4. (3 points) On the clock tower of a railway station, there is an electronic clock. On the boundary of the circular clock face, there is a small colored light at each minute mark. At 9:35:20 PM, there are $\qquad$ small colored lights within the acute angle formed by the minute and hour hands.
【Analysis】First, find the angle between the hour hand and the minute hand at 9:35:20 PM; then, according to the clock face being divided into 60 small segments, with each large segment corresponding to an angle of $30^{\circ}$ and each small segment corresponding to an angle of $6^{\circ}$, we can find the minute marks between the hour hand and the minute hand at 9:35:20 PM, and thus determine the number of small lights inside the angle between the hour hand and the minute hand at 9:35:20 PM.
【Solution】At 9:35:20 PM, the angle between the hour hand and the minute hand is:
$$
\begin{array}{l}
9 \times 30^{\circ}+35 \times 0.5^{\circ}+20 \times 0.5^{\circ} \div 60-\left(7 \times 30^{\circ}+20 \times 6^{\circ} \div 60\right) \\
=270^{\circ}+17.5^{\circ}+10^{\circ} \div 60-210^{\circ}-2^{\circ} \\
=\left(75 \frac{2}{3}\right)^{\circ} \\
\left(75 \frac{2}{3}\right)^{\circ} \div 6 \approx 12 \text { (units). }
\end{array}
$$

Therefore, there are 12 small lights inside the acute angle between the minute hand and the hour hand.
The answer is: 12.