The NFRC Directory should start listing SHGC starting in January 1995. This affects daylighting and the ability to see objects and views outside. The human eye can adjust to wide variations in visible light, so it compensates to some degree for low VLT numbers. Clear glass has a value of 90 percent. For most residential applications, VLT should be between 40 and 70 percent.
Reflectance describes how much visible light is reflected back toward the source.
The numbers are listed for inside, outside or both. A few people find interior reflectance a problem, too. Be sure to distinguish between visible reflectance and solar reflectance, which may also be listed in the product literature. When LSGR equals 1.0 the same fraction of light and heat gain pass through the window. For climates where cooling is more important, ratios above 1.0 are better, because light transmittance is higher than heat gain.