The first time you saw a blacklight you were probably fascinated and amazed. These lightbulbs with a dark purplish color caused your shirt, makeup, or teeth to glow brightly. You also may have seen a blacklight used to identify an invisible hand stamp or reveal an unseen image in a poster. What is going on? While only a small portion of the light emitted by a blacklight is visible, the blacklight shines brightly in the higher energy, ultraviolet (UV) range that is beyond our visible range. When a material absorbs invisible UV light then re-emits lower energy, visible light, the material appears to glow through the process of fluorescence while the other, surrounding materials remain dark. Because many materials fluoresce and glow brightly under UV light, a blacklight is a valuable tool to detect counterfeits, to find leaks, and to investigate crime.
Legal currency contains fluorescent markings that are difficult to counterfeit. A blacklight can quickly and easily determine if a bill is real or fake. Blacklight can also be used to detect art forgeries since modern paints generally contain materials that fluoresce while older paints do not. Many body fluids fluoresce when exposed to blacklight and this allows crime scene investigators to quickly scan a room for evidence. Stubborn gas leaks can be found by mixing a fluorescent material with the gas, then using a blacklight to trace the line and find the leak. In all these cases, blacklight makes the invisible visible.
J.C. Ryle observed that sin never announces itself to us with its full intentions. This adage may be especially true for our hidden and secret sins. While God sees and knows everything, we may try to hide our sins from others (hypocrisy) or we may not clearly see our own sinfulness (self-delusion). Our invisible sins still damage us spiritual and harm the people around us. Our sin may cause God to not answer our prayers. (Psalm 66) Any sinner can expect to reap what they sow. (Galatians 6) Our sin may impact others immediately or for several generations. (Exodus 20)
So how do we shine the light of the Gospel on our invisible sins? The first of Martin Luther’s 95 theses was, “when our Lord and Master Jesus Christ said, ‘Repent’, He willed the entire life of believers to be one of repentance.” If repentance and confession are a normal practice of our spiritual life, then we can more easily take an honest spiritual inventory when we read God’s Word, hear godly preaching, or spend time alone with God in prayer. Several times in the Psalms God’s people prayed for Him to “test me” or “search me” to reveal their hidden and secret sins. (Psalms 17, 19, 26, 139) We can pray words of a hymn, for example, “change my heart O God, make it ever true, change my heart O God, may I be like You.” When we allow other Christians to hold us accountable, we are accepting the deceitfulness of sin, the wickedness we are capable of, and the importance of repentance. It may help to remember that all our sins are “written in the books” that will be opened on judgment day. (Revelation 20) While repentance can be unpleasant and humbling, our gracious God has designed godly repentance to lead us to salvation and freedom from the penalty, presence, and power of sin in our lives. (2 Corinthians 7)