Electricity use and resource efficiency is rarely under the direct control of the couple renting the venue.  Using less energy has less to do with new technologies and more to do with a creative response to limitations—even old, incandescent lights simply can be switched off, perhaps in favor of romantic candlelight. If your venue does not offer efficient lighting and heating, consider asking your venue manager for ways to adjust the thermostat and turn off any lights that are not necessary for use at the time of your reception.