This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: X-RAYS, Subject name: Radiology
SAFE LIGHT used in conventional radiography emits which colour of light? 
Select and explain. 
A. Blue, B. Green, C. Red, D. Yellow
C: Red
Answer: C: Red 
Explanation: Darkrooms used red lighting to allow radiographers to control light carefully, so that light-sensitive photographic film would not become overexposed and ruin the image quality during the developing process.