High Pressure Sodium lamps are more efficient than Metal Halide, producing the highest number of lumens per watt - about 10-15% more than a Metal Halide bulb. HPS emits an orange/yellow color that is similar to the sun's spectrum in the mid day. This type of light promotes flowering and budding. However, the lack of blue spectrum light can sometimes make a plant stretch during the vegetative growth stage. Enhanced performance HPS lamps provide some of the blue light missing from standard HPS Lamps.