IPA: //aɪsəˈfoʊtəl//
KK: /aɪsəˈfoʊtəl/
Relating to lines or areas that have the same level of light or brightness.
The isophotal map showed the distribution of light across the landscape.
Isophotal is formed from "iso-" (meaning equal) and "photal" (derived from the Greek "phōs", meaning light). The word refers to areas that have equal light intensity.
Think of 'equal' ('iso-') light ('phōs') when remembering that isophotal refers to regions with equal light intensity.