Detect-o spy Lamp

The Detect-o Spy Lamp is a special light used to reveal messages written in invisible ink. Fern used one in "Fern & Persimmony Glitchet" 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.