Nelson and Bugbee compared the efficiency of 22 lighting fixtures and found that the best light emitting diode fixtures—commonly known as LEDs—and the best high pressure sodium fixtures—often used in street lamps—are equally efficient. These two types of fixtures, however, provide optimum light for plants in significantly different ways.
USU Crop Physiology Lab, "USU Researchers Find That Lighting Efficiency for Plant Growth has doubled in Six Years" (2014). Controlled Environments. Paper 6.