Intensifying visible light to the point where it causes metal to spark or melt primarily depends on the intensity and duration of the light exposure, as well as the specific properties of the metal in question.
Visible light can indeed cause heating effects, and if the intensity is high enough, it can potentially cause metal to reach its melting point. However, achieving such high intensities with visible light alone can be challenging. Visible light sources, such as lasers, can produce intense beams, but they are typically not powerful enough to cause metals to spark or melt directly.
In contrast, microwave ovens operate at a frequency that is specifically absorbed by water molecules, causing them to vibrate and generate heat. The intensity of microwaves inside an oven is typically high enough to rapidly heat up the water molecules in food, but it is generally not concentrated or focused enough to directly cause metals to spark or melt.
To create the desired effects of sparking or melting metal using visible light, one would typically need to use other methods such as high-intensity lasers or intense light sources specifically designed for such applications. These methods often involve focused beams and specialized equipment to achieve the required energy levels.