Metal Halide (MH), High Pressure Sodium (HPS) and Mercury Vapor (MV) lights are different types of H.I.D. (High Intensity Discharge) lighting. Metal Halide and High Pressure Sodium lamps work great for garden lighting because of their high light output per watt, and the color (spectral) distribution of their light. Plants need blue/ green color spectrum for vegetative growth and red/ orange spectrum for budding and flowering. Mercury Vapor lamps are useless for plant growth due to their poor spectral distribution of light, they have almost no blue/ green and no red/ orange. While MV lights are inexpensive to use in your indoor garden, don't bother, they are not worth it.

Here is a description of the different types of HID grow lights

High-Pressure Sodium/ Son Agro lamps
There are two type of HPS bulbs, standard HPS and enhanced spectrum HPS such Son Agro and Hortilux. If you are using lamps to supplement natural sunlight, these are the best lamps to use. Son agro and Hortilux bulbs may be used in standard HPS ballasts, ie; you can use a 430 watt Son agro bulb in a 400 watt hps ballast.

Standard High-Pressure Sodium (HPS) lamps are very high in red/orange color spectrum and are used to promote budding and flowering in plants. Purchase HPS bulbs here

Son Agro and Hortilux bulbs emit more blue spectrum than standard High-Pressure Sodium lamps, thereby reducing inter-nodular elongation of plants. Son agro bulbs offer the added benefit of increased lumen output. These lamps work well in conjunction with sunlight, or as the sole source of light. Son Agro and Hortilux bulbs are most often the choice of proffesional growers. Purchase Son Agro and Hortilux bulbs here

Metal Halide lighting systems
There are several varieties of Metal Halide bulbs that will all run off of a standard metal halide ballast. These are: standard MH bulbs, MS bulbs, and Daylight bulbs. Here are the differences:

Metal Halide -These bulbs are high in blue green spectrum (which is needed to promote vegetative growth), with some red/ orange spectrum (needed to promote flowering). These lights lamps are used primarily ro promote stocky, lush vegetative growth. Purchase MH bulbs here

Metal Halide/ MS - These lamps emphasize the blue/ green spectrum to promote vegetative growth. If you have little or no sunlight available these are the systems to use. MS lamps contain a 30% boost over standard Metal Halide lamps in the red/orange spectrum for flowering, and more lumens per watt (light output) than standard Metal Halide lamps. These lights are used for vegetative growth and can be used with flowering plants as well. Purchase MS bulbs here

Daylight bulbs- are very high in blue spectrum (4or 5 k output) and also high in red/yellow. This makes Daylight bulbs an excellent light source for propagation and for supplementing HPS lamps. Purchase Daylight bulbs here

You MUST make sure to use the correct wattage of MH lamp in your MH ballast, ie: a 400 watt bulb for a 400 watt ballast.

Conversion Bulbs
Conversion bulbs allow you to change the type of bulb that you are using in your ballast. There are two types of conversion bulbs:
Sodium bulbs which run on Halide ballasts - These are available for most MH systems.
Halide bulbs which run on Sodium ballasts - These are available for 400 or 1000 watt systems only. Purchase conversion bulbs here

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