As per the title, how energy efficient is aquarium lighting?

I ask as the lights on my new tank are so bright that they illuminate the room they are in quite well.

Fairly, certainly running T5s on my 180 litres doesn't cost much leccy wise. The bill didn't go up much when I started to keep aquariums when compared to bills the year before.

LEDs are probably the way to go, last much much longer and need far less power. Until some of the prices come down though, most keepers will stick to tubes I think.

Just multiply the wattage of the bulbs by the number of hours per day they re on and you'll see how much they use.
For example 2 x 54 watts on for 8 hours a day is (2x54)x8=684 watts. Over a week that's 6 KwH at whatever your electricity price per unit is. Average is about 15p a unit so in this case the cost is 90p a week.