Answer:
3.5mm I guess
Explanation:
More professional people will give you the correct answer... this is just a try
The visible light has wavelength in therange 400 - 700 nano-meters. The wavelengths longer than visible light are: 1-Infrared waves (used in ringtone/mobile waves)2-microwaves -used to heat and cook food. 3- Radiowaves - used in communication