# Daylight or coolwhite?



## s0mt1nf1shy

Which is better for plants & which looks better..Daylight or coolwhite?


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## neonfish3

Definitely daylight spectrum is better to look at. 
I'm positive both will grow plants just fine.


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## John N.

Daylight seems brighter and looks better. I would go with daylight. I never tried using cool white, since daylight grows my plants just fine.

-John N.


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## AaronT

You will want bulbs that have a kelvin of somewhere between 5,000k and 10,000k. They tend to have the spectrum of light that plants need to grow. 

The coolwhite bulbs tend to be 3,000k and 4,000k bulbs and aren't really suitable for our purposes. If you are using T8s and are looking for something on the cheap go to your local hardware store and see if they carry Phillips daylight bulbs. They should be $8.00 or so for two of them.


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## AnthonyN

You may want to check out an experimental study that appears in Diana Walstad's book "Ecology of the Planted Aquarium". In this study 5 freshwater plants where grown under different types of lighting to see the effect on oxygen production. The highest oxygen amounts where produced with a combination of a full spectrum bulb and a cool white bulb. This study seems to suggest that a combination of bulbs that includes a cool white produces the highest levels of photosynthesis.

Anthony


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## ruki

*cool white better than daylight (Walstad's book)*

bump!

Page 180 had an experiment where cool white was better than daylight.

No one commented on this...

This was quite an unexpected result.



AnthonyN said:


> You may want to check out an experimental study that appears in Diana Walstad's book "Ecology of the Planted Aquarium". In this study 5 freshwater plants where grown under different types of lighting to see the effect on oxygen production. The highest oxygen amounts where produced with a combination of a full spectrum bulb and a cool white bulb. This study seems to suggest that a combination of bulbs that includes a cool white produces the highest levels of photosynthesis.
> 
> Anthony


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## Newt

John N. said:


> Daylight seems brighter and looks better. I would go with daylight. I never tried using cool white, since daylight grows my plants just fine.
> 
> -John N.


If it appears brighter to us (humans) then it has more green which does ziltch for plants. As you can see from the attched graphs the cool white has better light (red and blue) for plants. Appearence of what a particular light produces is totally subjective to the viewer.
GE Daylight:








GE cool white:








Philips C50 and C75:









Once again, kelvin rating has nothing to do with how well it will grow plants. It is how it will make your plants look to you.


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## VITARTE

Aren't daylight bulbs supposed to imitate best the way sunlight reaches us, say, at noon? 
I mean, that'll grow any plant, right? ( provided there's also enough water, nutrients, etc)
I've always used daylight bulbs in my tanks and I also have to say it grows plants just fine.
Just my 2 cents.
Rafo


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## Newt

Just about any lights out there will grow plants. BUT the best light for plants are the ones with large peaks in the blue (430 to 450 nm) and red spectrum (625 to 675 nm) and a spike in the green to add brightness for our human eyes.


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## panaque

I look for the "k" value on the bulb as well as the lumens (the amount of light). I use ecolux wide spectrum bulbs found at the hardware store for around $6 a piece. Having good results...


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## Newt

panaque said:


> I look for the "k" value on the bulb as well as the lumens (the amount of light).


A higher lumen rating at the same wattage often means greener light. Lumen is a rating weighted entirely to human perception. It has little to do with the value of a light for either growing or viewing plants.

Lux is lumens/square meter, so they are similar. They are both defined in terms that are meaningful to human perception of light - not plants. They stress the amount of energy in the green band to which humans are most sensitive - not plants.

Artificial light sources are usually evaluated based on their lumen output. Lumen is a measure of flux, or how much light energy a light source emits (per unit time). The lumen measure does not include all the energy the source emits, but just the energy with wavelengths capable of affecting the human eye. Thus the lumen measure is defined in such a way as to be weighted by the (bright-adapted) human eye spectral sensitivity.

The standard measure that quantifies the energy available for photosynthesis is "Photosynthetic Active Radiation" (aka "Photosynthetic Available Radiation") or PAR.


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## yxberia

I used to have 2 Cool White CF in my tank, I have removed them since red plant does not show interest in them.
I am using Warm White (normal Philips 3000K) coupled with Hagen Power Glo now. Both my red and green plants like it very much. I think most green plants will do fine with Daylight/Cool White.


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## SUBORPHAN

Newt said:


> If it appears brighter to us (humans) then it has more green which does ziltch for plants. As you can see from the attched graphs the cool white has better light (red and blue) for plants. Appearence of what a particular light produces is totally subjective to the viewer.


Amano is selling two types of HQI bulbs a normal one and one with added green. if green does nothing for the plants then is the added green purely to give more brightness to the tank?


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## Newt

Simple matter of photosynthesis: plants can only utilize light that is absorbed. Plants appear green because it is reflected light.

So, yes. The extra green would only be a benefit as added brightness to human eyes. Actually it is more difficult to make a bulb that utilizes Hg with less green.


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## snoopy

Can I ask for the CRI parameter in the bulb. As I know it is Color Rending Index and it compare the similarity of the bulb's light and the sunlight. 

And I have read the information: bulbs have CRI > 85 are suitable for planted tank. Is that information correct?


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