Modding with SSC... brighter, or longer runtime?

I have noticed that nearly all my headlamps use a Luxeon star. I am thinking of swapping them with SSC LED's. I know that one advantage of SSC or Cree over Lux is in efficiency; they can run either brighter with the same draw, or same brightness with extended battery life, or any mix in between. My question is, if I just swap out the star for an SSC star, without getting into power supply headaches, is there any way to know if my light will be brighter with less runtime, or equivalent brightness with greater runtime, or some middle-of-the-road compromise? Brighter would be my reason for the swap (so I can then diffuse the spill with GLAD Press'n Seal without compromising throw) but then I have concerns that my 3AAA headlamps would still offer useable runtime if the SSC efficiency advantage goes all toward brightness. My 3AA headlamp I think would give decent runtime in that case. From the SSC star swaps I have done on my Elektrolumens 2D Blaster and XM-3, I have seen both a nominal increase in current draw (reduced runtime) combined with increased brightness. Is there any rule of thumb which dictates what one will see from such a swap if one does not **** with the power supply, or does it depend on the type of power supply regulation, if any? Thanks.

A perfect result depends on different factors. Perfect heatsink, good regulation, Led with the correct vf and a stabile power supply.
The AAA-cells are very weak in efficiency and I found also weak heatsinks in my headlamps.
At first I would measure the datas at your existing light. How hard will the Led be driven at the highest level, what Voltage you'll see at the Led.
Then decide, which SSC or Cree will fit with the right vf. The lower the vf, the longer the runtime, but improve the heatsink if possible. If you are in doubt, go with a higher vf in view of reliability and lifespan of the Led.
For sure you should gain brightness and perhaps more runtime with the perfect match.

Best regards

____
Tom

Depends on the type of regulator the headlamp has, if any.

If the headlamp has a constant current regulator, then you will get the same runtime, but brighter.

If the headlamp has no regulation, and the new LED has a lower Vf than the old one, then you will have a very much brighter lamp and shorter runtime.

If the headlamp has no regulation, and the new LED has a higher Vf than the old one, then you will have a brighter lamp and longer runtime.

Toshi