Dark green foliage + some clowing on the leaves = Nitrogen excess , I feel like you could experiment a N excess but it's not the answer to your question.
The fact that the yellowing in not starting from the bottom leaves to spread to the upper leaves makes me think that it is not a primary element ( N P K ) or a secondary element ( Cal / Mag / S ) deficiency , it would have start with the bottom leaves first so I feel like you have a trace elements deficiency , which one ? I'm not specialist enough to tell you that , sorry .
Looks like a K deficiency ( potassium ) but the older leaves would have been afected
It's not a light burn like you said , my Sticky beast started to burn when she was 5 cm away from my mars TSL1000 and even at 10 cm it takes a couple days before the burnt become serious ( and by serious I mean soft , I know what a hps burn can do so this one is a soft one )