[quote postid="4362444" user="andrelook"]The right way to say this is,
Nearly all new quality flashlights use a circuit to run the LED. What this means is that no matter if you use 2 x 1.5 = 3.0 volts or a 3.7 volt lithium cell the output to the led lamp will be the same .. so that you get the same light output. If you see a difference in the light output when you use different batteries then you have a flashlight with no circuitry and it is a cheap design.
The reason for using a circuit is so that the output stays the same no matter the battery condition. Circuits also get the most power out of the battery as possible.
If you're interested the circuits are called a buck or boost circuit. They use a transistor switch and coil transformer to boost or drop (buck) the voltage from the battery(ies). The circuits are about $2 if you buy them separately at dealextreme or other sites online. You can make your own flashlight or led output lamp easily with battery, the circuit, and a lamp. You need to put it into something of course. Sites, like DX above, sell flashlight cases too.
This product, I suspect, does not have a circuit. That's why they use D cells. The output of a D cell is even over a long time .. and so a flashlight can work in the correct range for the led bulb for a long time. The downside is that 1.D cells are expensive compared to using rechargeable AA batteries. Without a circuit you'll see a drop off of light for 10 20 or more hours at the end of the D cell life. This isn't acceptable when the initial output, from the flashlight, is 160 lumen to begin with. A 100 watt regular incandescent lamp is 1300 lumen (about). 1/10 of that is about the same as a 10 watt incandescent bulb. This is quite low light output. It's enough to see in a room but you can get 2x the output for the same $10 price on ebay or any of the Chinese sites using a circuit, AA rechargeable batteries.
The only good about this deal is that you get a large flashlight 'case' which you can modify later. And you get a large flashlight case.. which you might prefer over something small. And it's woot so you know you'll get it fast and in good condition. I suppose all that's worth $10