阳光 (yángguāng) means "sunlight" or "sunshine." It is used to describe the light and warmth from the sun, and can also be used figuratively to describe a bright, cheerful, or optimistic personality.
今天阳光真好,我们出去走走吧。
Jīntiān yángguāng zhēn hǎo, wǒmen chūqù zǒuzou ba.
The sunshine is so nice today — let's go for a walk.
温暖的阳光照进了房间。
Wēnnuǎn de yángguāng zhàojìnle fángjiān.
Warm sunlight shone into the room.
她是个很阳光的女孩,总是笑着。
Tā shì gè hěn yángguāng de nǚhái, zǒngshì xiàozhe.
She is a very sunny girl who is always smiling.