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When considering light-blocking capabilities, you should first think of curtains for a bedroom or other space where you need to block out light. The blackout fabric can prevent you from waking up by sunlight or reduce energy costs by cutting the amount of sunlight enters the room.
Opacity is the ability of a fabric to block out light and provides coverage from light. It is determined by the light blocking properties of window covering textiles against light passing through them by spectrophotometrical method. The light-blocking properties can be measured on an instrument that supports measurement in transmission mode. The spectrophotometer measures light passing through samples placed behind it.
Good opacity features can help keep out the heat, sunlight, and UV rays to make the users feel comfortable as well as help reduce solar heat and protect from direct sunlight.
Opacity can also protect the materials inside from direct sunlight damage to finish/paint while in storage. Moreover, the blackout curtains can help to reduce outside noise from entering the room.
The testing procedures of light blocking testing, AATCC 203, are as below:
Block the external/reflectance port with a white standard to complete the sphere.
Set the machine to transmission measuring mode without any sample in the transmission holder.
Measure and record total transmission, using the CIE YD65-10 tristimulus value, which should result in a measurement of 100.
Operational check of total transmission with opaque light blocking.
Keep the white standard in place at the external/reflectance port to maintain the completed sphere.
Block the transmission port with an opaque, black standard, such as a metal plate.
Measure and record total transmission. The CIE YD65-10 value of the measurement should be 0.
Record transmission through the specimen material.
Keep the white standard in place to maintain the completed sphere.
Place the specimen to be measured in the transmission holder clamp.
Measure and record the light transmission using the CIE YD65-10 tristimulus value.