霓虹灯是一种内含气体的灯，通常用于广告招牌等用途。

“霓虹灯”是半英语音译。英语称为“neon lamp”（直译：氖灯）。“霓虹”发音近似于英语的“neon”并在汉语里有彩虹的含义。

霓虹灯通常为一条玻璃管，内含低压氖气或其他惰性气体，以微弱的直流或交流电经过管子而产生橙红色的光线。在交流电激发的霓虹灯，两个电极皆会产生光，而以直流电激发的霓虹灯，只有负极会产生光。此现象令霓虹灯可用以分辨直流与交流电电源，及分辨直流电的两极。

管内气体的实际成份为99.5%氖气及0.5%氩气，比纯氖气有较低的运作电压。

A neon lamp (also neon glow lamp) is a miniature gas discharge lamp. The lamp typically consists of a small glass capsule that contains a mixture of neon and other gases at a low pressure and two electrodes (an anode and a cathode). When sufficient voltage is applied and sufficient current is supplied between the electrodes, the lamp produces an orange glow discharge. The glowing portion in the lamp is a thin region near the cathode; the larger and much longer neon signs are also glow discharges, but they use the positive column which is not present in the ordinary neon lamp. Neon glow lamps are widely used as indicator lamps in the displays of electronic instruments and appliances.