Science - Light Questions.
polycounter lvl 11
This is sort of a generic science question, not app-specific. Science Nerds, prepare yourself...
I'm trying to find a table of light sources by apparent brightness. I'm trying to use a standardized scale for Emissive/Glow/Self illumination Maps based on apparent brightness. So, say you're painting emissive maps for the sun, a flashlight, a streetlight, a car's headlight, a window.... all of those have fixed values on a scale of 0-1 based on some unit of measurement.
#1 - I can't find the right form of measurement; am I looking for Lumens, Lux, Candelas, what?
#2 - I'm hopefully looking for a list of what all of those would come out as. Like, is a headlight 40,000 Lumens, versus the sun is 100,000? A grid or table or list of these values would be super awesome.
I looked around a bit and got lost in Lux, Lumens, Candelas, and confusing equations. I can do math between them if I know what measurement it is I'm really looking for, but a lot of the definitions of light are somewhat vague and interrelated, so I'm not really sure which I'm actually after. Any help would be appreciated. Thanks in advance!
I'm trying to find a table of light sources by apparent brightness. I'm trying to use a standardized scale for Emissive/Glow/Self illumination Maps based on apparent brightness. So, say you're painting emissive maps for the sun, a flashlight, a streetlight, a car's headlight, a window.... all of those have fixed values on a scale of 0-1 based on some unit of measurement.
#1 - I can't find the right form of measurement; am I looking for Lumens, Lux, Candelas, what?
#2 - I'm hopefully looking for a list of what all of those would come out as. Like, is a headlight 40,000 Lumens, versus the sun is 100,000? A grid or table or list of these values would be super awesome.
I looked around a bit and got lost in Lux, Lumens, Candelas, and confusing equations. I can do math between them if I know what measurement it is I'm really looking for, but a lot of the definitions of light are somewhat vague and interrelated, so I'm not really sure which I'm actually after. Any help would be appreciated. Thanks in advance!
Replies
Yeah, any summary would be awesome. Thanks!
The Photometric unit you're looking for is Luminance [cd/m^2], where cd are candela, measure of the Luminous Intensity and m^2 are the apparent surface in the Luminous Intensity direction, you usually got it by multiplying the surface area by the cosine of the angle between the normal to surface and the viewing direction. Keep in mind that Luminous Intensity is expressed by a vector, the sum of all vectors describing Luminous Intensity is the Photometric Web.
Luminance [cd/m^2] = Luminous Intensity / Apparent Surface
Luminous Intensity [cd] = Luminous Flux [lm] / Solid Angle of emission [omega]
Give the internet a go starting from these elements, and you should be able to figure out what you need.
Sync - I was thinking Candelas and Luminance sounded similar; glad to hear they're related. The problem I have is that the sun is apparently 400 Billion Candelas, based on size. So it'd technically be emitting 40 Million times more light than a 10,000 Candelas streetlight. However, at our position on earth, it doesn't appear 40M times brighter; would you calculate the sun's total Luminence based on it's total size, or would there be a size based on it's apparent size in the sky?
The eye can adapt to see different Luminance magnitude orders, so the sun looks really almost bright as a candle at night, but is a wonderful ability of human eye. And if you want to calculate sun Luminance I think you should use its actual dimensions, like when you get the apparent surface by the cosine you don't take into account perspective, distance and so on.
Part of why I want a fixed value is because we're doing light mapping, so the Sun/Candle effect you're talking about would be accounted for if the values of the sun and candles are calculated correctly. It's also why I don't want to just guess the values, because while a Candle may not appear very bright at daytime, it'd appear bright at night if it was the only light source in a dark room. Knowing that actual values will help determine the rest of the calculations.
I hope that helps.