Final answer:
Besides direct light from a source, reflected light must also be measured, particularly for assessing brightness. Luminous flux helps compare the brightness of different bulbs. The electromagnetic spectrum includes all types of electromagnetic radiation beyond visible light.
Step-by-step explanation:
The type of light that must be measured, besides light coming directly from a source, is reflected light, which is essential when assessing brightness or illumination of objects not emitting their own light. In the context of selecting an energy-saving light bulb, such as a compact fluorescent lamp or an LED bulb, it is important to measure the luminous flux in lumens to ensure that the new bulb provides the same brightness as the old incandescent bulb. Additionally, when studying electromagnetic radiation, we consider not just visible light but the entire electromagnetic spectrum, which includes a range of wavelengths from radio waves to gamma rays, important for comprehensive scientific analysis.