Emission pattern of HPS Grow light

In a way similar to the CFL, light is emitted from a glass tube and goes in every direction-- almost 360-degree light emission. Only about 30% of the light actually goes in the direction we want. So we need a reflector to collect all that light and redirect to where we want.

We said earlier that there is a precise mathematical relationship between size and location of the light source and the shape of the reflector. In a precision incandescent or halogen reflector-as in a par lamp, the filament is very much smaller than the reflector. However, in the HPS unit used as grow-light the reflector is not large enough to have mathematical precision. It would have to be much greater size and weight—and far more expensive--- maybe 36 inches in diameter--- to perform well as an incandescent par lamp.

All this means that 100% of HPS grow-lights (all of them have built-in reflectors) do not focus the light very well. They do have good light uniformity across the grow bed. Unlike most LED grow light they do not have “hot spots ( (i.e. excessive light) in the center and poor light around the sides. But they achieve that uniformity by wasting a very significant amount of light sent off to the sides.

HPS have many serious disadvantages and hidden costs but and user do all kind so things to compensate for the disadvantages because of the low price. However new development, such as high-performance low-cost MultiBEAM technology, will make it more and more undesirable to use HPS.