New using light other then sun

So i started off my first indoor grow and had a few questions on lighting
1.when do you know when to turn the wattage up on your fixtures
2.my light is the roi e420 the dimmer knob goes (ext , off 25 50 75 100) ive searched everywhere and cant seem to find out what the ext function is. it seems to be the brightest mode visually tho

2: my guess it means you disconnect the dimmer entirely and make it so it can take an external dimming input from a controller

Rocket Soul said:

2: my guess it means you disconnect the dimmer entirely and make it so it can take an external dimming input from a controller

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That would make sense. Thank you

You should talk to the manufacturer. The emitted light intensity is measured in so called PPFD. Brands should present PPFD maps with their lamps. A PPFD map will show what light intensity the lamp emits at various heights. For veg, for instance, you'd want PPFD of around 200-400 but for late flowering, close to 1000. The PPFD maps need to show at what distances you achieve this. It's impossible for us to speculate what light intensity a certain grow light emits at a specific height. This is the grow light brand's job to inform you of.