- Sephardim generally make the Blessing on Ner Shabbat PRIOR to lighting. This is in keeping with the principle of reciting the Blessing PRIOR to the performance of the Mitzva
- Ashkenazim - possibly based upon a mis-read of Halachot G'dolot - Bless after the lighting. Then comes the practice [Minhag] of covering one's face whilst reciting the Brachah. Why?
The common reason given is that since the order of blessing & Mitzva have been reversed, one needs to avoid benefiting from the lighting until the Blessing has been completed. Actually this reason is quite rational
While working in a nursing home I heard different explanation. The way I heard it was:
You see during Roman times people worshipped FIRE so in order to NOT be perceived as blessing the fire Jews covered their faces.
The way I interpret this is that the Parthians were fire-worshippers and this was indeed a halachic problem for those blessing the fire AFTER the lighting! So it makes sense to cover one's face while blessing on the Shabbat Candle not because of going out of order per se, but since the light/fire is there while the blessing is recited it behooves us NOT to bless the fire itself lest it be construed as fire-worship