Cooling fans can be added to these ports on some systems. These fans mount on the reflector and channel heat out of the room during the summer. In the winter, heat from the bulb can be vented down below the plants for additional warmth. Tempered glass shields, sometimes called lenses, are available for the better reflectors. Tempered glass keeps more of the damaging heat away from the plants, thus making it possible to lower the light source closer to the plants.
Lenses are also an important safety feature.
They block any moisture from ever reaching the bulb, which could cause the bulb to rupture. Hydrofarm's light systems have recently come out with a specular finish insert for their reflectors. Metal Halide Metal Halides produce an abundance of light in the blue spectrum. This color of light is excellent for green leafy growth and keeping plants compact. The average lifespan is about 10,000 cumulative hours.