A UV lamp or black light lamp is optional, but recommended for the full RUNED experience with glowing ink.
These are available for between €5 and €20 on Amazon and other retailers.
However, UV light is also present in natural sunlight.
Theoretically, you can solve the puzzles without UV light, but then you won't get the full WOW factor with the glowing inks.
For a limited time, a RUNED UV lamp is available for free as a goodie with the book. However, due to strict electrical appliance regulations, it may not be included depending on your country or specific retailer. It is best to just buy the book and see if a lamp is included as a bonus item. The price is the same with or without the lamp, as it is a free bonus item.