As previously established, the light output of the WLE system scales linearly with the number of light emitters over a wide range. It is convenient to express the number or emitters 𝑛 𝑊𝐿𝐸 as the dimensionless fill factor (FF) which corresponds to the volume of emitters to total occupied reactor volume, eqn. 1, where 𝑉 𝑊𝐿𝐸 is the volume of each emitter (0.52 mL) and 𝑉 𝑅 is the volume of the liquid reaction mixture. In relation to the FF, the photon flux density 𝑞 𝑝 scales exponentially due to the increased light power in combination with the volume displacement of the emitters themselves, eqn. 2, where 𝑞 𝑊𝐿𝐸 denotes the average photon flux emission from each individual emitter, which can be obtained by fitting this equation to the experimental values.