500 lumens (bad choice of measurement, by the way... probably better to use watts and light type, or at least lumens + light type + light color) is almost nothing. If you want something that high up that's to encourage flowering, it should probably be a high pressure sodium, at least 250W. A 250W HPS will put out *20-30 thousand* lumens.

I have used T5 grow lights for indoor gardening.T5 grow lights are an excellent option for indoor garden when considering the low cost, low energy, and longevity of the system.

Here is a link that might be useful: led flood lamps

You don't use lumens at all, lumens is human light only. You use photon flux density at a given distance to measure light output.