In a glass of water, if alcohol accounts for 2%, the water’s saturation is 98%. If alcohol makes up 10%, the water’s saturation is 90%. Now, imagine a semipermeable membrane that filters out alcohol—but with a side effect: it also removes some water. This membrane can boost the water’s saturation.
Take 1 liter of water with 10% alcohol (90% water saturation). Using the membrane to filter out the 10% alcohol also removes 20% of the water. The result? The water’s saturation reaches 100%—it becomes purer—but the total volume of the solution shrinks to 70% of the original.
Applying This to Projectors
Think of green light as water and yellow light as alcohol. Green light is mixed with yellow light. The total brightness is high: suppose the luminous flux is 1000 lumens, but 20% of that is yellow light. As a result, the green light saturation is only 80%.
If you use a filter to remove the 20% yellow light—but it also filters out 10% of the green light—you get a purer green signal with 100% green saturation. However, the total brightness drops to 70% (700 lumens).
The same logic applies to red light: it will also become purer, with higher saturation, as red light is often mixed with yellow light. But if you use various filters to strip out all unwanted colors from white light—orange, yellow, green, cyan, blue, purple—leaving only red, the red light saturation hits 100%.
Projector manufacturers sometimes use mixed light to inflate brightness at the cost of inaccurate colors. When they prioritize accurate color reproduction, the brightness suffers miserably! 😄