A white Ping-Pong ball has a special property: Light scatters off the interior surface of the ball with equal intensity regardless of viewing direction. Surfaces exhibiting this property are called Lambertian surfaces.

Some light is transmitted through the ball wall because it is thin and not perfectly opaque. Therefore, the external appearance of the ball is the same color as the light illuminating the interior. If we put the glowing point LED source inside the Ping-Pong ball, the ball will appear equally bright from all directions. Make three holes in the ball wall by using the hot tip of a soldering iron. The holes should be just big enough for the LEDs to sit in without falling into the ball. In order to obtain a decent white color, a fine adjustment of the current through each LED is required. I used a simple circuit shown in Fig. 1(b) with a 4.5-V voltage source (three AAA batteries) and 100- variable resistors. The value of the fixed resistors should be chosen so that the current through each LED does not exceed the forward current as specified by the manufacturer (normally 20–30 mA) at the lowest setting of the variable resistor. The values of fixed resistors that are indicated in the figure refer to my choice of LEDs. The power rating of all the resistors is 0.25W. I used a plastic film container as a stand for the ball and fixed all the elements on a black foam board with a glue gun [see Fig. 1(a)]. Make a slit at the top of the light ball [see inset in Fig. 1(a) photo] again by using the hot tip of a soldering iron. This slit will be useful for experiments, which I will address later.

Figure 1.