Lighting Confusion : A Little Help

K refers to the color temperature of the light. Which is expressed in degrees Kelvin. Which is different from the intensity of the light. Basically the lower the color temp the warmer IE yellower or redder the light is. And the higher the color temp is the bluer the light is. Generally for planted tanks you want to mimick the sun so you would want something in the 5000K to 6500K. Those 10,000K and 20,000 K bulbs are for reef tanks as the deeper water in nature filters out alot of the yellow and red parts of the spectrum. Hope this helps

i think anywhere from 5000-10,000k should be fine. only your preference would play a role within these ranges. some reports that 10,000k promotes more algae growth, but i have yet to notice that happening in my tanks. i tend to prefer the "raw" bluish light for certain tank setups, whereas a 5600k will give you a warmer, in-the-beach impression. it's really up to what you prefer.

The short answer? Light intensity is far more important than color spectrum.

The long answer? Excess output in the wrong spectrum (yellow/green) will allow the opportunistic algae to take advantage of it if plants aren't growing fast enough. This is mostly noticeable when light intensity is marginal (less than 2 wpg). If there is enough output in the red and blue spectrum, plants will grow so quickly that they will outcompete algae for nutrients easily.

Your best bet? Bulbs in the 5000K to 6700K region. Even better? Plant growth bulbs with specific red and blue output such as Sylvania's Gro-Lux or www.PetSupplyLiquidator.com 's plant growth Power Compact bulb.