139:14 The entire time that the candles are fulfilling the mitzvah – which is about half an hour – it is prohibited for us to derive any benefit from their light. (Some are stringent to refrain from labor so long as they are still burning – Mishnah Brurah 672:8. OC 673:1 actually says that one may not “use” the light. One need not cover his eyes or risk tripping in the dark – Shaar HaTziyon 673:11.) The practice, therefore, is to place the “shamash” that was used for lighting the candles near the menorah. In that way, if one did some activity near the candles, he would be relying upon the light of the shamash. One must place the shamash slightly higher than the lights of the mitzvah in order to make it evident that it is not one of them.
139:15 Chanukah candles are lit in shul in order to publicize the miracle; the bracha is recited over them. They are placed by the south wall of the shul (arranged from east to west – Rema 671:7) and are lit between mincha and maariv. One does not fulfill his obligation in the mitzvah through the lights in shul; he must go home and light. (The one who lit in shul would not repeat the bracha of Shehechiyanu at home unless he is also lighting for others – MB 671:45.) A mourner should not light in shul on the first night of Chanukah because he would have to say the bracha of “Shehechiyanu” (that G-d has kept us alive until this occasion) and a mourner does not say Shehechiyanu in public. In his home, however, he may do so.