Optical thermometry offers great precision, repeatability, flexibility, and stability, hence providing performance advantages in non-contact temperature measurement. To assess its potential for controlling the temperature of steam cracking furnaces, ethane steam cracking experiments were carried out on pilot plant scale. The control performance of the pyrometer was found to be comparable to that of a weld-on type K thermocouple, the latter being representative of the industrial standard. The tested optical thermometer is suited as a sensor to measure tube metal temperatures of a steam cracking reactor coil, either inside or outside of the firebox. Due to its fast response time, optical thermometer temperature measurements help to prevent temperature overshoots, which have an adverse effect on the tube longevity and coke formation. Flexibility in positioning makes optical thermometry a viable alternative compared to conventional type K thermocouples. (C) 2019 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.