Rotate your plants each week.

The light from a fluorescent lamp is more intense at the center of the lamp than it is at the ends.

Clean your fluorescent bulbs each month.

Dust and dirt can dramatically decrease the amount of light emitted.

Replace fluorescent lamps when the ends darken.

That means the tube is old and the light output may be less than half of a new lamps.

Place your hand where the light hits the foliage.

If you feel any warmth, the light maybe too close.

If it feels good to you, it will feel good for your plants, pretty simple.