hello im very new to growing and at the beginning of my first grow. As I said im growing in a 3x3 tent with the spider farmer se 3000. Ive germinated and planted 4 seeds in coco. ive had the light set around 45 percent just because i heard someone in a video say thats what they did for their seedlings but that wasnt even using the same light as mine. My questions are what setting brightness should the light be at and when. Ive also had the light set at 2 ft away. Are these things set in stone? Do i ned to learn about par? Please Help
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Welcome to the community. You need to visit with the expert light man. I will tag him for you. @dbrn32 this grower needs your help. 
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welcome to the community.
Welcome to the community I’m sure spider farmer has recommendations for that light I would check the website or manual
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Download the photone app, and then select the type of light it emits and it will tell you your DLI. That will let you know whether to increase the % or lower the light, or both.
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Ensure the fresh air is changed ~every minute so the plant has a steady supply of CO2. Plants take in – or ‘fix’ – carbon dioxide from the atmosphere during photosynthesis.
Take room and leaf temp, a humidity reading, and plug those numbers into a VPD calculator (link below) to understand where you are as far a transpiration is concerned.
Maintaining the vapor pressure differential (VPD) between the room and leaf for the plant’s stage of growth will allow it to open and close the stomata so it can transpire. Transpiration is the pump that allows the CO2-O2 gas exchange and moves nutrients and water throughout the plant. This pump even allows the roots to absorb nutrients. Exceeding VPD tolerance can cause the pump to run too fast or shut it off. Either case can result in disease and/or mineral deficiencies.
If your canopy leaf temp is higher that your room temp your lights are too low. The room temp is far less of a concern than leaf temp. After all, the goal is growing a plant not heating a room. If your leaf temp exceeds ~85* your room is too warm. Measure it with a laser pointer in several places around the canopy. Cool the canopy by raising lights, moving fresh air in and expelling hot air, air conditioning, defoliating to allow air circulation, or by using a combination of these.
After any leaf temp issues are resolved, then ensure your lights are set to proper DLI to optimize photosynthesis. High intensity lights can be controlled so photosynthesis can create food and use the provided water and nutrients. Balance photosynthesis by providing the plant’s light requirements for the growth stage it’s in. The Photone app is a cheap and easy way to measure light with your phone. It will toggle between PPFD and DLI.
After adjusting lights recheck VPD (leaf, room, humidity). Find a balance between VPD (transpiration) and DLI (photosynthesis) by controlling the environment.
As the plant grows, when you transplant, make changes, etc., adjust the environment balance based on the VPD and DLI requirements for the stage of growth the plant is in. This is a frequent task based on growth rate. Taking light, temps, and humidity readings and making adjustments are far more frequent than feeding or watering because the plant is always growing.
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Not super familiar with this light, but 2’ at about half power seems pretty good to me. All you need to do really is keep an eye on your plants. If they stretch too much turn it up some.
Ok so how much stretch is too much? Also, at some point dont you turn up the lights? Do you turn them all the way up when you switch to flower?
If they start looking tall enough to fall over is too much. I built my light to run about proper ppfd average at 2/3 power in veg. Once I flip to 12/12 I start increasing a little every few days, with target to be at full power 15-20 days after flip. This is about best results I can get.
