Lower leaves turning yellow and dying

I have 4 plants in 2 weeks veg stage under a 150watt cfl bulb and i need to know if i need to cover the stems with more soil because they are long and if i cut the bottom leaves off will it harm it.
 
Hi, I'm new to growing. I didn't have enough light since beginning so I guess the height and huge gaps between branches is consequence of that. But why did the bottom leaves (three fingered) stopped growing and started to die slowly? Those higher leaves seem perfectly fine and healthy. Thank you.
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Help please full noob here so plant is generally looking good but few leaves turned yellow at bottom and fell. Off I'm. Not horibbly concerned as the plant looks great otherwise but some suggestions would be appreciated

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