# Cycles light intensity units

Hi everyone, I wonder if there is a relation between cycles light intensity numerical value and some phisical unit. Just like linear distance units (1 BU = 1 m) I wonder if they used some convention like intensity 1 is 1 cd/m2 for area lights. So if i model a light bulb and assign an emission shader with the same intensity of the real thing i can get plausible and coherent light intesity in a scene. Same for sun lamps (maybe lux are more appropriate for this kind of light).

Thanks in advance!

Quote from here:

"Cycles lamp strength for point, spot and area lamps is specified in Watts […]. For Cycles this means you typically need higher values, as you couldn’t use a 1W lamp to light a room, you need something stronger like a 100W lamp.
[…]

Sun lamps in Cycles are specified in Watts/m2, which requires much smaller values like 1 W/m2. This can be confusing, but specifying strength in Watts wouldn’t have been convenient, the real sun for example has strength 384600000000000000000000000W. Emission shaders on meshes are also in Watts/m2."

And setting the intensity to1 gives you accurate appearance of light color in final render somehow (from docs, too)

The feedback speed of this forum is incredible, thanks guys.

Fixed power for area and point seem to be convenient for certain cases.
It would be nice to be able to choose if you want to keep the global power of an area light or increasing it when icreasing size, for example:
a) I could express the power of the area light in Watts (current behaviour), so it’s a fixed value, in this case if I make the light bigger, the power would be distributed evenly on the area light and the total power is the same.
b) Express the power of the area light in Watts/squaremeters so the total power will depend from the area of the light (just like the current behaviour of an emission shader)

There’s some renderer that allowed this but I couldn’t remember wich one.

What about the world emission intensity?

Gleb, what do you mean? Intensity to 1 of what kind of light? And what do you mean for accurate light color apeearance?