I'm studying atomic spectras and got puzzled about light-quantization. I'll expose my effort to understand it so far.
Around the year $1900$ Planck explained blackbody radiation including a term of the form $A=k\,\nu$ which is reasonable because of the experimental results: radiating energy had been shown to decrease with frequency. If I'm not mistaken $k$ was a constant obtained by fitting the experimental data (then called Planck's constant $h$).
A couple of years later it comes the photoelectric effect, which was explained just using Planck's idea and little more. Everyone knows the formula so I won't paste it here.
Does photoelectric effect suggest that light can be thought as particle? How?
I understand perfectly $E=h\,\nu$ and that atoms have quantized energy levels, but is light energy quantized?