Which of the following is not a main advantage of tungsten bulbs?

• A. 80% heat, 20% light
• B. Low cost
• C. Good color rendering
• D. Long life

Answer: (A)

Incandescent tungsten bulbs are valued for three practical points: low upfront cost, and good color rendering because they emit a continuous spectrum similar to sunlight, plus straightforward dimming. But they’re not efficient: most of the electrical energy is wasted as heat rather than light. The idea that the bulb produces about 80% heat and 20% light highlights this drawback rather than a benefit. That inefficiency is exactly why this option isn’t considered a real advantage. The other choices reflect true advantages (low cost and good color rendering), while longevity isn’t a strong suit of these bulbs, but the key takeaway here is that high heat relative to light is not an advantage.