An apparatus for determining a power frequency of a light source, the apparatus comprising: a photo-sensor coupled to generate an electrical signal responsive to light incident thereon; a modulator circuit coupled to the photo-sensor to generate a modulated signal based on the electrical signal that toggles at a rate substantially proportional to the power frequency of the light source; and a logic unit coupled to the modulator circuit to determine a toggling frequency of the modulated signal and to generate a frequency select signal indicating the power frequency of the light source; wherein the modulator circuit comprises: a comparator including first and second comparator inputs and a comparator output, the first comparator input coupled to the photo-sensor and the second comparator input coupled to receive a reference signal; and a charging source configured to selectively charge the first comparator input based on feedback from the comparator output, wherein, in response to the first comparator input being less than the second comparator input, the feedback from the comparator output causes the charging source to charge the first comparator input; and wherein, in response to the first comparator input being greater than the second comparator input, the feedback from the comparator output causes the charging source to stop charging the first comparator input. a photo-sensor coupled to generate an electrical signal responsive to light incident thereon; a modulator circuit coupled to the photo-sensor to generate a modulated signal based on the electrical signal that toggles at a rate substantially proportional to the power frequency of the light source; and a logic unit coupled to the modulator circuit to determine a toggling frequency of the modulated signal and to generate a frequency select signal indicating the power frequency of the light source; wherein the modulator circuit comprises: a comparator including first and second comparator inputs and a comparator output, the first comparator input coupled to the photo-sensor and the second comparator input coupled to receive a reference signal; and a charging source configured to selectively charge the first comparator input based on feedback from the comparator output, wherein, in response to the first comparator input being less than the second comparator input, the feedback from the comparator output causes the charging source to charge the first comparator input; and wherein, in response to the first comparator input being greater than the second comparator input, the feedback from the comparator output causes the charging source to stop charging the first comparator input. a comparator including first and second comparator inputs and a comparator output, the first comparator input coupled to the photo-sensor and the second comparator input coupled to receive a reference signal; and a charging source configured to selectively charge the first comparator input based on feedback from the comparator output, wherein, in response to the first comparator input being less than the second comparator input, the feedback from the comparator output causes the charging source to charge the first comparator input; and wherein, in response to the first comparator input being greater than the second comparator input, the feedback from the comparator output causes the charging source to stop charging the first comparator input.