Related Clues:

• Not to be seen at the rainbow's end
• The refrain of D cannot be seen in colour
• One can't ruddy well see it beyond the rainbow
• We're not able to see or find about how rare this is
• Fear you can't see rind like this
• An extreme case, where people don't normally see the light
• Ray, perhaps, uncovering rare find
• Unusual day follows below opposite to 1 across
• Rare find unfortunately can't be seen
• It's invisible below lightly cooked bit of dinner
• Type of radiation
• Fan drier (anag) - type of radiation
• (Of radiation) with a longer wavelength than light
• Having longer than visible wavelength
• With a frequency between the red end of the visible spectrum and microwaves