“Dual Arc” HID lights combine a high pressure sodium and a metal halide in a single HID bulb.
Intensity of Dual Arc vs. LED Grow Lights
Dual arc bulbs are intermediate in intensity between their HPS and MH components. They are certainly brighter than 1W LEDs but 5W and some lensed 3W LED grow lights have higher intensity.
Spectrum of Dual Arc vs. LED Grow Lights
Combining the spectrum of MH and HPS yields a bulb with the blue and red plants want, but also with a double-dose of the green and yellow light that plants can’t use efficiently. The MH portion of the bulb does add some UV to the mix to enhance the quality of plants.
Because LEDs allow complete tuning of the spectrum, well-designed LED grow lights can provide just the colors of light that plants want without any of the waste.
Lifespan of Dual Arc vs. LED Grow Lights
Dual arc bulbs only last as long as the metal halide portion of the light, so they have a relatively short lifespan for an HID bulb. They typically need to be replaced every 6 months when used to grow plants. Well-cooled LED grow lights offer lifespans 10-20 times as long.
Efficiency of Dual Arc vs. LED Grow Lights
Dual arc bulbs are intermediate in efficiency between MH and HPS lights, but still nowhere near as efficient as LED grow lights.