🔍 Key Concepts

• Review how an incandescent bulb produces light (heated filament vs. gas discharge). • Compare which fixtures in the illustration use a filament only versus a discharge tube with ballast. • Notice which lamp circuit does not require a ballast or igniter to operate from the AC supply.

💭 Think About

• Looking at each labeled fixture A–D, which one shows a simple filament inside the glass envelope instead of an arc or discharge tube? • Which of the four circuits is directly connected to the voltage source without any special ballast, igniter, or transformer components? • Among MBF, SOX, and SON lamps, which types are known to be gas‑discharge lamps rather than incandescent? What does that leave as the incandescent option?

✅ Before You Answer

• Verify which diagram explicitly labels a wire filament as the light‑producing element. • Check which fixtures (B, C, D) mention components like ballast, igniter, or discharge tube—these are typical of gas‑discharge lamps, not incandescent bulbs. • Confirm that the remaining fixture matches the construction you’d expect for a standard incandescent lamp: screw cap, filament, support wires, and no external control gear in the circuit.