NOCE Lens Treatments and Coatings 2 — Questions and Answers
Question 1: An uncoated standard CR-39 plastic lens reflects approximately what percentage of incident light from each surface?
- 2–3%
- 8% (Correct answer)
- 12–15%
- 20%
Correct answer: 8%
An uncoated CR-39 lens reflects approximately 4% per surface (front and back combined approximately 8%), which AR coatings reduce to under 1% total.
Question 2: Photochromic lenses typically activate in response to which type of radiation?
- Ultraviolet (UV) radiation (Correct answer)
- Visible blue light only
- Infrared (IR) radiation
- Ambient temperature change alone
Correct answer: Ultraviolet (UV) radiation
Photochromic lenses are activated primarily by UV radiation, which triggers the reversible molecular change that causes darkening — this is why they often don't darken behind UV-blocking car windshields.
Question 3: What is the primary function of a hydrophobic coating applied over an anti-reflective coating?
- To prevent ultraviolet radiation from degrading the AR coating
- To repel water, oils, and smudges from the lens surface (Correct answer)
- To harden the lens and increase scratch resistance below the AR layer
- To reduce electrostatic charge that attracts dust particles
Correct answer: To repel water, oils, and smudges from the lens surface
A hydrophobic (water-repelling) top coat causes water and oils to bead up and roll off the lens surface, reducing smudging and making the lens easier to clean.
Question 4: Which type of lens treatment is applied to create a reflective, mirror-like appearance on the front surface of sunglasses?
- Polarized filter embedded in the lens substrate
- Flash or mirror coating deposited on the front surface (Correct answer)
- Photochromic molecular treatment throughout the lens
- Anti-reflective coating applied to the front surface only
Correct answer: Flash or mirror coating deposited on the front surface
A flash or mirror coating is a vacuum-deposited metallic layer on the front surface that creates a reflective appearance while reducing visible light transmission.
Question 5: Blue light-filtering lenses are designed to reduce transmission of light in which approximate wavelength range?
- 200–280 nm (UVC range)
- 380–500 nm (violet to blue visible light) (Correct answer)
- 500–600 nm (green to yellow visible light)
- 620–700 nm (red visible light)
Correct answer: 380–500 nm (violet to blue visible light)
Blue light lenses target the 380–500nm range, which includes high-energy visible (HEV) blue-violet light associated with digital screens and linked to potential retinal and sleep-cycle concerns.
Question 6: How does high ambient temperature typically affect the performance of photochromic lenses?
- They darken more rapidly at higher temperatures
- They achieve a consistently darker final state at higher temperatures
- They do not darken as deeply at higher temperatures, resulting in reduced performance (Correct answer)
- They permanently lose photochromic capability after repeated heat exposure
Correct answer: They do not darken as deeply at higher temperatures, resulting in reduced performance
Higher temperatures hinder the molecular transition in photochromic lenses, so they darken less on hot sunny days than on cool ones — a known limitation of photochromic technology.
Question 7: In a standard multi-coating stack applied to an ophthalmic lens, which coating is typically applied as the outermost (final) layer?
- Hard coat (scratch-resistant layer)
- Anti-reflective layers
- Hydrophobic/oleophobic top coat (Correct answer)
- UV-absorbing treatment
Correct answer: Hydrophobic/oleophobic top coat
The hydrophobic or oleophobic top coat is deposited last in the coating stack, sitting on top of the AR layers to repel water and oils from the outermost exposed surface.
NOCE Lens Treatments and Coatings 2
An uncoated standard CR-39 plastic lens reflects approximately what percentage of incident light from each surface?