Most commercially available LEDs have an epoxy-drop lens above the PN junction — the light-emitting element. These LEDs suffer from the same problem as a torch: They give a light spot with nonuniform brightness. The problem can be eliminated by changing the LED into a (semi) point-light source. Start with red, green, and blue LEDs that are encased in clear plastic.³ Using a hacksaw, carefully saw off the part of the LED body that makes the lens. Make sure that you do not cut too close to the PN junction (1 mm away is OK). If we want to make light propagate out from the plastic without being scattered by scratches, we have to brush and polish the sawed surface. Use fine water sandpaper starting from lower grades (such as grade 600) and finishing with higher grades (grade 1200). After this you have to polish the surface with an abrasive polishing paste (a white toothpaste also works well) until the surface looks clearly transparent. Repeat this procedure with all three LEDs.