And I saw that wisdom excels folly as light excels darkness.
-Ecclesiastes 2:13

Your word is a lamp to my feet and a light to my path.
-Psalm 119:105

The unfolding of your words gives light; it imparts understanding to the simple.
-Psalm 119:130

But the path of the righteous is like the light of dawn, which shines brighter and brighter until full day. The way of the wicked is like deep darkness; they do not know over what they stumble.
-Proverbs 4:18-19

This is the message we have heard from Him and announce to you, that God is Light, and in Him there is no darkness at all. If we say that we have fellowship with Him and yet walk in the darkness, we lie and do not practice the truth; but if we walk in the Light as He Himself is in the Light, we have fellowship with one another, and the blood of Jesus His Son cleanses us from all sin.
-1 John 1:5-7

   Jesus Christ is the Light that has been revealed to us from God:

In Him was life, and the life was the Light of men. The Light shines in the darkness, and the darkness did not comprehend it. There came a man sent from God, whose name was John. He came as a witness, to testify about the Light, so that all might believe through him. He was not the Light, but he came to testify about the Light.
-John 1:4-8

For God, who said, “Light shall shine out of darkness,” is the One who has shone in our hearts to give the Light of the knowledge of the glory of God in the face of Christ.
-2 Corinthians 4:6

Several times throughout the Gospel of John, Christ even
refers to Himself as the ‘Light’:

Then Jesus again spoke to them, saying, “I am the Light of the world, he who follows Me will not walk in the darkness, but will have the Light of life.”
-John 8:12

“I have come as Light into the world, so that everyone who believes in Me will not remain in darkness.”
-John 12:46

“This is the judgment, that the Light has come into the world, and men loved the darkness rather than the Light, for their deeds were evil. For everyone who does evil hates the Light, and does not come to the Light for fear that his deeds will be exposed. But he who practices the truth comes to the Light, so that his deeds may be manifested as having been wrought in God.”
-John 3:19-21

So Jesus said to them, “For a little while longer the Light is among you. Walk while you have the Light, so that darkness will not overtake you; he who walks in the darkness does not know where he goes. While you have the Light, believe in the Light, so that you may become sons of Light.” These things Jesus spoke, and He departed and hid Himself from them.
-John 12:35-36

Notice the contrasting statements Jesus uses about light & darkness in the passages above.

Scripture testifies that Jesus Christ is the spotless Lamb of God, in whom was neither sin nor deceit:

You know that He appeared in order to take away sins, and in Him there is no sin.
-1 John 3:5

He made Him who knew no sin to be sin on our behalf, so that we might become the righteousness of God in Him.
-2 Corinthians 5:21

For we do not have a high priest who cannot sympathize with our weaknesses, but One who has been tempted in all things as we are, yet without sin.
-Hebrews 4:15

how much more will the blood of Christ, who through the eternal Spirit offered Himself without blemish to God, purify our conscience from dead works to serve the living God.
-Hebrews 9:14

but with the precious blood of Christ, like that of a lamb without blemish or spot.
-1 Peter 1:19

For to this you have been called, because Christ also suffered for you, leaving you an example, so that you might follow in His steps. He committed no sin, neither was deceit found in His mouth.
-1 Peter 2:21-22

And they made his grave with the wicked and with a rich man in his death, although he had done no violence, and there was no deceit in his mouth.
-Isaiah 53:9

If we are unwilling to embrace Christ and accept Him as the Light, i.e. by disagreeing with His teachings, denying His nature, or disobeying His commands, we are actually saying that He is darkness, and that we have the true light already.
And we see that this is exactly what the Pharisees do in Matthew chapter 12:

Then a demon-oppressed man who was blind and mute was brought to Him, and He healed him, so that the man spoke and saw. And all the people were amazed, and said, “Can this be the Son of David?” But when the Pharisees heard it, they said, “It is only by Beelzebul, the prince of demons that this man casts out demons.”
-Matthew 12:22-24

By accusing Jesus of casting out demons by the prince of demons, they are saying to Jesus, “You are in darkness, & we are in the light.” They are calling their darkness light, and the true light which is Christ, darkness.
What is it called when someone thinks that they are in the light when they are actually in darkness?
Deception.
To be deceived is to be convinced that you are right, when in fact you are wrong.

In John chapter 7, the Pharisees refer to those believing in the teachings of Jesus as being deceived:

The Pharisees answered them, “Have you also been deceived? Have any of the authorities or the Pharisees believed in Him?”
-John 7:47-48

They are essentially implying that they themselves are the standard of light, & since none of them have believed in Him, He must be darkness.
Jesus warns of confusing darkness with light & light with darkness:

“The eye is the lamp of the body. So, if your eye is healthy, your whole body will be full of light, but if your eye is bad, your whole body will be full of darkness. If then the light in you is darkness, how great is that darkness!”
-Matthew 6:22-23

“Your eye is the lamp of your body. When your eye is healthy, your whole body is full of light, but when it is bad, your body is full of darkness. Therefore be careful lest the light in you be darkness.”
-Luke 11:34-35

The prophet Isaiah warns of this also:

Woe to those who call evil good, and good evil, who substitute darkness for light and light for darkness, who substitute bitter for sweet and sweet for bitter!
-Isaiah 5:20

In John chapter 9, after Jesus heals a man who had been born blind, the Pharisees question him about the experience:

“Never since the world began has it been heard that anyone opened the eyes of a man born blind. If this man were not from God, He could do nothing.”
They answered him, “You were born in utter sin, and would you teach us?” And they cast him out.
Jesus heard that they had cast him out, and having found him He said, “Do you believe in the Son of Man?”
He answered, “And who is He, sir, that I may believe in Him?”
Jesus said to him, “You have seen Him, and it is He who is speaking to you.”
He said, “Lord, I believe,” and he worshiped Him.
Jesus said, “For judgment I came into this world, that those who do not see may see, and those who see may become blind.”
Some of the Pharisees near Him heard these things, and said to Him, “Are we also blind?”
Jesus said to them, “If you were blind, you would have no guilt, but now that you say, ‘We see,’
your guilt remains.”
-John 9:32-41

Additional references from Scripture on the topic of darkness and light:

‘rescuing you from the Jewish people and from the Gentiles, to whom I am sending you, to open their eyes so that they may turn from darkness to light and from the dominion of Satan to God, that they may receive forgiveness of sins and an inheritance among those who have been sanctified by faith in Me.’
-Acts 26:17-18

The night is far gone; the day is at hand. Therefore let us cast off the works of darkness and put on the armor of light.
-Romans 13:12

Do not be unequally yoked with unbelievers. For what partnership has righteousness with lawlessness? Or what fellowship has light with darkness?
-2 Corinthians 6:14

For such men are false apostles, deceitful workers, disguising themselves as apostles of Christ.
No wonder, for even Satan disguises himself as an angel of light. Therefore it is not surprising if his servants also disguise themselves as servants of righteousness, whose end will be according to their deeds.
-2 Corinthians 11:13-15

For this you know with certainty, that no immoral or impure person or covetous man, who is an idolater, has an inheritance in the kingdom of Christ and God. Let no one deceive you with empty words, for because of these things the wrath of God comes upon the sons of disobedience.
Therefore do not be partakers with them; for you were formerly darkness, but now you are Light in the Lord; walk as children of Light (for the fruit of the Light consists in all goodness and righteousness and truth ), trying to learn what is pleasing to the Lord. Do not participate in the unfruitful deeds of darkness, but instead expose them.
-Ephesians 5:5-11

For He rescued us from the domain of darkness, and transferred us to the kingdom of His beloved Son, in whom we have redemption, the forgiveness of sins.
-Colossians 1:13-14

But you are a chosen race, a royal priesthood, a holy nation, a people for His own possession, that you may proclaim the excellencies of Him who called you out of darkness into His marvelous light.
-1 Peter 2:9

On the other hand, I am writing a new commandment to you, which is true in Him and in you, because the darkness is passing away and the true Light is already shining. The one who says he is in the Light and yet hates his brother is in the darkness until now. The one who loves his brother abides in the Light and there is no cause for stumbling in him. But the one who hates his brother is in the darkness and walks in the darkness, and does not know where he is going because the darkness has blinded his eyes.
-1 John 2:8-11

I saw no temple in it, for the Lord God the Almighty and the Lamb are its temple. And the city has no need of the sun or of the moon to shine on it, for the glory of God has illumined it, and its lamp is the Lamb.
-Revelation 21:22-23