「明るくなってきた」なので、現在進行形のis 動詞+ingを使ってください。
"It's getting bright outside." です。ここで "getting" は「〜になってきた」を意味します。さらに、"bright" は「明るい」を意味しています。
下記の例文の紹介しますね。
I sometimes see the sunrise on my way home after working nights.
「夜勤後の帰宅時に、時々日の出を見ます。」
夜勤のお仕事ご苦労様です。
daylightは「日光・昼間」の意味もありますが、この状況では「夜明け」という意味となっています。この表現にdaylightをdawnに変えても使えます。
例) It's already daylight(dawn) outside when I go home from work.
(仕事から帰宅する時ににもう夜明けになっている。）
If you want to comment on the sky during your commute back to your house, you could say "by the time I finish my night shift, the sun is already starting to rise."
You spent the evening chatting with your travelling companion around the camp fire.
You slept in the forest but were woken early in the morning by the sound of the dawn chorus and the howling wolves.
You decided to make an early start and saddled up the horses.
Beyond the covering of foliage you could see the first signs of daylight.
You comment to your partner:
"Dawn's coming."
"I guess so."
when spring is getting nearer we have
increased daylight hours.
We can express this by saying
"the days are getting longer now".
or
"it's brighter outside now".
or
"The mornings are getting lighter".
春が近づいてくると日が長くなります。
これを以下のように表現することができます。
"the days are getting longer now".
日が長くなってきています。
"it's brighter outside now".
外が明るいです。
"The mornings are getting lighter".
朝がより明るくなってきました。
The noun 'dawn' means the light that shows just before sunrise. It is the first sign that the night is ending and that day is about to break, what is referred to as 'day break'. This happens often if one has been deeply engrossed in his/her work right through the night. One hardly notices how fast time flies.
So, you may say:
It appears that dawn has broken.
or
Its daylight already.
名詞 'dawn' は、日の出の前の明るくなる様子を意味します。夜明けのサインとされていて、 'day break'（夜明け）とも言われます。
夜通し集中して仕事をしているときに経験することです。時間が早く過ぎていることにほとんど気づかないことでしょう。
例：
It appears that dawn has broken.
夜が明けた。
It's daylight already.
もう朝の光だ。
We can either talk about it being, "bright," or talk about the fact that there is, "daylight," outside to mention that the sun is starting to come up. We can also talk about this in terms of, "working through the night," to express that we worked the entire night to the point where the daylight is coming.
日本 
アメリカ合衆国 
カナダ 
イギリス 
南アフリカ 
