Which illumination method is used to examine doubly refractile particles?

• A. Polarized light
• B. Brightfield
• C. Phase contrast
• D. Darkfield

Answer: (A)

Doubly refractile items are birefringent, meaning they split light into two rays that travel at different speeds. Polarized light microscopy uses a polarizer and an analyzer so these two rays interfere and produce characteristic interference colors that change with the crystal’s thickness and orientation. This makes birefringent particles visually distinct—bright and color-rich—compared with non-birefringent material. Other illumination methods don’t specifically reveal this birefringence: brightfield shows absorption, phase contrast highlights phase shifts to enhance edges of transparent structures, and darkfield visualizes scattered light. Therefore, polarized light is the best way to examine doubly refractile particles.