Get the luminosity of a hex color with Power Query

fnGetLuminosity.pq

// Calculate luminosity based on hex value
(HEX as text)=>

let 
    // Split strings into list by each character, convert to upper, remove hash
    Source = if HEX <> "" then Text.Upper(Text.AfterDelimiter(Text.From(HEX), "#")) else "#000000",
    
    // Split the Source by each character
    SplitHex = Splitter.SplitTextByRepeatedLengths(1)(Source),

    GetLuminosity = (hexlist)=>

        let 
            // Build the RGB list
            RGB = List.Combine({{"0".."9"},{"A".."F"}}),
            
            // Sub function to figure out complimentary color RGB value
            GetRGB = (cval1, cval2)=>
            let 
                RGBVal = (Number.From(cval1) * 16)+ Number.From(cval2)
            in       
                RGBVal,
            
            
            // Get positions of each digit
            r = GetRGB(List.PositionOf(RGB,hexlist{0}), List.PositionOf(RGB, hexlist{1})),
            g = GetRGB(List.PositionOf(RGB, hexlist{2}), List.PositionOf(RGB, hexlist{3})),
            b = GetRGB(List.PositionOf(RGB,hexlist{4}), List.PositionOf(RGB,hexlist{5})),

            
            // Combine R,G,B hex values to one hex value
            FinalRGB = {r,g,b},
            
            // Get the luminosity
            Luminosity = 0.5 * (List.Max(FinalRGB)/255 + List.Min(FinalRGB)/255)
        in
            Luminosity,
    
    // Process the split list from the input
    lum = GetLuminosity(SplitHex)

    in

lum