I'm not sure how small the eye sockets are on the whistle skulls... but LEDs come in a variety of sizes. One of the most common in terms of Radio Shack purchases (and power lights on computers etc) are the 5mm size, but presumably you'd want smaller.
Just need to get the voltage correct for the LEDs. A pair of red LEDs in parallel will probably need to be in series with a small resistor with a pair of batteries in series (AAA will work here) depending on the color. This'll maximze the battery life.
With small red LEDs you can probably get away with a single 1.5V battery and no resistor. These LEDs prefer 1.7V usually, but 1.5V should be above that "starting" voltage**. With other colors, you'll need to check the voltage of the LEDs you buy. Many amber and green ones expect about 2.2V. Frequently blue LEDs expect 2.5-5V. This is why I was saying a second battery might be necessary, and then add a resistor.
**(LEDs require a certain minimum voltage before they start illuminating. Once they have that, the voltage can be backed off to dim them, but they won't come on if started at the low voltage).
Here's a good link for calculating necessary resistances:
http://metku.net/index.html?sect=view&n=1&path=mods/ledcalc/index_eng
Just need to get the voltage correct for the LEDs. A pair of red LEDs in parallel will probably need to be in series with a small resistor with a pair of batteries in series (AAA will work here) depending on the color. This'll maximze the battery life.
With small red LEDs you can probably get away with a single 1.5V battery and no resistor. These LEDs prefer 1.7V usually, but 1.5V should be above that "starting" voltage**. With other colors, you'll need to check the voltage of the LEDs you buy. Many amber and green ones expect about 2.2V. Frequently blue LEDs expect 2.5-5V. This is why I was saying a second battery might be necessary, and then add a resistor.
**(LEDs require a certain minimum voltage before they start illuminating. Once they have that, the voltage can be backed off to dim them, but they won't come on if started at the low voltage).
Here's a good link for calculating necessary resistances:
http://metku.net/index.html?sect=view&n=1&path=mods/ledcalc/index_eng
