The sun’s rays can be magnified by a lens or magnifying mirror, so it is dangerous to leave glass objects, like magnifying mirrors, too close to windows, as they can concentrate the suns ray, causing nearby objects to set fire (curtains / clothing / paper or furniture). 

In fact, anything that can concentrate the sun’s rays, such as fish bowls or glasses of water, should be kept away from windows to reduce the risk of a fire breaking out. 

Safety advice 

• Keep magnifying mirrors out of direct sunlight. 
• Never put glass ornaments or paperweights on window sills. 
• Never place glass ornaments or paperweights in direct sunlight. 
• Make sure shaving or vanity mirrors are not left on window sills. 
• Be aware of objects in your home such as shaving or vanity mirrors and glass ornaments or paperweights that may be exposed to direct sunlight.