Answer:
A Beaker is better.
Step-by-step explanation:
Sunlight radiation generates electromagnetic waves with different wave longs , when all the waves move together our eyes see white light but objects like a beaker made with glass can refract and separate the waves and show it in different colors.
A thermometer only measure temperature using a substance like Mercury, it changes its volumen with the increase or decrease of temperature and that change is shown in the instrument.