bulbs (naturally) work differently from an incandescent bulb. By using electricity to excite the electrons of the (various) gases inside the fluorescent tube, they will jump up to discrete orbitals. They will also subsequently fall back down into their ground state, releasing the energy that was absorbed. This energy is then emitted and absorbed by various phosphors that coat the inside of the fluorescent tube and can be seen as light.

Hope that wasn't too confusing, I tried to explain it with as little physics as possible.


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## Zebrapl3co (Mar 29, 2006)

I think you are complicating thing by trying to understand how the light is design. Unless you are so good that you want to branch out and design your own perfect flourescent light source. I'd recommend you stick with what has worked for everyone.
Lets start with the wattage, understand that wattage is the first thing that you should be thinking about. So you have 60 watts on a 30G. That's not bad to start with, but understand that your set up is not a high light set up.
Life glo 2, I think is a Hight Output (HO) light. That means, you need a high output lamp to use it. I believe the wattage out put for a HO is more wattage.
Your second concern is correct. K (temperature) rating is important. All "cool white" light sucks. And yes, I tend to agreed that they promote algae growth, but if you manage to balance it well, I've heard that you can get away with it. I have no such luck with cool white light. You should be looking at "daylight" light. They have a higher K rating. I think it's around 6400K. That is closer to sun light, hence the plant will benefit from it. If you have any red plants, then you will need a higher spectrum light. Otherwise, your plant won't turn as red.

Edit: Holycow, we have a physicist in the house!
LOL, I understand exactly what you're talking about, but I just can't explain it way you did. And yup, I agree with you. I think those 10000K rating are simple marketing bullshit.

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## Calmer (Mar 9, 2008)

You may want to try some faster growing plants to compete with the algae for nutrients. Faster growing plants like floating or stem plants. Java Fern and Anubias Minima are slow growing plants.


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## cablemike (Jan 7, 2009)

upgrade yoour lighting to hagen t5 and they make lifeglo in 36inch for the t5 units. hagen is moving away from t8 lighting in favor of the much better t5.


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## Darkblade48 (Jan 28, 2008)

Zebrapl3co said:


> Edit: Holycow, we have a physicist in the house!
> LOL, I understand exactly what you're talking about, but I just can't explain it way you did. And yup, I agree with you. I think those 10000K rating are simple marketing bullshit.


Off topic: I'm not a physicist, I have a degree in microbiology  I just take the other sciences as a hobby (especially chemistry).


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## moon (Mar 11, 2006)

In order to get the best of fluorescent lighting you should be looking at CRI (colour rendering index) and CT (colour temperature). CRI at it's highest of 100 offers the best colour rendering. Colour temprature is the appearance of the lamp with respect to it's spectral composition and does not necessarily have good colour rendition.
A black body radiator is an incandescent source with a CRI of 100. As the temprature of this source is increased the spectral appearance of the body changes. The CT of fluorescent lamps are compared to the absolute temprature black body radiator. At a CT of 3000K the colour is warm in appearance at the other end of 8000K the appearance is very cool. Sunlight has a CT of 5000K whereas a cloudy sky is at 6000K. A clear sky without sun is 7000K. 
Hope this makes sense.


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## ameekplec. (May 1, 2008)

It's also not limited to the wattage of a bulb or the apparent colour temperature, or the output (Lumens), but the PAR (Photosynthetically Active Radiation) of the bulb and what's reaching your plants.

PAR would be your best indicator of the suitability of a bulb for your needs, as all the other 'indicators' (ie wpg, K rating, etc) only give you a rough idea of what you're putting over your tank. But I know a PAR meter is not exactly something people have lying around (I do ).

For the algea, try lowering your nutrients in the water, as well as cutting back your photoperiod. Cutting back the photoperiod is IMO one of the easiest, more effective ways of getting rid of nuiscance algaes.

As for the tech discussion, I know T5HO/NO are the way of the future, but there are some good T8 tubes being developed too. But I'd stick with T5s for any freshwater application as the availability of 6700K bulbs (which are most aesthetically pleasing with the lush greens and reds of a planted tank) is not the same like you have noted with T8s.


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## breeze905 (Feb 1, 2009)

Zebra... i wasn't aiming for a high light system... i was more looking for a low light no co2 type of setup...

Calmer... I would love to plant faster growing plants but currently i don't know of any that can grow in low to moderate light settings. So... if you have any information i can use... hook me up!

moon... What exactly does the color rendering index mean tho... if the CRI is at let's say 98.1 does that mean that 98.1% of the different colors in the full spectrum are being emitted from that lamp? (I don't beleive that is the case.)

The photosphere of the sun supposedly has an effective temperature of 5778 K...

Anyway... I was interested in the flora sun by zoo med not really because of the 8500 K rating but the fact that it said it's peak emmissions were in the blue and red regions of the color spectrum. I figure i mix that bulb with a 6400K - 6700K daylight bulb to get more of the in between blue and red colors for the plants. the blue and red provided by the flora sun bulb. Theoretically i think this is a good combination of lights for plants spectrum wise.

I am a lil strapped for cash right now so dropping $80 on a dual t5 strip light when i have dual t8's running right now just doesn't seem very economical... (I know spending helps our economy... but not if i go broke!)

But yeah... I definitly like the discussion we're having... Spectrum might not be the end-all be-all but i'm pretty sure its a topic that's been on everyones mind at some point in our fish hobby careers.


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## Calmer (Mar 9, 2008)

breeze905 said:


> Calmer... I would love to plant faster growing plants but currently i don't know of any that can grow in low to moderate light settings. So... if you have any information i can use... hook me up!


Some fast growing stem plants are:
Hygrophila corymbosa
Hygrophila polysperma
Limnophila sessiliflora
Rotala rotundifolia

You can have a look here for more fast growing plants: http://www.tropica.com/default.asp If you are using the two 36" 30 watt t8 phillips cool whites on the 33 gal.aquarium then your lighting is probably considered medium. 
If you get out to the east end sometime then let me know as I can set you up with some free fast growing plants to get you started. Also check out what ameekplec. said above about getting rid of algae.

You may also like to read this post as well:
http://www.barrreport.com/general-plant-topics/5420-plants-do-use-green-light-mostly-some-cases.html


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## Zebrapl3co (Mar 29, 2006)

Hmm, I always though that CRI is an indicator of how close you are to natural sun light. The further you are away from the 100%, indicates the how unrealistic the source of ligth is casting.
As ameekplec has said, and I agree. PAR is the perfect measurement of how much light your plant is getting. I think if I remember correctly, it's also a method that NASA is using for measuring they plant experiments as well.

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## Chris S (Dec 19, 2007)

Well, I'll tell you what has worked wonderfully for my low-light plants.

I have 2 20g tanks with anubias, moss, java fern, various crypts and pygmy chain sword. 

Each of the 20g tanks is lit by a T-5 coralife 22" fixture using two 6700k 'Plant Lamp' bulbs (replaced the ones that come with it). Each bulb is 14W and I run them for around 8 hours a day (on and off throughout the day).

Little to no algae problems, good plant growth. Recently I've introduced co2 to both systems, along with a small amount of fertilizer which has moved the plant growth from good to excellent without any algae problems.

The same type comes in 24 (actually 22, with extensions), 30, 36 and 48 inch fixtures.

I've had 0 problems with either and highly recommend them.

I'm sure some others also use them. You should be able to get them at Big Al's, but Harold at Menagerie might be able to give you a better price.


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## ameekplec. (May 1, 2008)

I use this fixture too, and it's great, and fairly cheap and looks decent too.


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## breeze905 (Feb 1, 2009)

well i did get some t8 6700K bulbs... life glo 2's. they were too expensive for my liking but i have no other options really at the 36" mark. Now if i needed 48", philips and ge make 4' daylight fluorescents, but 3' are a rarity. As for the change in Kelvin and noticing a difference. I do. Definitly getting better better development in the plants. Before they seemed like they were getting worse all the time. the algae would grow back on them in a matter of a few hours. now the leaves look stronger and look healthier. the algae growth has slowed a little... i went at it with a cleaning and a little water change and severely harmed the algae growth. i definitly beleive that the kelvin rating in these bulbs allow for better photosynthesis and so the plants use more of the nutrients giving algae less to feed on. Thanks for the input everyone and I'm a believer.


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