Since this word consists of a kanji with hiragana attached, you can bet that it will use the kun'yomi reading. You didn't learn that reading with this kanji, so here's a mnemonic to help you:
You have to remember the あか portion. What is あか in Japanese? It is "red." So, think of something that's really bright. Now, imagine it being totally red (aka あか). In Japan, the color red is associated with the sun, and the sun is pretty bright. If you can remember this you can also remember the reading of this word.
This room is bright.
Everyone at Tofugu is cheerful.
Your future is still bright, Grandpa.