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Lens Treatments and Coatings Flashcards

7 cards from real NOCE practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.

Read the first 7 Lens Treatments and Coatings flashcards as text

  1. An uncoated standard CR-39 plastic lens reflects approximately what percentage of incident light from each surface?

    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.

  2. Photochromic lenses typically activate in response to which type of radiation?

    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.

  3. What is the primary function of a hydrophobic coating applied over an anti-reflective coating?

    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.

  4. Which type of lens treatment is applied to create a reflective, mirror-like appearance on the front surface of sunglasses?

    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.

  5. Blue light-filtering lenses are designed to reduce transmission of light in which approximate wavelength range?

    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.

  6. How does high ambient temperature typically affect the performance of photochromic lenses?

    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.

  7. In a standard multi-coating stack applied to an ophthalmic lens, which coating is typically applied as the outermost (final) layer?

    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.