Add HiddenLight plugin please.
Link: http://dev.bukkit.org/bukkit-plugins/hiddenlight/
HiddenLight is a useful and nifty plugin that will allow the creation of Hidden Light Sources in your world, without needing to use torches, glowstone or blocks that emit light. This is an extremely useful tool for mapmakers who require their map to be well lit at certain areas, or server owners who simply want to light up their spawn.