Many Songs.

Here is Sibelius
Here's Beethoven Concerto
Here's Mendelhson 1

Light and Cloud

                                            A Contrary

This is a painting called, "God Judging Adam.
It had a very bright background full of Light, but the chariot of God has a dark cloud all around it;

---

This one is called Glad Day

From the King James Bible; Psalms 118, verse 24:

"This is the day which the LORD hath made; we will rejoice and be glad in it."

But our interest here is the Contrary of Light and Cloud.

---

We were driving south from Washington, D.C. under a heavy cloud; when we came to the

south end of Virginian, there was a very dramatic line of the clouds; we drove into

N.C. and the clouds were completely gone.

In the Beginning God said, "let there be light". The world began with Light.
1:27 So God created man in his own image
2:7 And the LORD God formed man of the dust of the ground, and breathed into
his nostrils the breath of life; and man became a living soul.

We could say that the Living Souls were full of Light; they came down from above (created by God)
But the Light became Cloudy when Eve (and then Adam) ate the forbidden fruit.

---

In the Sea of Time and Space The nymphs, with their buckets filled with Light came into the Water
(which makes Clouds). In due course they may perhaps come back out of the Sea, giving up mortal life to become Immortals.

This is the primary myth of the Bible (and of William Blake), a descent and then an ascent.

Clouds is a metaphor the earthiness, for sin, for misfortunes of every sort.

Church people sing: : "O they tell me of the Unclouded day"

And "Melt the Clouds of sin and sadness, drive the dark of doubt away."

And secular people may sing "O give me a home where the skies are not cloudy all day".

If you want more on Light, look at this post.

Vala is generally pictured as the Evil or Fallen female.  This passage is essentially about Vala
when she has suborned Jerusalem in the dark days of clouds over the Light:

"A pillar of smoke writhing afar into Non-Entity, redounding

Till the cloud reaches afar outstretch'd among the Starry Wheels
Which revolve heavily in the mighty Void above the Furnaces

O what avail the loves & tears of Beulahs lovely Daughters
They hold the Immortal Form in gentle bands & tender tears       
But all within is open'd into the deeps of Entuthon Benython
A dark and unknown night, indefinite, unmeasurable, without end.
Abstract Philosophy warring in enmity against Imagination
(Which is the Divine Body of the Lord Jesus. blessed for ever).
And there Jerusalem wanders with Vala upon the mountains,        
Attracted by the revolutions of those Wheels the Cloud of smoke
Immense, and Jerusalem & Vala weeping in the Cloud
Wander away into the Chaotic Void, lamenting with her Shadow
Among the Daughters of Albion, among the Starry Wheels;
Lamenting for her children, for the sons & daughters of Albion"

(Plate 5 of Milton; Erdman 148)

Blake's poetry makes continuous use of these symbols of Light,Clouds, and Darkness.