When looking at SMD LEDs, you may sometimes find reverse mount SMD LEDS such as the IN-S124BRR reverse mount SMD LEDs from Inolux, below.
Reverse mount SMD LEDs are commonly designed to emit light through a small cut-out hole in the PC board.
When looking at the reverse mount SMD LEDs in Digi-Key’s website, you can identify these parts by the descriptor “Bottom Entry” in the Mounting Type filter field.