What is "VLT" and why is it important in a commercial skylight?

VLT, or Visible Light Transmittance, is the measure of light that is transmitted through a skylight or window. A high VLT is important as it indicates how much light is transmitted from the outside of the building to the inside through the skylight. Since the value of daylighting is in delivering the most usable light, you always want to achieve the highest VLT while meeting local code requirements for thermal transmittance.