![]() ![]() This ratio of lumens to Watts is the luminous efficacy, not to be confused with luminous efficiency, noted earlier. With LED bulbs being 6x or more efficient converting power to light than incandescents, you’ll see “ 60W equivalent – 800 lumens” on packaging, since such LEDs actually draw around 9 Watts. This rating refers to the incoming amount of power, not what the bulb itself produces. Incandescent bulbs are (were) sold as “60 Watts” or similar. Think of it as the number of photons emitted per second, again modulated by the luminous efficiency function. Luminous flux: measured in lumens, this is what you’ll see on the box for most light bulbs you buy nowadays. All the units that follow are in terms of “per second,” and those are the ones you’ll see used in describing lights in the real world and computer graphics. power) get used for light in the field of computer graphics. I say “forget them” as far as graphics goes – I’ve never seen energy (vs. ![]() Luminous energy: same, modified by the eye’s response. Radiant energy: like it says, energy, some total amount of radiation, basically. Well, some of the links below may inform and entertain. photometry factors in how our eyes respond to light, described by the luminous efficiency function (well, functions: there’s the photopic function, for brightly lit conditions, and the scotopic, for dim). Radiometry is concerned with any electromagnetic radiation – radio, microwaves, x-rays, etc. You’ll see similar tables in many other places, including page 272 of our own book. I may still have a bug or two in this post (though am trying hard not to), so tell me if I do and I’ll fix it: PBR book gives the textbook basics, starting with radiometric units and going on to photometric. My thanks to Luca Fascione and Anders Langlands in particular for correcting me along the way. Lux, in particular, is a term where I have been misled by many pages on the internet that attempt to define it. Some of this knowledge was hard won, for me. My focus is on the practical, real-world use of these units. So, here’s my summary of the four main light units, with others mentioned along the way. APIs and programs with “0.7” or “90% brightness” or other relative units don’t hack it, as they are not anchored to any physical meaning. These past months I’ve been learning a fair bit about this area, as proper specification of lights is critical if you want to, for example, move a fully modeled scene from one application to another, or are merging real-world data with synthetic. That’s all most of us normally need, to be honest. My usual attitude with lights was (and still is, most of the time), “make them brighter” if the scene is too dim. This was, at least, my level of understanding for the past lessee 38 years I’ve been in the field of computer graphics. We have some sense of what lumens and candelas are about, we’ve maybe heard of nits with regard to our monitors, and maybe have a vague sense of what lux is about. ![]() I expect most of us have a passing knowledge of physical units for lights. ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |