NALMCO Certified Apprentice Lighting Technician (CALT) Practice Exam

Ultrasonic occupancy sensors detect changes in which type of waves?

1. Changes in reflected sound waves

2. Changes in background heat radiation

3. Changes in availability of daylight

4. None of the above

The correct answer is: Changes in reflected sound waves

Ultrasonic occupancy sensors operate by emitting ultrasonic sound waves, which are sound waves at a frequency higher than the upper limit of human hearing, typically above 20 kHz. These sensors continuously transmit these ultrasonic waves and then measure the time it takes for them to bounce back after hitting an object in the environment, such as a person or furniture. When an individual enters the detection zone of the sensor, their movement causes a change in the pattern of the reflected sound waves. The sensor detects these alterations in the returned sound waves, allowing it to ascertain whether the space is occupied or not. This principle enables ultrasonic sensors to be particularly sensitive and effective in various lighting and room configurations, even in spaces with obstacles that might block other forms of detection. The other options do not align with how ultrasonic sensors function. Background heat radiation pertains to infrared sensors, while the availability of daylight relates to photocells that detect light levels, not sound wave reflection. Thus, the focus on changes in reflected sound waves is what makes this choice the correct answer in the context of ultrasonic occupancy sensors.