The visible transmittance is an optical property that indicates the amount of visible light transmitted. It is the fraction of visible radiation transmitted by a glazing system between the limits of 380 and 770 nanometers (0.38 - 0.77 micrometers). It is weighted according to the photopic response of the human eye (V-lamdba curve) and is expressed as a number between 0 and 1, most values are between 0.3 and 0.8. Also known as visible transmittance (VT) or visible light transmittance. The higher the VT, the more light is transmitted. A high Tvis is desirable to maximize daylight. A balance between glazing area and Tvis will minimize glare and maximize useful daylight.