Photographic paper reacts to light to produce the image taken by a camera and stored on film. Darkrooms used red lighting to allow photographers to control light carefully, so that light-sensitive photographic paper would not become overexposed and ruin the pictures during the developing process.
Trade barriers come in many forms. Quota is one. This is when a country sets a limit to the imported products. This is done for a number of reasons. One is because the government of the importing country wants to protect its domestic manufacturers. Other barriers or limitations are added costs such as tariffs, duties, and taxes.