Determine if a UIColor is light or dark

TextColor.swift

// Returns black if the given background color is light or white if the given color is dark
func textColor(bgColor: UIColor) -> UIColor {
    
    var r: CGFloat = 0.0
    var g: CGFloat = 0.0
    var b: CGFloat = 0.0
    var a: CGFloat = 0.0
    var brightness: CGFloat = 0.0
    
    bgColor.getRed(&r, green: &g, blue: &b, alpha: &a)
    
    // algorithm from: http://www.w3.org/WAI/ER/WD-AERT/#color-contrast
    brightness = ((r * 299) + (g * 587) + (b * 114)) / 1000;
    if (brightness < 0.5) {
        return UIColor.white()
    }
    else {
        return UIColor.black()
    }
}

UIColorIsLight.swift

// returns true if color is light, false if it is dark
extension UIColor
{
    func isLight() -> Bool
    {
        // algorithm from: http://www.w3.org/WAI/ER/WD-AERT/#color-contrast
        let components = CGColorGetComponents(self.CGColor)
        let brightness = ((components[0] * 299) + (components[1] * 587) + (components[2] * 114)) / 1000

        if brightness < 0.5
        {
            return false
        }
        else
        {
            return true
        }
    }
}

isn't working, alpha was skipped