Prism Lab is a light and mirrors puzzle. Emitters shine coloured beams across a small grid, and every target wants exactly its own colour. You have a tray of mirrors and splitters. Tap an empty tile to place the selected piece, tap it again to turn it the other way, and tap a third time to put it back in the tray. Mirrors are two-sided. Splitters let a beam pass straight through and also reflect a copy.
Beams add up where they meet at a target: red and blue make magenta, red and green make yellow, and white light is red, green and blue together. The dots under each target show its recipe and fill as colours arrive, and a target getting an unwanted colour shows a dashed ring. Walls and emitters block light. In later tiers, filters keep only their own colours, so white passing through a yellow filter comes out yellow.
Par is the fewest pieces that light every target. Matching it earns three stars and one piece over earns two. Undo takes back a step. The hint makes the next move towards the optimal solution for you and caps the level at two stars. Sixty levels run from First Light to Master Lab, with a daily level.
Worked example
A red target and a magenta target share the board with a red and a blue emitter. Put a splitter in the red beam. The straight part carries on to the red target, while the reflected copy can be steered with a mirror to the magenta target, which already receives blue. Red and blue together make magenta, and both targets glow.
Strategy tips
Read the recipes. A mixed target needs two beams, so plan where each one comes from.
Trace backwards. Start from a target and ask which lit tiles could send light into it.
Watch the crossings. One splitter hit by two colours can feed two targets at once.