Photobiology & Light Science Flashcards

What is the optical window of tissue, also called the 'therapeutic window'?

Answer: 600–1100 nm range where light penetrates tissue most effectively

The therapeutic window (600–1100 nm) is where tissue absorption and scattering are low enough to allow significant light penetration for clinical effects.

What is the primary effect of reactive oxygen species (ROS) produced in small amounts during PBM?

Answer: Act as signaling molecules that trigger cellular repair and proliferation

Low-level ROS generated during PBM serve as secondary messengers that activate signaling pathways promoting cellular survival, repair, and growth.

Which effect does blue light (400–500 nm) have on Propionibacterium acnes bacteria?

Answer: Excites porphyrins within the bacteria, producing toxic singlet oxygen

Blue light activates porphyrins naturally present in P. acnes bacteria, generating singlet oxygen that destroys the bacteria through photooxidation.

What term describes the scattering of light in multiple directions as it passes through tissue?

Answer: Diffuse reflectance

Diffuse reflectance occurs when light scatters in multiple random directions as it interacts with the heterogeneous structures within biological tissue.

Which molecule absorbs green light (around 540 nm) and is relevant to vascular light therapy treatments?

Answer: Oxyhemoglobin

Oxyhemoglobin has strong absorption peaks around 540 nm and 577 nm, making green light effective for targeting superficial blood vessels.

What does the term 'coherence' mean when describing laser light used in light therapy?

Answer: All photons travel in phase with the same wavelength and direction

Coherence in laser light means all photons are in phase (temporal coherence) and travel in the same direction (spatial coherence), producing a highly organized beam.