Lemongrass (Cymbopogon flexuosus) has a light, fresh, citrus aroma with earthy undertones. Refreshing, rejuvenating, stimulating, and balancing, it inspires and improves mental clarity.
The difference is that ultrasonic diffusers use water and essential oils to create a cool mist of water/oils that releases in to the air. They double as a humidifier, so they are beneficial in winter, but they don't put out as strong of a concentration of essential oils since they also use water.