A photosynthetic light-harvesting complex (LHC) is a ring/lattice of chlorophyll pigments surrounding a reaction center (RC). A photon excites one pigment to a singlet exciton state, which then migrates between neighboring pigments by Förster Resonance Energy Transfer (FRET), a dipole–dipole coupling whose rate falls off sharply with distance:
k_FRET(r) = k0 · (R0 / r)^6
k0 = coupling prefactor (site rate constant)
R0 = Förster radius (typical transfer distance)
r = donor–acceptor pigment separation
Real antennae are built as an energetic funnel: pigments further from the RC sit at slightly higher excitation energy than pigments closer in, so transfer is biased downhill. This model adds a detailed-balance factor to the hop rate:
k(i→j) = k_FRET(r_ij) · exp(−max(0, ΔE_ij) / kT)
ΔE_ij = E_j − E_i (uphill hops suppressed, downhill hops favored)
Each exciton also has a constant per-site chance of being lost to fluorescence or heat — including non-photochemical quenching (NPQ), the plant's protective valve that dumps excess excitation as heat under strong light. At the RC, the exciton competes between quenching and irreversible charge separation (trapping), which is what actually drives photosynthesis. The simulation runs this as a continuous-time Monte Carlo process on the pigment network every frame.
- Light intensity — rate of new excitons entering the antenna (photon absorption).
- Antenna rings — size of the pigment network (hop count to the RC grows with radius).
- Förster coupling — the k0 prefactor: raises every hop rate, so excitons migrate faster.
- NPQ quenching — the loss rate competing against trapping; real leaves raise this under bright light to avoid photodamage, at the cost of quantum yield.
Quantum yield Φ = fraction of excitons that reach the RC and are trapped rather than lost, the same figure of merit ecophysiologists measure with PAM fluorometry on real leaves.