Here is a plant that was known to be afflicted with light burn. Notice how the damage is also on bottom leaves:
View attachment 1263954
And here's a plant with leaf damage known to be caused by Potassium deficiency. The light was definately not too intense but the worst leaves were still towards the top:
View attachment 1263955
In some cases like this one, Potassium deficiency can look just like light burn. When a Phosphorus deficiency is involved as well, the damge can be crispy like bad light burn. The way you tell the difference is by knowing how close the plants can be to your light. If the damaged leaves are far enough away, you know it's not light burn.
If it is a Potassium problem it is not a deficiency ... it is an overabundance.
When you have too much Potassium in your soil, it can lead to big troubles, like salt damage and acid fixation of the root system,
as well as too much potassium can cause a calcium deficiency. Your fan leaves will show like a light to a dark yellow
to whitish color in between the veins. Due to a molecular imbalance, potassium toxicity can cause a reduced uptake and lead to the deficiencies of Mg, and in some cases, Ca. Also leads to the other nutrients to not be absorbed properly leading to lots of other deficiency such as: magnesium, manganese, zinc and iron and can cause problems with calcium as well.
If there is a Potassium deficiency in plants it causes the plants leaves to show retarded growth
and show a scorched tip and edges around the leaves. Plants may stretch and your branches can be easily broken or weak. Don’t get this deficiency confused with iron, because it almost acts like iron but to tell the difference in the two is:
for potassium the tips of the leaves curl and the edges burn and die. Older leaves may show a red color and leaves could curl upwards. Dead patches (Necrosis) can happen on the margins of larger fan leaves thus, the leaves will eventually die off and turn brown. The Older leaves will show different patches of color (mottle) and turn yellow between the veins, following by whole leaves that turn dark yellow and die.
Still it does look like light bleaching.
This picture is what light bleaching/ light burn looks like.
Only way to fix this is to Move the lights away from the plant!
Or make sure you don't go over 75 watts a sq foot, or your plant will have to much light and light bleaching can occur anywhere on the plant. (indica species seem to bleach easier than sativas imo.)
(Picture Provided by Boy Howdy)
Pictures, closer and clearer and from different angles, not taken in HPS light would be helpful.
