This was posted on my PhD blog originally on 1/15/16
Let's zoom into photosystem II to examine how accessory pigments help with light capture. Photosystem II is typically shown in the textbooks as an oval, with the oxygen evolving complex occasionally added as an external oval. The problem with this is that it pays zero attention to the large antenna system that exists with the depicted photosystem II core.
These antennas are several other protein complexes called Light Harvesting Complexes (LHC). The LHC have many chlorophyll and accessory pigments that can absorb light. The energy absorbed is then to their neighbor chlorophylls all the way to the special chlorophyll in the reaction core so that ATP can be made. Think of these pathways as a line of people standing next to each other, shoulder to shoulder, one standing at the goal line. Balls (photons) are tossed randomly at the line and whoever catches one can pass it down along the line of people to the goal. The greater amount people in the line, or even lines, the higher percentage of balls they will catch. For the plant, the increase in surface area due to the LHC allows a high percentage of light to actually reach the goal line of photosystem II.
Carotenes and xanthophylls are two important light capturing pigments. They extend the wavelength range of light the plant can use. There is only difference between carotenes and xanthophylls. Carotenes are made of only carbon and hydrogen, while xanthophylls also contain oxygen. All xanthophylls are derived from carotene precursors in the same fashion as described in my previous post. A few specific xanthophylls are incredibly important for photosynthetic regulation. Their names are: violaxanthin. antheraxanthin, and zeaxanthin. But as my son would say, we'll just call them V A Z "for short".
Photosynthetic stressors generate excess amounts of reactive oxygen species, including singlet chlorophyll. This decrease the pH triggering the conversion of V to Z. The conversion happens quickly, allowing the plant to get rid of excess energy before it can cause irreparable harm.