How to recognize light deficiency?

[Scapexghost]

Nitrogen, phosphate, iron, and most other nutrient deficiencies can be diagnosed visually, but what about light deficiency? How can you tell if your plants are not getting enough light?

[Guppysnail]

When stem plants grow thick and tall the bottom leave start yellowing and browning sort of melt if you have ever seen it. It is because they are shaded. So if I see other plants doing that near the top I move them to a more lighted area. Not a great scientific explanation but that is how I know. Here is a pic of a plant I just moved a few days ago. This part was against the wall under the filter outlet totally shaded. I need to cut it off but…to do list is long

[Patrick_G]

I don’t have a satisfying answer but you generally check the requirements for each plant vs the amount of light I have. 

@Guppysnail I agree, when the lower parts of stem plants lose leaves and get mushy that’s a good indication they need more light. I usually cut off the top part and replant. 

Edited November 18, 2021 by Patrick_G

[Streetwise]

Another metric would be algae and biofilm growth to support shrimp fry.

[Tanked]

For me lighting is the most confounding part of this hobby.  If your water is good, than the two easiest things for me are: the plants don't grow, or The stem plants grow tall but do not branch out because they are stretching toward the light.