impinges upon the mirror and the other mirror are oriented relative to the source such that light from the source traveling along the first optical path travels in a direction opposite to light traveling from the source along the second optical path a collector having a discharge extreme ultra violet light source is also described application_number US 5404005 A description in order to reduce the cost of an euv condenser more efficient collectors should be designed by designing collectors that are capable of directing more photon energy from the light source into the illumination system the amount of light energy needed from the source can be reduced which in turn should lower the cost of the condenser as a whole because less expensive euv sources can be used two types of euv light sources that are presently in common use are laser produced plasma lpp sources and discharge sources fig3 though 6 show designs for efficient euv collectors that include an lpp source and fig7 through 9 show designs for efficient euv collectors that include a discharge source a discussion of these designs immediately follows fig3 though 6 show designs for efficient euv collectors that include an lpp source according to the designs of fig3 though 6 efficiency is improved over prior art lpp sourced euv collectors through then collection of light over approximately a sphere that surrounds the lpp source prior art lpp sourced euv collectors such as the source 203 of koch et al shown in fig2 are believed to only collect light over approximately no more than a hemisphere resulting in less collected photon energy than the designs observed in fig3 though 6 another feature of the collector designs.