Glow lichen not generating below y=0

Summary:

When exploring the new caves i noticed that it was too dark below y=0
And there are no glow lichen anywhere but i see some above y=0

Steps to reproduce:

1. Load up a world with the caves and cliffs experimental on
2. Go to -levels of the world
3. Look if there are any glow lichen around
4.there isn't

Expected results:

Glow lichen should also generate below y 0 Just

Observed results:

No glow lichen was generated