Which is better for flowering? HPS or MH? 420 Guide for Beginners

Which grow light is best — HPS grow lights or MH grow lights — is perhaps the most common questions among those new to indoor gardening or HID grow lights. Ironically, most HID grow light enthusiasts recommend using both MH and HPS grow lights. MH grow lights (metal halide) are suited best for vegetative growth and HPS grow lights are superior for flowering. While either type can be used for the full growing cycle, when combined, using an MH grow light for vegetative growth and flowering under an HPS grow light is the most recommended HID grow light setup because utilizing the strengths of both types at the right times produces the best results. If you’re forced to make a choice between the two types, your decision should be based mostly on the type of plants you’re planning to work with.

What do MH and HPS mean?

MH stands for Metal Halide. These are grow lights that give off a blue color and are designed to project a similar light to spring in order to aid the photosynthesis of your plants. For this reason, MH lights are specifically designed to be used during the vegetative stage of your plant’s growth cycle.

HPS stands for High Pressure Sodium. In comparison to the MH grow lights these give off a red/orange light and are designed to replicate the autumn or fall sunshine in order to encourage the growth of your flowers. There are also HPS grow lights available that can also give off light on the blue spectrum, so can also help with the vegetative stage of growth.

Metal Halide Vs. HPS: So Which Bulb Should I Get?

The best answer is both.

You’ll get the best results if you run both bulbs all the time, but this is quite expensive, so we recommend using MH bulbs during seeding and/or vegging and using HPS bulbs during flowering.

If you only use one bulb throughout the grow cycle, you’re better off going with HPS. It will result in spindly plants (due to lack of blue light, which helps plants grow strong), but using MH during blooming is worse. It has a fairly large negative impact on yields, because flowering plants really need that red light.

What’s the difference between Metal Halide and High Pressure Sodium?

MH lights are generally used in the vegetative stage of growth (when young plants are growing just stems and leaves), while HPS grow lights are considered optimal for use during the flowering stage when cannabis plants are producing buds.

Either MH or HPS lights can be used for the entire grow and will get good results, but modern ballasts often allow a grower to interchange MH and HPS bulbs, so many growers choose to use what’s been proven to get the best results and grow with both types of bulbs. If you want to use MH and HPS bulbs with the same ballast, it’s important you look for this feature to make sure you don’t accidentally put the wrong bulb in the wrong hps ballast.