I’m afraid I don’t quite understand the question, so I’ll try interpreting it a few different ways:
– The lightest planet in the solar system is Mercury at a mere 3.30 000 000 000 000 000 000 tonnes!
– The smallest flowering plant in the world in watermeal, coming in at around 0.1 g
– The plant the emits the most light is probably Neonothopanus gardneri or flor de coco – a bioluminescent mushroom from Brazil
– The planet that emits the most light is probably Jupiter because it produces a lot of infrared radiation