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Ok, I know there have been like a million posts about "what light should i get", but i haven't really been able to extract the information that i am looking for from any of the other posts.( i have been looking for quite a while haha). I currently have a 48inch fixture that has two 65watt PC bulbs. I paid a little over 100$ for it about 2 years ago ( yes it still has the same bulbs) Now i have defiantly noticed a lack of growth for quite a while now (due to the old bulbs im assuming), but i just cant imagine spending 25-30$ per bulb to replace them. I also noticed that my PC's get a little hot and i think that they are burning my plants when they grow high enough in the tank.

Keep in mind i am a very big DIY person so My question is, would my plants do better if i bought two T8 fixtures from home depot total 36$. Each fixture will house 2 bulbs, for a total of 128 watts, and mount it up inside my hood.

Another question and i think this is more the main question is about the bulbs, they have a few different types at home depot, a pack of two of 4100k, 2850 lumens, is 5.97. there are also some that are 5000k, 2950 lumens, but these are 7.46 each

I have read on many forums saying that the K rating should be at least 5000K ?? is this correct? i have also seen people saying that the K rating doesn't make a difference?? is this true.

Thank you for any input.
chris
 

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I'm not qualified to recommend a course of action. I am somewhat qualified to comment on the bulbs. The K rating on bulbs is BS, but that's not to say that the spectrum of the output is not important.

Black bodies have a spectrum that looks like this graph, and it shifts depending on temperature. It moves to the left in this graph:


Fluorescent tubes have spectrums that look like this:


I think that what that all boils down to is that you want to buy a bulb that someone else has said is ok for growing plants (or experiment yourself), and choose a K rating, which is going to indicate an approximation of the color, that is to your liking. High K ratings = bluer bulbs, lower = redder.
 

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i believe the 5000k bulbs would work, but would maybe be a little orange or red in appearance and won't be very aesthetically pleasing, such as a normal screw in incandescent light bulbs.
 

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The peaks on chlorophyll a and b are the wavelength outputs of light that you are looking for. Any light that peaks at those should do well. The 2 watt per gallon rule is a good one to follow. I keep reading that color temperature (K) doesn't really matter. I don't know about all that.


The whole kelvin thing and light temperature stuff came from the study of thermal radiation of blackbodies. Charcoal is a good example of a blackbody, or think of hot lava...its red! That's due to the fact that it's superheated--I'm guessing around 2500-3000k. Planck (i think) heated carbon and studied the color it emitted at different temperatures. That's where the scale came from. Stars twinkle red and blue because they burn at differing temperatures.



Light, radio, and microwaves are all types of electromagnetic radiation. Radiowaves are super-low frequency, huge wavelength waves. Red is a low frequency (frequency = the number of wavelengths that pass a point in a second.) and larger wavelength light. Blue is high frequency and short wavelength...compared to red.

Anyway.... As temperaure increases, the amount of radiation emitted increases, across the spectrum. High K lights appear bluer because they peak at shorter wavelengths. Example = bluish HID high K headlights. SO, K matters, and high K lights peak in the blue region + they emit more radiation across the spectrum....so you get more red light as well. The higher the K temperature the better, because your light peaks at blue, but still has high radiation throughout the spectrum---Chlorophylls a and b get a huge dose of blue, and a good dose of red. ALSO, your fish will fluoresce beautifully in the high K light, and your plants will look super green.

I used a 12000 K 65watt compact fluoresecent on a 30 gallon, and it worked great.
 

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PAR meter fans disagree strongly with this chart.


These are some pretty knowledgable folks in the hobby, and their chart looks like this:


I don't agree or disagree with anybody in regards to the spectral response of chlorophyl because I don't know anything about it.

To reiterate what I said before to the OP, if you choose to go this route, I would recommend you find a specific bulb that someone you trust has recommended, or you can experiment and let us know what you learn.
 

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PAR meter fans disagree strongly with this chart.

These are some pretty knowledgable folks in the hobby, and their chart looks like this:

This is a graph of the Apogee Quantum Sensor and the wavelengths of light it detects. It does not contain any information relevant to the posts. The graph shows how well a light meter detects visible light. Visible light is the same as PAR (photosynthetically active radiation), which is the same as quantum light, which is pretty much the same as solar light.

The graph is high in the 550 nm region. 550 nm is green light. Plants are green, because they reflect green light. If the light is being reflected, then it isn't being used for photosynthesis. This is a fact that proves the graph has nothing to do with the correct wavelength of light for a plant.

The graph does not provide a basis on which a PAR meter fan could disagree.
 

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don't change your PC for T8 fixtures. All lights will need new bulbs annually, some sooner. If you want to change fixtures, look at T5 HO. They are a bit more efficient, but I'd just get new bulbs.
 

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This is a graph of the Apogee Quantum Sensor and the wavelengths of light it detects. It does not contain any information relevant to the posts. The graph shows how well a light meter detects visible light. Visible light is the same as PAR (photosynthetically active radiation), which is the same as quantum light, which is pretty much the same as solar light.

The graph is high in the 550 nm region. 550 nm is green light. Plants are green, because they reflect green light. If the light is being reflected, then it isn't being used for photosynthesis. This is a fact that proves the graph has nothing to do with the correct wavelength of light for a plant.

The graph does not provide a basis on which a PAR meter fan could disagree.
Then what good is the PAR meter again? I thought it measured light available for photosynthesis. You're saying it's just a random band gap?
 

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Unfortunately, the inexpensive bulbs at Home Depot and Lowes usually don't have charts indicating the spectrum. So, you might be dealing with mixing and matching bulbs looking to match the ideal spectrum. A lot of trial and error. There are very good T8 bulbs for growing plants, you can get them from the usual online aquarium stores. Then you are back to spending $15.00 per bulb x 4. You might be better to replace your PC bulbs or better yet, go to a new T5 HO fixture.
 

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Then what good is the PAR meter again? I thought it measured light available for photosynthesis. You're saying it's just a random band gap?
I posted all I know about PAR meters. I had never heard of them until you mentioned it, but I did some research. Otherwise, I'm just saying that the Apogee graph doesn't disprove (nor could it disagree with) the one for the activity of chlorophyll, because it isn't related to it. From what I've read, PAR meters do measure light available for photosynthesis. All light is available for photosynthesis, but red and blue wavelengths are the most readily taken up by chlorophyll.
 

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Just purchase new PC bulbs. As one of the ultimate DIY light guys, I've got to say that simply fixing what you have is easier and ultimately cheaper. After you change the bulbs, start watching for a deal on a T5 HO fixture.

To save money on your bulbs, check out your local electrical supply shop. They can order most anything you'd like. Otherwise, order on line.
 

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I posted all I know about PAR meters. I had never heard of them until you mentioned it, but I did some research. Otherwise, I'm just saying that the Apogee graph doesn't disprove (nor could it disagree with) the one for the activity of chlorophyll, because it isn't related to it. From what I've read, PAR meters do measure light available for photosynthesis. All light is available for photosynthesis, but red and blue wavelengths are the most readily taken up by chlorophyll.
Tell Hoppy and Plantbrain what you've learned, and report back.
 

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Discussion Starter · #16 ·
thanks for all the advise, i think i will just keep my eye out for a t5 fixture, and take a look at bulbs for each setup again, ( price comparison)
 
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