LED lighting for reef tanks is on its way to becoming a reality. Different LED fixtures address the lighting problem in several different ways, small number of high power LEDs with optics or with large numbers of low power LEDs with no optics.

The last article reported test results on some LED fixtures [http://www.advancedaquarist.com/2010/2/aafeature2] and their comparison to other lighting technologies. This article continues in the same vein and presents results on lighting output for some more LED fixtures available in the market. Table 1 presents a list of the LED lighting fixtures reviewed in this article. Each of these was tested using the same set up as my previous reflector tests, using a 3'X3' grid with a spacing of 3" in the X,Y direction. The fixtures were centered on this grid, and PAR was measured as PPFD (Photosynthetic Photon Flux Density) in micromoles/m²/sec using a LICOR 1000 data logger and a LI-192SA underwater cosine corrected sensor calibrated for both air and water. The data logger was set to average 5 readings for each data collection point. The data was imported into Microsoft Excel for analysis and the data was plotted to display the light spread and intensity at various distances. 4 plots of the data with 2 plots at each distance were generated showing:

• A 3-D surface plot showing the actual PAR values recorded
• A contour plot viewing the surface from the top showing the distribution

The LED fixtures tested fall into 2 separate categories - ones using fewer high power LEDs (Aquaillumination) and ones using large numbers of low powered LEDs (Eco-Lamps KR-91, Blue Moon Aquatics and Panorama). The low powered LEDs were tested at 18" and 24", while the high power ones were tested at 24" and 30".

While PAR values are are not the only things that we should be concerned about when purchasing an LED fixture, they are certainly the first criteria that must be met when selecting any lighting system. Additionally, more specifically with LED systems there are a host of other criteria that must be considered. While these criteria are more subjective and easily swayed by user preferences and values, this article focuses primarily on the light output and distribution.