Crossword Clue:

the period of this light

AnswerCrossword Clue
KRYPTONISOTOPEThe length of a meter is based precisely on the amount of light emitted from this
DAYTIMEPeriod of light
DAYLight period
SEMYou might get credit for this period of work: Abbr.
ANOEnero is first in this period
ENGLISHTEXTBOOKIn this, a "." is a "period"
TRIASSICArizona's Petrified Forest dates from this period