I impulse-purchased a LED conversion kit for the 3 D-Cell mag I've had on hand for years (DW calls it her "whacking stick" - I don't want to be on receiving end!). Anyway, I was quite taken aback by the change from the stock bulb. Installation was very easy, just unscrew and drop in. Light output is much whiter and more intense. I have no metrics for that, it is scrictly a qualatative measure from my perception.

While I'm sure that battery life is extended somewhat, I can't judge how much. Since we mostly use the light when out searching for DK (Dear Kitty) it does not receive enough use to drain the batteries.