Related Clues:

• Fluorescent tube gas
• It lights up the night
• Balloon fill
• About 1% of the Earth's atmosphere
• Glower
• Like highlighter colors
• Element number 54
• Fluorescent
• Times Square light
• Sign filler
• Lead source
• Liquid ___ (refrigerant)
• Light fill
• Light on Broadway
• Marquee material, perhaps