Make a small flashlight with LED lights
I suggest you use the high-power 1W lamp, it will be relatively light, if the demand is not high with a can lighting.
If simple, buy a 1W or 3W lamp, a series resistor and slightly on the battery is good, the cement resistance of 12 ohms around 0.25W, 3 batteries of about 4.5V, the general lamp voltage of about 3.3V, can not be added directly on the battery. Standard can be two batteries plus step-up circuit approach, but you do simple, there is no need to be so troublesome.
The simplest solution: with a bright diode series together, the diode's maximum burning current and pressure drop to be found, according to the power and diode voltage drop to calculate the appropriate current limiting resistance, to ensure that the current is not big. Common battery, rechargeable battery, small lead acid battery can be used in power supply. If the supply voltage is low, the shunt scheme may be selected, but one that is broken easily leads to other overcurrent damage. The key is what you have in your hand. That's what DIY is about.
