Does this formula apply to all incans, or only halogen?
It's kindof a general middle of the road for re-rating halogens... for rough estimates it works with most halogen and xenon bulbs reasonably well. Some manufactures will give their own re-rating formulas because different bulbs re-rate differently than this "standardized" formula. There are also more halogen formulas...
formula for halogen lumens re-rating:
Lr = (Va/Vd)^3.5*Ld, where Lr is re-rated lumens, and Ld is design lumens, and Vd is design voltage and Va is applied voltage.
formula for halogen lamp life re-rating:
Lr = (Vd/Va)^12*Ld, where Lr is re-rated life, and Ld is design life, and Vd is design voltage and Va is applied voltage.
formula for halogen current re-rating:
Ar = (Va/Vd)^0.55*Ad, where Ar is re-rated current, and Ad is design current, and Vd is design voltage and Va is applied voltage.
formula for halogen CCT re-rating:
CCTr = (Va/Vd)^0.317*CCTd, where CCTr is re-rated CCT, and CCTd is design CCT, and Vd is design voltage and Va is applied voltage.
This is what is throwing me off... are reflector surfaces really that inefficient that third of the light is being absorbed? Even if a glass lens isn't anti-reflective coated, most of the light that makes it through the first time should bounce back into the reflector, then back out of the light the second time (as spill). 65% losses would seem to suggest that reflector surfaces are only about 50% efficient, which makes no sense whatsoever. It seems like with the kind of money people are willing to putting flashlights on here, it should be possible to get higher-quality Aluminized surfaces (which can be well over 90% reflective), or even some sort of total-internal-reflecting optics like projector headlights.
there was a long thread discussing that... I can't find it right now..
the jist is that, a filament emits light in all directions, the problem is, the bulb is shoved through a hole in the bottom of the reflector, so a "cone" of light emitted downward towards that hole is lost, that accounts for about 15-20% of the light loss in most reflector configurations. another 10-20% loss from the reflectivity not being "perfect" on the surface of the cone, and about 1-5% loss through the window..
when you load an LED into the base of a reflector, you loose a lot less, efficiency is more like 85-90% because LEDs emit light on a "half-plane" so to speak. so they don't loose light out the back of the hole.