Normal sudoku rules apply. Digits on a grey thermo increase from the bulb to the tip. Any set of three sequential cells along a line must contain a digit that is 1 mod 3 (147), and a digit that is 2 mod 3 (258). and a digit that is 0 mod 3 (369). Vertical columns on a keypad are a good reference. All lines in this puzzle conform to both rulesets. In the case where thermos share a bulb the entire line is considered for the modular logic.