A question regarding layl and ghasak al layl.

[Wakas]

It should be noted that our findings are in conflict with brother Joseph's article, quote:

Furthermore, it is clear from verses 91:1-4 that 'layl' (night) is the point at which both the Sun and its light or brilliance is concealed.
 
091.001-4
"By the Sun and its brightness (splendour, brightness, brilliance - duha) and the moon when it follows it and the day (Arabic: nahar) when it displays it (sun's glory) and the night (Arabic: layl) when it covers / conceals it"

This is the point when the day (nahar), which constitutes both the sun and its light, is completely concealed.  If only the sun is concealed (ghurub), but its light is still evident in the sky as in sunset, this is arguably not complete 'layl' (night)

Source: http://quransmessage.com/articles/fasting%20till%20night%20FM3.htm

"sun/shams" is a feminine noun. "brightness/duha" is a masculine noun. Thus:

[91:1] By the sun and its brightness.
[91:2] And the moon that follows it.
[91:3] And the "nahar" (day) that reveals it.
[91:4] And the "layl" (night) that covers it.