Rule of thumb, 219b is 30% more efficient than 219a (and 219c is 30% more than 219b)
example, 219b (middle) is 36% brighter than 219a (left):
Left: Niteye Eye10 TiC Titanium rotary w triple
N219a 4500k 9050 makes
306 lumens
Middle: Jetbeam TCR-1 Titanium rotary, converted to
N219b 4500k 9080 makes
415 lumens
Right: Niteye Eye10 with the stock 6000k XM-L makes
635 lumens
(the N219b is 35% less bright than the XM-L)
photo illustrates beam color, these lights are not on at Maximum brightness:
Next photo illustrates beam color of 219b 3500k 9080. It makes 350 lumens. (16% less than 219b 4500k 9080):
All the N219 LEDs are modifications, not stock.