Related Clues:

• Like some rays outside the visible spectrum
• Between visible and microwave
• Visible through night-vision goggles, say
• Such photography has popular female artist looking embarrassed
• Kind of bulb in a heat lamp
• Find out about unusual type of radiation
• German woman nearly gets into debt - that doesn't normally come to light
• Drunk friend covers artist in radiation
• Stylish brother a cardinal? I can't see it
• Remarkably rare find that is out of our range
• Knowledge largely hard to find by day? None of us can see it