electron-ray tube

[ ih-lek-tron-rey ]
/ ɪˈlɛk trɒnˌreɪ /

noun Electronics.

a small cathode-ray tube having a fluorescent screen on which the pattern varies with the voltage applied to the grid: used chiefly in radio receivers to indicate accuracy of tuning.
Also called electric eye.
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019