6.12: Activity 10

Integrated Human Anatomy and Physiology Lab Manual I: Fundamentals of Structure and Movement · LibreTexts

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    UV light and SPF (Sun Protection Factor)

    Ultraviolet light is invisible to humans, because it has shorter wavelengths than the light we can see. Within the Ultra Violet (UV) spectrum, there are two types of rays that can damage the DNA in skin cells and lead to skin cancer. It’s important to protect skin from both types:

    • UV-B rays cause sunburn and play a key role in developing skin cancer. A sunscreen’s SPF number refers mainly to the amount of UV-B protection it provides.
    • UV-A rays cause skin damage that leads to tanning as well as skin aging and wrinkles. The shortest wavelengths of UV-A rays also contribute to sunburn. It’s important to look for the words “broad spectrum” on a product’s label, which means it has ingredients that can protect you from UV-A as well as UV-B rays.

    What protects us from UV light? One strategy would be to avoid exposure to any type of sunlight. Since we cannot avoid sunlight while outdoors, we can physically or chemically block the sun. A wide variety of commercial sunscreens are available with Sun Protection Factors (SPF) ranging from SPF 2 to SPF 100. These lotions contain organic molecules that absorb UV light. Some materials, such as glass and plastic also absorb UV light, while still allowing visible light through.

    The SPF number is not a perfect measure of sun protection. The actual time it takes to burn depends on various factors, including the intensity of the sun, skin type, and how much sunscreen is applied. UV Beads are the perfect tool for understanding how solar radiation can be harmful and to recognize measures that can be taken to reduce the risks associated with exposure to sunlight. When we expose bare skin to sunlight, it will either burn or tan. UV radiation wavelengths are short enough to break chemical bonds in your skin tissue and, with prolonged exposure, your skin may wrinkle or skin cancer may occur.

    Materials and Equipment

    UV-sensitive beads, sunscreen lotions with various SPF ratings, sunblock, sunglasses, clear and opaque yellow/amber color plastic container (generally used in storage of medicines), small plastic bags, laboratory UV light.

    Safety Note - Your eyes should not be directly exposed to the indoor lab UV light source. No materials used in this experiment should be ingested.

    Personal protective equipment (PPE): lab coat, safety goggles

    Part A: Detecting UV light

    1. Place 6 to 8 UV-sensitive beads in two small plastic bags. These beads will turn color in the presence of UV light. The higher the intensity of UV light the stronger the color change.
    2. Make two bags: one labeled “Control” and one labeled “Experiment”.
      • Record the color of the beads when exposed to indoor light (lighting in the lab).
    3. The control bag will remain at your bench, and should be used for comparison to color changes in experiment.
    4. Take the experiment bag outside, in an area of direct sunlight.
      • Record the color of the beads after 10 seconds of exposure to outside sunlight.
    5. Find a shaded area (example: under a tree or in a corridor).
      • Record the color of the beads in shade.
    Table \(\PageIndex{1}\): Color Change in UV-Sensitive Beads Under Different Lighting Conditions
    Condition Color of Control Beads Color of Experiment Beads
    Indoor Light
    Sunlight
    Shade

    Part B: Absorption of UV Light by SPF lotions

    1. Place 6 to 8 UV-sensitive beads into a small plastic bag; make three bags, label with the SPF numbers. Note the color of the beads under indoor lighting.
    2. Add one small drop/dab of each lotion onto each bag. Lightly coat/spread to cover one side of the bag. Allow lotion to dry. Bring the bags to a laboratory UV light setup. Leave bag for 10 seconds. Look into the front of the setup (but not directly at the light) to record the color of the beads under UV light.
    3. Empty the beads into beaker at front bench. Discard coated plastic bags.
    Table \(\PageIndex{2} \): Effect of SPF Lotions on UV-Sensitive Bead Color Change
    Condition Color of Control Beads Before UV Color of Beads Under UV
    SPF 90
    SPF 70
    SPF 50
    SPF 15
    Yellow Bottle

    Questions

    1. What is the difference between UV-A, UV-B, and UV-C light?
    2. What is the purpose of an experimental control? Give one specific example of a control used in this experiment.
    3. From your data in Part B, do higher SPF ratings provide more protection from UV light?
    4. Imagine the Los Angeles Times has reported a UV Index of 6.5 today. Given this level of UV exposure, which is considered high, how might you adjust your plans to take care of your skin and overall health?

    This page titled 6.12: Activity 10 was last modified on Tue, 01 Sep 2026 01:45:37 GMT and is shared under a CC BY-NC 4.0 license and was authored, remixed, and/or curated by Lakshmikanta Sengupta and Susmita Sengupta.