In the context of Equivalent Melanopic Lux (EML), which expression correctly represents its calculation?

• A. EML equals visual lux plus melanopic ratio
• B. EML equals visual lux divided by melanopic ratio
• C. EML equals visual lux times melanopic ratio
• D. EML equals melanopic lux minus visual lux

Answer: (C)

Equivalent Melanopic Lux is the photopic (visual) illuminance adjusted to reflect how effectively a light source stimulates melanopsin-containing cells. The melanopic response is captured by a ratio that compares melanopic illuminance to photopic illuminance for that spectrum. To express the light in melanopic terms, you multiply the visual lux by this melanopic ratio. If the spectrum is especially good at activating melanopsin, the ratio is higher and the EML rises; if it’s less effective, the ratio is lower and the EML lowers. Using multiplication correctly applies the spectral weighting to the visible light level, whereas addition, subtraction, or division would not correctly translate photopic lux into melanopic-equivalent lux.