Smaller BT-37 glass jacket (400 watt size) with 1000 watt arc tube. Horizontal operation only. Glass envelope clear. Pin must come to rest at the 9:00 position. Rated best of all standard Metal Halide Lamps.The High Intensity Discharge metal halide grow lamps from Venture originally were and still are used for street and warehouse lighting. They have been selected for use in horticulture applications because of the light spectrum they emit. They are limited to the 4k (four thousand Kelvin) color temperature range, which is generally considered to be a good all-around vegetation spectrum. While you could use them for bloom growth, it is suggested that you burn a High Pressure Sodium or a Sunmaster Warm lamp along with it to increase the red, yellow and orange spectrum. It is good to note that of all the colors in the spectrum, plants need a larger percentage of the blue spectrum to be healthy. This is the color that drives photosynthesis and translocates sugars. The red, orange and yellow colors of the electromagnetic light spectrum are hormonal tripping colors. This is to say that when the plants have these electromagnetic wavelengths pass thru the leaves; bloom hormones are produced in the anticipation of the coming fall and winter seasons. Note: Lamps labeled HOR (horizontal) and BU (base up) are position oriented and will give you the highest light output available for their wattage. They are designed to burn in their designated positions only. Lamps labeled U (universal) may be burned in any position. However, they will be less bright than position oriented lamps with the same wattage.