I am pleasantly surprised by your third image, I would have not expected that result.
To answer your main question, the LED lighting up (even that dim) indicates the presence of voltage and current. However, the dimness also indicates how little current is present.
The electronics explanation of what's going on is that the photons from the light are generating a current in the diode. Each diode that's getting illuminated electrically looks a bit like the schematic below:
simulate this circuit – Schematic created using CircuitLab
Depending on the diode you used, that forward voltage may be around 0.6 - 0.8 V. Without a load, the generated photo current will just flow into the diode. While 30 V sounds suspiciously high for the circuit you have drawn (I would expect maybe 6-8 V instead), you should be able to measure that voltage. This is the open circuit voltage, as there is no load.
If you load down the output, maybe even using a microamp scale on a multimeter, you can see the maximum current your array will provide under those conditions.
The LED lighting tells me that your voltage is probably better than 2.0V, and maybe 1-10µA of current is flowing, which is not a whole lot of power. There are a bunch of things that are hindering how much power you can extract from this setup, here are a few:
- Exposed Area - Each one of those diodes has maybe 1 mm^2 of silicon in it. Probably half of it isn't facing the light, and a good chunk may be covered by opaque materials, such as aluminum.
- Illumination Intensity - Typically, indoor lighting is pretty dim compared to the sun. The current output is mostly proportional to the amount of light that hits each of the diodes. If you took it outside, you would get more power under direct sunlight.
- Angle of incidence - The angle that the light hits the diode should be perpendicular (90 degrees) and this will be difficult to align for each individual diode
These issues are why this diode array will never out-perform a solar cell of the same shape and size - the solar cells have been optimized for turning light into power, and these diodes have been optimized for being electrical diodes.
