Originally Posted by megaredize
I have the 2.5 glass tank and i was thinking of making it a NPT. I was looking at LED lamps from walmart and some are pretty cheap. I think this would be a good idea for a light since the tank is small and obviously doesnt come with a light. How do i know how many LEDs i would need for a NPT of this size. im sure it wouldnt need to be too bright because of the size of tank. I will have anubias in the tank but i also want to put in other plants. probably medium light requiring plants.
For LEDs do figure out brightness by how many actual LEDs lights are in the lamp?? I dont know much about lighting especially when it comes to LEDs.
I spent quite a while trying to figure out how to rate LED lighting and thought I'd pass on this information.
Although LED's are rated in wattage in the same fashion as "normal" lighting, that value is of inconsequential use when attempting to determine the value of a light for a planted tank. The same can be said of the lumen values. Instead, the value commonly referred to for this function is "PAR" (or, photosynthetically active radiation). In simple terms, PAR refers to the amount of light that can actually be used at a given depth. PAR can be measured for readily using a PAR meter, but these meters are rather expensive and most aquarists will be unlikely to have one available. As a result, reference to the manufacturer's published data is your most likely source of this information. Note, however, that not all (or even most) manufacturer's provide this information.
There is currently a vast amount of information related to PAR values and determining the level of light, including various charts and measurements, available around the web. For my purposes, I agree with the information I've found elsewhere which refers to a PAR value between 10-30 as "low light," 30-80 as "medium light," and 80-120 as "high" light."
It should be noted that these values are at a given depth. As such, a light that has a PAR value of 120 at 12" will not achieve that at 18" or 24". Light diffuses rapidly at depth and the PAR value may be reduced by as much as 50% or more even by only adding 12" of depth. As such, you must determine the PAR for the depth you'll be working at for the reference to be truly useful.
There are two principal problems I've noted with LED's. One, they tend not to penetrate enough for good growth at lower levels. As a result, you'll have plants that are doing fine near the surface, but that may wither or die at lower levels (this is particularly true for plants that are not primarily oot feeders). Two, they tend not to diffuse well and so you end up having some very bright spots in your tank, but also very dark spots. Plants in the shadows will not grow as well, and so you must arrange them to make use of the light pattern.
As to the LED's you might find that are stocked at your local Big Box store or LFS, they may be fine for a small tank that is fairly shallow, but I suspect they will end up being insufficient in most cases. These inexpensive LED's tend to use low wattage (I.E., .06) bulbs that are highly focused. As such, their PAR value is substantially low and they are very much like spotlights. In addition, the color temperature may be very high (and is likely not indicated by the manufacturer) and less than ideal for plant usage. They may be great for appearance, but are of less use for growing plants. In contrast, they are inexpensive enough that it might be worthwhile to experiment with your setup.