Table II. Effect of intensity of illuminating light on the proportion of sperm across fields that undergo spontaneous fluctuations.

	ND2 + 4	ND4	ND2	Direct
Number of sperm	48	51	71	56
Total number	448	469	511	511
Proportion (%)	10.71	10.87	13.89	10.96

Cells were illuminated directly, and the proportion of cells undergoing spontaneous fluctuations in a 12.5-s recording period was measured. Subsequently, neutral density (ND) filters of increasing strength (ND2, ND4, and ND2 + 4) were introduced into light path and recording was repeated as before.