A box (1) with lid (6) is mounted on the upper binding of a book and contains a luminous diode or bulb (2) and batteries (3). A flexible plastic tongue (4) which is fixed to the book cover has a slot (5) which allows electrical contact to be made when the book is opened and prevents it when the book is closed. The diode or bulb emits back light thus enabling fluorescent or phosphorescent illustrations to become visible in the dark
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