Candelae

The form of the plural, too, calls for consideration. The Latin is candelae and the Italian candele, but candelas has already been used officially in Belgium and will probably be used in France. It will almost certainly be preferred in this country and in America, where candelae would be deemed pedantic.

The luminous intensity of this source of light has been defined as 60 candelae per cm² in the direction of the normal to the surface.[…]Nowadays however, candelae per m² are often used as the unit for luminance.

Fig. 1 / The visual recovery in the dark after pre-adaptation to 15.5×10³ photopic candelae /m², as studied in the Goldmann and Weekers’ adaptometer.

Candelae are calculated on the basis of a perfect or “ideal black-body” irradiation equal to solidifying platinum at a temperature of 2042 K. The luminous intensity of such a system is 60 candelae/sq cm when measured[…]