;;; -*- lexical-binding: t -*-
;;
;; this file:
;;   https://dataswamp.org/~incal/emacs-init/lights.el
;;
;; lights:
;;   https://dataswamp.org/~incal/data/LIGHTS

(defun illumination-score (w lm)
  (interactive "nW: \nnlm: ")
  (let*((le (/ lm w 1.0))
        (max   75) ; LED luminous efficacy (lm/W)
        (min   15) ; incandescent ditto
        (scale (- max min))
        (score (* 100 (/ (- le min) scale)) ))
    (format "%.0f%%" score) ))

(when nil
  (illumination-score
   (+ (* 2 1) (* 2 2.8) 8 7) ; 22.6 W
   (+ (* 2 120) 500 525)     ; 1265 lm
   )                         ; 68%
)

(provide 'lights)