Los músicos de una sinfónica siempre ""calientan"" sus instrumentos de viento soplándolos antes de un concierto. ¿Para qué sirve esto?

The illuminance of a surface varies inversely with the square of its distance from the light source. if the illuminance of a surface is 120 lumens per square meter when its distance from a certain light source is 6 meters, by how many meters should the distance of the surface from the source be increased to reduce its illuminance to 30 lumens per square meter?