My avatar is "Hikari", as calligraphed by the founder of Aikido, Morihei Ueshiba. It's the same hikari/hikaru as Hikki's. The meaning is "Light".

The next bit is in Japanese. If you're not using an Apple Mac (which can recognise Japanese automatically) you'll need to get out your Windows CD and install the East Asian languages and reboot to see the next bit.

From the dictionary:
光 [ひかり: HIKARI]  light.
光る [ひかる: HIKARU]  to shine, to glitter, to be bright.

Utada Hikaru as written in her stage name: 宇多田ヒカル
Utada Hikaru as it would appear in her family register (before marriage): 宇多田光
So now you can probably guess that the song "Hikari" is about herself.

Hikari in a large font:

光