Silly idea. I have seen some low power LED lights on adjustable arms. They are fairly small in size. What would happen if you positioned them inside your plant close to the main stem? Maybe do some pruning to make space.
I’m not a light expert but your idea is not silly at all. What you are describing is making LED closer to the plant and reducing its power.
Light is basically an energy source for plants to make hem synthesize the food and live. We can measure the light density reached to the plant and that’s why we use bigger lights for bigger tents. As long as you provide sufficient levels and measure what you are giving (PPFD, PAR, DLI, etc), it can work.
The problem is measurement. I believe accurate measurement of such values is expensive and it requires lab-level environment. Assuming you can get a correct measurement, I think placing adjustable arms around the plant and putting smaller, full-spectrum LEDs can work. You can then automate the distance based on the stages of the plant. This eliminates the heating problem generated by the light, and reduces the electricity bill because you give what the plant needs on a small surface. Current light equipment lights the entire room, which is inefficient.
In summary, it can work, but you need good measurement equipment to select best LEDs and positioning, but those equipments can be expensive. Still, a good side project :)
Forgot to mention that this smaller LED idea can work up to some point. These babies grow a lot and at some point we need to cover the whole plant. Unless it’s a modular system where you add LEDs around as the plant grows, conventional full-tent LEDs make sense.
It would work, meaning it would not kill the plant and it would give an increase in productivity, but it's the cost of grams per watts worth your trouble? You should focus instead in acquiring better LED light or improving the reflective surfaces around the grow area instead of another source of light with marginal gains.