Seeds differ in their requirements -- some need light, some darkness; some need cool soil temps other warm temps. You won't be successful if you don't give the seeds what they require.

A lot of your question hinges on whether you use the lights to generate the warmth needed to heat the seeds or whether the warmth is coming from elsewhere (e.g. heat mat, placing on top of the fridge, etc). I don't use supplemental heat, so when I start under lights, the light is as close to the top of the seed tray as I can get it; this usually generates enough warmth for germination. Note I use florescent bulbs, not LEDs; I don't think LEDs would generate enough warmth.

For seeds that require darkness to germinate, covering with potting medium is usually sufficient, but there are a few where covering with something that blocks all light is beneficial (annual phlox comes to mind); something like black plastic will do.

It's not hard to germinate seeds and grow seedlings under lights, not at all; you just need to understand the basic principles of it.

I can't recommend this book highly enough: The New Seed-Starter's Handbook by Nancy Bubel | Goodreads

It taught me pretty much all I needed to know about seed starting, and even though it's old, the info in it is still sound.

You DO NOT NEED special "grow lights"; cheap fluro tubes work just fine, and a mix of warm and cool bulbs works best IME.

I just noticed you mentioned you use bottom heat. In that case, you don't need to put the lights as closely as I do, and if you're using fluros you shouldn't -- you might end up cooking them. A couple-few inches above the seed tray should probably be sufficient -- it's the light + the heat that's needed. After they germinate the light level is going to be more critical.

I have used flourescents, have largely moved on to tube style LED that are similar and use less power.

For 1 flat (22") I use a single 24" dual tube unit (19W total) that provides 1200 lumens. It does not need to be very close to the tray. I have both daylight and red/blue types which seem to work about the same, but the purple light is harder to look at. Each light 'tube' contains a single string of Leds about 1/2" apart. Perhaps you can use this to estimate how to apply the led light strings to your grow table.

If anyone wants to dig deeper into seed germination look here http://brahmsonline.kew.org/Content/Projects/msbp/resources/Training/13a-Germination-testing-procedures.pdf and the link from it to their " 13b " information sheet.

Happy New Year to all

I use 4' LED shop-style lights in my semi-heated basement (basement runs about 55 degrees). I switched over from the fluorescent tube lights a few years back. I put the lights on pulleys so I can raise and lower them according to the needs of each plant. I'm using those 48"x18"x72" wire (metro or NSF style) 5-shelf racks, and I put two sets of lights per shelf. I'm super lazy so I have the lights plugged into smart plugs so I can turn them on and off without going downstairs to the basement.