Detect-o spy Lamp

A detect-o spy Lamp is a special light used to reveal messages written in invisible ink. Fern used one to read Persimmony Glitchet's letters that were written in invisible ink. There is a chance that the lamp is Horrendously Horrible Happenings merchandise, as Fern said that Victor Bronte used one in Book 5: The Malevolent Mailbox.

The lamp probably emits ultraviolet light, which causes certain invisible inks to fluoresce.

Arthur

 * "Fern and Persimmony Glitchet"