You may be surprised by the efficiency of different light sources, ranked by Lm/W look at these sources:
- 200 Low pressure sodium
- 150 Metal Halide
- 100 28w t5 florescent tube
- 93 36W t8 florescent tube
- 60 cfl light
- 26-70 LED (Very directional)
- 24 quartz halogen
- 15 standard incandescent
I have actually seen 35 watt metal halide lamps. They make very good outdoor lighting for constant on/long term on situations.