Is there a specific type of light source that outperforms others for indoor urban gardens?
This could be a combination of power usage and its effect on growing plants (i.e. spectrum it produces).
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Both LED and flourescents can produce 'ideal' lighting conditions for plants. LED Lights are the most efficient measured in lumens per watt, and also in terms of material waste, since they last longer and are smaller. Their biggest current disadvantage is that they are significantly more expensive upfront. Depending on the model and how you figure the costs, LEDs can still be cheaper in the long run due to energy efficiency and lifetime.
source: National Geographic
I did find some hydroponics and lighting supply shops that told me there are spectrums that help different kinds of vegitation grow.
A cheap Home Depot solution from windowFarms.org: Compact Fluorescent (CFL) light bulbs in Daylight Spectrum (5500+ Kelvin color temperature) 100 watt incandescent equivalent or 27 actual watts