These could also be great on motorcycles since you really can't upgrade the alternator. I had seen a DOT legal LED headlamp assembly for motorcycles. Don't know if I'm going to go that far though. Probably only if i buy stuff like a heated seat and heated grips to extend my riding season. I have already upgraded the tail light to LED, so I already have some excess alternator output over stock.
Anything less than HIDs and you're wasting your time.
I'm not so sure about that. For example, HIR bulbs (such as these: http://store.candlepower.com/hirlighting.html ) are pretty nice. I know, as I have upgraded all four of my CRX's headlight bulbs (the two low beams, and the two high beams) to Toshiba HIR bulbs some time ago (I did the upgrade before the Phillips HIR bulbs were out, otherwise I might have gone with the even more energy efficient Phillips HIRs).
That upgrade didn't save any power (HIR bulbs are pretty much stock power/wattage as compared to the 9005/9006 bulbs they were replacing), but the upgrade made a HUGE difference in the light output (my lows are just under twice as bright as stock, and the low-high HIR combo is around 3x the stock brightness). And unlike many HID kits, my HIR bulbs give a nice "warm white" light (I seem to recall they were somewhere around 3400K, but that's just from memory). And since HIR bulbs get the brightness from better (more efficient) technology (vs some bulb makers that over-drive the bulb to get that efficiency), my HIR bulbs have close to the lifetime rating of the stock 9005/9006 bulbs they replaced!
Back to the OP's post/question:
The Amazon link does say that those bulbs are 47watts. And since stock 9006 bulbs are 55watts, that would be a savings of 8 watts per bulb (or a little over 1 amp total power savings). That isn't huge, but it might be enough to be noticeable. OTOH some other 9006 bulbs were already slightly less than 55 watts anyway, so (depending upon which bulb you were comparing against), the savings might be even smaller than the initial analysis would suggest.
However, there also seem to be other key pieces of info missing. And without that missing info, I personally wouldn't consider getting them. Specifically, I like to not only know what the power (wattage of the bulb) is, I also like knowing the answers to these questions:
1) How much light (lumen output) does the bulb have? You can sacrifice some light output to save power, but that lower light output could be a problem driving at night on a dark road. BTW: That's one reason why I so much like my HIR bulbs, because their light output is significantly larger than stock bulbs.
2) What is the expected bulb life? A bulb maker can get a little more energy efficiency out of bulbs by "over driving" the bulb. However, the trade-off of that approach, is that it has the side-effect of greatly shortening the lifetime of the bulb. Even with the extra bulb replacement costs, it may still be a "win" (cost wise) if the fuel savings is high enough. However, even if it is a "win", how many of us want to be constantly changing our headlights? OTOH it is also possible to not sacrifice bulb life at all, if sufficiently better technology is used. For example, my HIR bulbs have close to the lifetime rating of the stock bulbs they replaced. So we really need to know the lifetime rating of the bulb, in order to make an informed decision here.
3) What is the color spectrum of the bulb (i.e. how warm/cool is the white light)? I personally go for a more "warm white" light, as it produces less glare at night. In the case of my HIR bulbs, the color spectrum is an almost stock "warm white" color (I think it was somewhere around 3400K, but that is just from memory).
$30 hids in a pair of junkyard BMW halogen projectors. All the headlight you'll ever need with 35w per side. Padron my blurry camera. I have about $60 in the whole setup.
Previous to the hid i had another setup using brand new 90mm Hella H9 projectors with teh stock H9 bulbs. These are 65w. Really excellent light out put for a halogen bulb but it doesn't come close to HID. This setup set me back about $200 but that was a few years ago. The price of HIDs has come down to the point to where theres really no excuse for anything less.
The projector is really the critical component here. Reflectors are really outdated tech, even the very best ones.