In the theoretical part of my thesis, I present light spectra, luminous efficacy, as well as light sources and sensors used in my experimental work. In the experimental part of the thesis, I compare three sensors: a spectrometer measuring the light spectrum, a luxmeter measuring the light intensity, as perceived by the human eye, and a light meter measuring the light intensity in watts per square meter. To compare the sensors, I find the relation between the quantities they measure. With calibrated sensors, I calculate luminous efficacy by measuring power consumption of light sources, the angular distribution of the light, and the amount of the visible light they produce. I use a classic light bulb, an energy-saving light bulb, and green and white light emitting diodes.