Question
i was planning on making a ~10 gallon hexagon viv. for masdvallia, specifically howeara lava burst orchid.

*what wattage light should i use?
*if the tank is about 10 inchs in diameter what would be the best kind of light to use?
*for one orchid could i use a light that puts out 910 footcandles?

Answer
Rich, you will need to check the light level at the level of the plant leaf.  If you are referring to the light output (ie 910FC) at the leaf level, that probably is fine for the Masdevallia, but you will need a bit more for the Howeara.  You need at least 500 FC at the leaf level for the Masdevallia.  If your light fixture is at least 12-18 inches above the plant, you will need at least 80 watts of lighting for 500FC at the plant level.  Also, find a way to avoid overheating so a florescent system would be good.  A humidity of at least 80 percent is desirable.  Plant some live moss along with the orchid.  If the moss thrives, the orchid should also.  Doing this with a single plant is a wise idea until you get the conditions right.   The conditions will need to be adjusted as you go along.