Mob Farm Spawning Very Few Mobs

  • Hello! Thank you for visiting the forums. You can sign up or log in using the button on the top right of your screen. If you do not have an account consider signing up and joining the forums community!
So I built a basic canal style mob farm with a 22 block drop, however very few to no mobs are spawning. My AFK point is at the bottom of the drop, 23 blocks down from where the mobs spawn, there is no light and I used full blocks. The only light in the picture below is due to me opening the enclosure to take the picture, when closed light=0. Why are so few mobs spawning?
Minecraft 1.13.1 20_03_2019 4_11_44 PM.png
What do you mean by non- effective? How can I fix it? Also any and all light in that pic is due to me opening it to take the screenshot. I have closed it whilst inside and there is 0 light so it’s not there.