Neon signs are made from glass tubes with the inside coated with a phosphorescent powder coating. Different coloured sections of glass tube can be joined together to produce different coloured sections as shown in the picture. The glass tube is filled with a purified argon gas mixture and the gas ionized by a high voltage between the ends of the tube with electrodes. Neon gas can be used in a clear glass tube and has a yellowish orange colour. The “hidden” sections are black.
https://en.wikipedia.org/wiki/Neon_sign
Neon signs became expensive due to environmental restrictions but are still in use with many heritage projects keeping the craft going. Alternative materials such as El Wire, Neon Flex and LED Tape are cheaper and easier to use, but do not have the brightness of Neon. These cheaper alternatives still require artistic craftmanship.
This Comparison of Various Light Sources Output Efficiency, Color Range, & Lifespan does not compare Light Output http://www.neonshop.com/Tech/compare.html
Neon Lighting states Lumen output from neon tubes is 500 lumens per foot. Neon Tubes generally come with four (4) sizes in diameter 9mm, 10mm, 12mm and 15mm. Any size above 15mm are called Cold Cathode Tubes . http://neon-lighting.com/neon.htm#:~:text=Lumen%20output%20from%20neon%20tubes%20is%20500%20lumens%20per%20foot.&text=and%2015mm.,are%20called%20Cold%20Cathode%20tubes.
Neon Design has a Light Output Chart for Neon Sign Tubing http://neondesign.com/technical-information/light-output-chart/