True actinic bulbs are 420nm, while marine blue bulbs are 460nm. Both promote Chlorophyll B photosynthesis but sorely lack the red end of the spectrum (ideal ~660 nm) required for optimum Chlorophyll A photosynthesis. A 50/50 bulb is okay to use but I wouldn't use it alone. It would be good paired with a 5000K bulb. Otherwise, I tend to avoid the use of actinics in freshwater planted tanks and stick with full spectrum daylight bulbs in the 5000-10000K range if using a single light source. Bulbs with a high CRI rating will give the truest color rendition, as well. While this isn't vital for plant photosynthesis, it will greatly improve the overall appearance of the tank and allow for a more natural look.
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