The higher the K number, the bluer the color of the light. Plants need both the red end for spike development and the blue end for vegetative growth. There are specific color temperature needs, but if you can only use one bulb, try for a "full spectrum" bulb that provides light at both ends of the spectrum as well as middle of the spectrum for esthetics (plants don't need very much in middle, but humans see better color rendition in middle range.)
Try this company to see if you can get a "full spectrum" replacement
2 to 200 Watt Compact Fluorescent Bulbs : 1000Bulbs.com The Light Bulb Superstore.
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Ross
http://orchids-ross.blogspot.com/
I don't do most Dendros or large, "floofy orchids". For me it's minis (like Angraecoides), Masdies, Paphs, and others that crept in somewhere along the line. See my orchid list for complete collection (usually not current.)