Does light loose energy as the distance increases, or does it stay the same

I performed a lab in class, where i tested the oxygen produced from elodea at given distances from a 75 watt light bulb. Those distances were 10, 35 and 75 cm.
BUT... my table's experiment ended with all three distances producing .5mm, which I can't help but think was inaccurate.

Light intensity diminishes with distance squared (the total energy is constant, but it spreads out). It may be that your light source does not produce the mixture of wavelengths necessary for photosynthesis. What you may be measuring is the result of ambient light or dissolved gas.

The lightwave itself stays as energetic (same wavelength), but the intensity does decrease because you're simply getting less photons. Think of the sun... super bright star that's close to earth. Now thinnk of all the other stars... just as bright (some are much brighter), but they're so far away you're not gonna get much energy from them for solar power or plant photosynthesis.