Here's why:

* Brightness: Halogen lamps are very bright, providing the intense light needed to illuminate the document being copied.

* Color Temperature: Halogen lamps have a color temperature close to daylight, ensuring accurate color reproduction in the copy.

* Durability: They are relatively durable and have a longer lifespan compared to other types of light sources.

* Compactness: Their size makes them suitable for fitting within the compact design of copy machines.

While some newer models might use other technologies like LED lamps, halogen lamps remain the most common type used in traditional copy machines.