Shemos 10:23 They saw not one another, neither rose any from his place for three days; but all the children of Israel had light in their dwellings.
Rav Levi Yitzchak of Berditchev addresses the obvious question: If the Egyptians were smitten with darkness for the ninth plague, we should know by now that this plague did not affect the Jews. What is meant by the words “…the Jews had light…”?
I remember as a small boy, that I was told that there would be an eclipse of the sun the next day. As this was the first eclipse that my classmates and I were going to experience, we were taught how to prepare for it. Specifically, we were told that we must wear special eye protection in order not to become blinded by the light of the sun. To me this was a great puzzle, because I already knew that on a regular day, it was virtually impossible to look directly at the sun due to its blinding light. It was explained to me that this was part of the Wonders of Creation. Hashem built into our environment devices that protect us so that we should not be hurt. For example, a person who touches a hot object will feel the pain and immediately remove his hand, thereby preventing further damage. A person can also smell smoke before an actual fire and can take actions to protect himself. So too our eyes are protected from damage by the sun’s rays on a regular day – our eyelids close, tear-up, or we instinctively turn away. However, at the time of the eclipse where the strength of the sun is dulled by the moon in front of it, one can look directly at the sun – yet even this diminished light can be damaging to the eyes.
In a similar vein, the Gemora talks about different reactions to one event: The sun will heal righteous ones and burn the evil ones; the consequences of the same exposure will depend upon the person’s level. This could also be compared to prescription eye glasses: they will help a person who cannot see well, but will hurt the eyes of someone whose vision is normal.
The Berditchever Rav explains that the light of the Plague of Darkness is the light that was created in the beginning of time. The Medrash tells us after the sin of Adam HaRishon, people were not worthy of benefitting from that light, and it was put away for a better time. At certain times (e.g. Moshiach) that light will be exposed and cause different reactions in our world. What happened during the plague of darkness was exactly this: The light from Creation was exposed, causing damage to the Egyptians who were not on the level to appreciate it, and benefitting the Jews with extra light. However, this extra light did not benefit the unworthy Jews who perished during this plague.
As we ponder our connection to Hashem during these weeks of Shovevim, it is incumbent upon us to bolster our ruchnius level, so that we can let more light into our homes. Not only will we not be affected negatively from it, but we will bask in the glory that Hashem has shined onto us.