What is inside a bulb-air or vaccuum and why?

Inside a traditional incandescent light bulb, the space is typically filled with an inert gas, such as argon, or it may be a vacuum. This environment prevents oxidation of the filament, allowing it to glow brightly without burning out quickly. In compact fluorescent and LED bulbs, different gases and materials are used to generate light, but the principle remains the same: reducing oxygen exposure enhances longevity and efficiency.