Hey there, I am a new bee to this forum. I just went through the post put up and it rang a bell. I was like
. This is what I got to know reading various articles on lighting requirement for planted tank.
Plants require red and blue light of the visible spectrum for photosynthesis. They reflect most other lights. Red light is of shorter wavelenght and hence is lost. Blue light are of higher wavelength and penetrate deeper into the water. The watts per gallon is a myth. Now then what lighting would you want to choose for? There are range of lightings from CFLs to LEDs to the old T8, T12, MH, HPS etc. One common thing to all these is that they all have a kelvin rating. The temperature of light color is measured in kelvin. The CFL's color temperature is 6500K, which is close to the color of Sun's light on a very clear mid noon. A minimum of 6500K is good. The watt rating on bulb is a measure of the energy it consumes and higher watt means more bright light. But remember, a 45 watt spiral/tubular CFL wouldn't give any more than 6500K and similarly a 5W spiral/tubular wouldn't give any higher than 6500K. I checked all the CFLs in the market and they all have 6500K. From 5W to 45W. A higher Kelvin would be required in case the depth of the tank is more than 20 inches. My tank has slot for two bulbs, one at left and one at right. I put a 20W spiral CFL in one slot and boy the water heated up quickly(the other slot was empty). I have a 22*9*13 inch tank. Imagine if I had put another 20W. For instance, If i were to have two 20W or any watt rating CFLs for that matter (they all are of the same kelvin rating 6500K mind you), it wouldn't be 13000K. I returned the 20W CFL and am to put up two 5W tubular CFL. The difference between tubular and spiral is in the light intensity measured in lumens. During winters we would alway require a heater and defenitely not rely on the energy from the bulb. Am not sure if you guys are doing well with bulbs of 20W. Isn't that raising the water temperature? We may have to keep the water temperature at the optimum for the fishes we have as each's requirement is different.
You may have stumbled across the terms PAR and PUR. They are Photosynthetically Active/Used Radiation respectively. These only apply to lighting stats in aquarium. We would not be able to find this on any bulb. PAR is a measure of the spectral length of the visible light ranging from 400nm to 700nm, nm is nanometer. PUR is the useful light of that spectrum that plants require which is 440nm to 490nm. Blue light falls within this.
I welcome all/any correction on this. Thank you!