If I did the math correctly, this is what you get from the 3 ansi designations for lights.

 

	beam spread (degrees)	tan(beam spread)	beam width at 100' (feet)	beam width at 200' (feet)	beam width at 300' (feet)	beam width at 500' (feet)
ideal taxi?	30	0.577	58	115	173	289
ideal landing?	10	0.176	18	35	53	88
eyf	12	0.213	21	43	64	106
eyj	25	0.466	47	93	140	233
eyc	40	0.839	84	168	252	420

 

 

Colyn,

 

Since the beam forms an isosceles triangle your formula in column C should be 2*tan(radians(angle/2)).   The widths are somewhat different for wider angle beams. 

 

I use a 12V 100W Halogen MR16 EMC (can't find the angle info) on the left leg for landing/taxiing and a GE quartz 12V 100W (Q4509?, 7 - 10 degree spread) cowling mounted lamp for approach/taxiing.  The GE provides good lighting of the runway on approach but disappears from view on flare (can't see over the nose) and the leg light beautifully illuminates the area I can see down and to the left.  I had pictures taken at night, but I can't find them at this time.