# illumination

## 16 - Light placed above the center of circular area

**Problem 16**

A light is to be placed above the center of a circular area of radius a. What height gives the best illumination on a circular walk surrounding the area? (When light from a point source strikes a surface obliquely, the intensity of illumination is

$I = \dfrac{k\sin \theta}{d^2}$

where $\theta$ is the angle of incidence and $d$ the distance from the source.)

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## 72 - 74 Light intensity of illumination and theory of attraction

**Problem 72**

A light is to be placed above the center of a circular area of radius a. What height gives the best illumination on a circular walk surrounding the area? (When light from a point source strikes a surface obliquely, the intensity of illumination is

$I = \dfrac{k \sin \theta}{d^2}$

where θ is the angle of incidence and d the distance from the source.)