Possible Clues:

• Could this throw light on teacher returning during the afternoon?
• Certain decorative paperweight
• Solid shape, proper round sphere, primarily
• Spectrum former
• Reflector in some telescopes
• Glass that makes a rainbow
• 'Dark Side of the Moon' album image
• Light refractor, or, when broken into three parts, a hint to the theme answers
• Raindrop in the sunlight, e.g
• It breaks light up into rainbow's colours