Possible Clues:

• Illumination used for advertising
• Elemental luminosity?
• Fluorescent lamp
• It's quite bright, Noel, blending in from dusk to dawn
• Elementary clue used in advertising, for instance
• Advertising sign, perhaps
• Nighttime advertising sign, maybe
• Tubular fluorescent lamp
• Bar magnet?
• Source of illumination one badly needed, left in dark