Changing lights

I have a plant, about 4 months old growing under some flouresent lights... kinda ghetto, but the plant is about 3 feet tall and has about 1/8 on it and is covered in crystals and going good.. Slow, but good. If I put a 400 Watt Hps over it this late into flowering, what will happen?? Probably a stupid question but...... Thanks for helping

it will help it loads and speed the flowering period slightly

Not to mention increase yield.

How close is it to maturity? Checked the tricomes?