I have been told T5 will encourage root growth.

LED is working for me though. I currently germinate in a 90w LED under a humidity dome.

I veg in LED and 6500k T12s and UVB.

I have not directly compared the two techniques. You could consider using both types in one space. You can use a $10 lumen reader from a nursery or hydro store, and then adjust the light distance until it reads the desired lumens.

I like to be precise though; you could just wing it since both work.

EDIT:
Here are pics of plants germinated from seed under T5s. I'm babysitting so they are in my LEDs, but they have only been in them about a day in this photo.

Germinated In T5 Lights

Here are my sprouts in the 90w LED:
Germinating in LED

Clearly mine are much younger at this stage.