Magic Forums

When You do a ritual, and place candles on your altar, does several candles give a greater power to the spell?
I know that if you work in a coven, the energy becomes stronger.
And if you work as a solitary magician/witch the energy becomes weaker. I know that people will argue about that, but I know by experience.
Is it the same thing with candles?

Usually I use black candles, to attract and work with dark energies. I read somewhere that black candles drives away negative energies. Is that true? And by negative energies I mean jealousy, sickness, addiction,depression, hatred etc.
It seems inconsistent to me.

And thank you for any advice!