In practicality, Light intensity doesn't have a direct effect on germination, but HEAT does! All light, especially light from fluorescent tubes and even more so from incandescent, will warm the soil. Yes, there is definitely a difference in soil temperature depending on how much light reaches the soil. Remember your physics class: the farther away from a light source, the less light intensity(and indirectly, less heat). The inverse square law applies here: light intensity is reduced by the square of the distance. That's a big difference.
So the soil near the light is warmer, causing faster germination. Unwittingly, you performed a sixth grade experiment: The Effects of Light and Temperature on Radish Seed Germination.
