Sunlight carries energy as electromagnetic radiation. A surface can reflect, transmit or absorb some of that radiation. Dark, matt surfaces tend to absorb a larger fraction of visible and infrared radiation than light, shiny surfaces. Absorbed energy increases the thermal energy store of the material. That can make a black shirt heat up more strongly in direct sunlight. The exact result also depends on fabric, airflow, thickness and how loose the clothing is. The same principles of absorption and emission are used when designing solar collectors, buildings and thermal equipment.

This is also a design problem. Cameras, glasses, screens, road signs and medical scanners all depend on controlling how electromagnetic waves are emitted, absorbed, reflected or refracted. A familiar object can therefore be a practical example of the same wave rules studied in class.

Waves transfer energy and information without transferring matter from source to receiver overall. Frequency tells us how many oscillations pass each second, wavelength is the spacing between matching points, and wave speed links them through v = fλ. Different frequencies interact with materials differently, which is why engineers can choose particular parts of the electromagnetic spectrum—or particular sound frequencies—for sensing, communication, heating or imaging.