How much larger is a Lightning Creeper's explosion radius compared to a regular Creeper?

The power of charged creepers is 6 (data from decompiled source code), 3/2 powerful than TNT, twice powerful than normal creepers. But I then realized there were two definitions of "explosion radius" (for blocks and for entities), so I updated the wiki for your clarification.

In a word, The blast radius in the air for blocks of charged creepers is 10.2, and the damage radius for entities of charged creepers is 12.

Doing some tests with a 0 explosion-resistant block (redstone wires), here's the area that various explosions took out:

• Creeper: 43
• TNT: 81
• Super Creeper: 161

Assuming the TNT is equal to "4" radius (which really means up to 7 according to the wiki...), then the Creeper explosion ("3" radius) should have taken out 81 * (3/4)^2 = 45, fairly close to what it should be, so the test doesn't give way-off results. Extending that to the super creeper, it's 81 * (x/4)^2 = 161, so x = 5.639, which isn't a very nice integer, but that suggests that the range is almost double a normal creeper, and significantly more than TNT.

Despite this test trying to figure out the explosion radius only, and while the redstone wires have 0 resistance, there is still some power taken away for every block that the explosion destroys. Stacking TNT will give a larger apparent blast radius in the grid of wires, but only up to a point, then nothing will change.

(If I can find an exact properties of the explosion I will edit the answer, but here are two pictures that show the size difference)

Charged Creeper Explosion:

Regular Creeper Explosion:

Source: Minecraft Forums

Do Lightning Creepers have a larger explosion radius than regular Creepers?

yes, by definition

Explosion radius: The distance from the center of a crater to the edge of a crater.

Blast Power^†: The Blast Power of an explosion determines its blast radius. TNT explosion has 4 power, creeper explosion has 3, fireball explosion has 1.

As we know, the blast power of the lightning creeper is greater than that of a normal creeper. This means that the crater produced by the explosion will be larger due to the way in which blocks are destroyed by explosions in minecraft.

You do have to compare apples to apples. A normal creeper in sand will have a larger crater produced than a lightning creeper in obsidian. Typically the blast radii are calculated with the distance at which a player can be damaged by a creeper with no blocks in between them.

_{† The blast power definition was taken from the Minecraft Wiki on Explosions}