Lighting values! Lux? Lumens? PAR? LED vs Fluorescent?


Lumens and Lux! PAR vs Watts per Gallon?!? Kelvins and spectrums? What the heck does it all mean?

I've been rolling along with a NO T5 dual light setup for my 26 gallon, socketed with two 14W 6700K daylight fluorescent bulbs. I hate that fixture. I want a new one.

I know watts per gallon is a good rule of thumb for fluorescent bulbs.
I know PAR/Lux is an important measurement, particularly when WPG breaks down because LEDs are involved.
I know lumens are in there somewhere, but more for humans and plants care more about PAR.
I know the spectrum is essential for plant life.

What I do not know, however, is how to convert each of these into an apples to apples comparison, so I know, when I buy my new fixture, that I am providing enough light for my plants. I don't need a detailed explanation of each term, that can be googled pretty well. I do need (or do I?) to know how to figure out how many lumens or the PAR/Lux values for my current setup, which one I need to focus on when I'm looking at other fixtures (HO fluorescent, LED, or even special Marineland Aquatic Plant LEDs), and what amount of lumens or PAR/Lux or WPG(LED-WPG) I should look at (assuming all lights are the same proper plant-growing spectrum, for simplicity)

Is this the best way to go about this? Or am I just way off?

Current setup (numbers from varied googling of bulbs)-
2 14W T5 bulbs = 28/26 = 1.1 WPG
1200 lumens per = 2400 lumens
PAR/Lux = ???????

New Setup (LED - Plant-special example)
23 white LEDs @ 1W each
4 RGB LEDs @3W each
PAR/LUX at 12" = 172/10530
PAR/LUX at 24" = 83/4810
Lumens = 2240

How do I know what fixture I need/want, giving plants enough light without too much light, and without blinding my fish?


I'm not sure about all the terms lol. here is a good link that will hopefully help you. I have no idea about led's I have never used them with live plants.

here are the links first is to help explain second is a cheap place to buy lights.


IV been trying to figure this out also. Right now I know that lux is lumens/square Meter. I see a lot of sites showing lux, so I'm thinking lux is a better way to judge the leds. Depending on how deep your tank is will show if you need to know par. I have a 40 gallon breeder planted, I took two 10000k led strips. Both 36" each and put them on top of my glass cover. They had more growth than my 36" dual t5HO 10000k bulbs. The LEDs are about 900lumens per foot. But since my breeders only 18" tall.. I didn't think par would really play too much of a factor in that tank. For me LEDs are up in the air haha. There are a lot of leds on ebay and around. Just find one iwith your need amount of lux. this really helped my decision on how much lux I need. give you a low down on lux and how much is needed to grow low light plants, medium light plants, and high light plants!

Hope this helped.


Hoppy's lighting chart is a great start for determining lighting intensity etc (doesn't cover LEDs):


PAR=a measurement of the spectral range of solar radiation in nanometers. 400-700 is required for photosynthesis to occur.

Lux=lumen per square meter. 10,000–25,000 lux = Full daylight (not direct sun). Basically what comes in through the window.

Lumen per watt of current lighting technologies:

Following is an approximate range of lumen per watt for popular light bulb technologies. See lumen.

Type of Bulb Lm/W
Incandescent 5-18
Halogen 20-25
(CFL) lighting 45-75
Fluorescent 45-125 (t12-t5HO)
LED 10-150

Read more:

I know from some indoor plant growing that I have done that a plant needs 50 watts per square foot. So if you have a two foot area you need light to grow the plant, you would need 100 watts.

The problem with aquarium lighting it that I don't know how the water effects how deep the watt of light will travel. When I search, I get underwater lighting for sale and no scientific information.


Welcome to Fishlore!

Because of the nature of LED, they really can't be compared apples to apples though they are getting close.

If you aren't looking to purchase a pre-built, there really isn't a set number/type of LED to use but you can use what other people have done or doing and copy or modify to your liking.

Most plants use the red spectrum (~660-700nm) and blue spectrum (~430nm). The RGB led wouldn't be worth it imo unless you are going for a certain look in the tank to need the green or you are very limited on space and wanting the RB on the same led. The Red and blue, unless you are going for grow light only may be overpowering in their colors. You want to make sure they are putting out the right spectrum as well.

Personally I am going with Royal Blue, Warm White, Neutral White and Cool White in my build.
8x 3w Royal Blue 440-450nm
4x 3w Cool White 6,500K
2x 3w Neutral White 5,000K
2x 3w Warm White 4,000K

The different whites give more redish as the K rating goes down while still giving off a "white" light. The blue is there to give the other spectrum the plants will use but is also there because the tank i'm using is a SW/FW and I want to keep the option to go salty later on.

Also, I'm using dimmers to control the light output, this can control your "wpg" so to speak as you can lower and raise the light needed for your plants.

Most prebuilt fixtures use 1w led's with optics to penetrate the water. In DIY, you can get 3w and 5w which will not typically require the optics(extra cost) and be able to use fewer leds further reducing cost. An example of a prebuil with 1w LED-

What LED's are you looking to use?
What size tank is this on, how deep is it?

Personally I would go with fewer higher wattage leds.


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