How much light your plants need will vary based on each phase of the grow cycle. Seedlings can’t take a lot of light, but once a plant is in veg, it needs just about all the light it can get. This allows plants to grow vigorously to their full potential. The same goes for flowering.
A lux meter is a relatively simple device with which you can measure the amount of light (lux=lumens/m²) in your grow room. What makes a lux meter attractive compared to a PAR meter or quantum light meters used by professionals is that it is much cheaper.
For healthy growth and good yields, almost nothing is more important than providing your cannabis plants with plenty of light. With an affordable lux meter, you can measure and optimise the amount of light in your grow-op to increase your yields.