# Luminance and illuminance relationship counseling

### Luminance vs. Illuminance

Higher wall luminance in offices result in a higher room appraisal. . In practice, however, horizontal illuminance and wall and ceiling (il)luminance are quite often .. Inter-rater reliability was tested using the intra-class correlation coefficient ( ICC). M. Terman, J.S. TermanLight therapy for seasonal and nonseasonal. Alternatively, the luminance of a surface can be calculated from the formula L = E x A typical luminance for a piece of white paper under an illuminance of bestwebdirectory.info# post- .. Relation, but not a conversion is discussed here.

The principal planes of the lens are represented as lying at PP and at PP', while the entrance and exit pupils are designated as being at NP and XP, respectively, and the principal focal lengths are L and L'.

The point P may be self-luminous or may be illuminated by reflected light. In either case it will illuminate the entrance pupil of the lens NP with an intensity inversely proportional to the square of the distance between P and R, the latter being in the plane of the entrance pupil, and directly proportional to its luminous intensity I.

Let the distance between P and R be X. The distance X may be considered as being made up of two components. The negative sign is required because of the inversion of the image.

The second component of the distance X is the distance LR from the plane of the principal focus to the plane of the entrance pupil. The intensity of the image at P' is inversely proportional to the area of the image.

Of the light incident upon the lens, some is absorbed, but a greater part is reflected from the lens surfaces, especially if these are uncemented. The quantity of the emerging light is always less than that incident upon the system and is proportional to the incident light and the transmission of the lens system T. Consequently I' is proportional to T.

## Luminance vs. Illuminance

Having discussed briefly the separate factors which influence the intensity of the image, we may now combine the separate effects. For objects considerably off the optical axis, and especially when the view angle is large, the intensity of the image at a corner of the plate may vary considerably from that given by Eq. By definition the f-number of a lens is the ratio of the focal length to the diameter of the aperture.

If not, why not? Got a confirmation here: For a while they had it as "divided by 2pi" but after discussion they agree with the prior link. I'll mark this post "question answered" if I can.

Ted xpatUSA's gear list: The same poster, Andy, gave you a better answer in the 4th post there: Illuminance and luminance measure different things. Even then, you have to specify the solid angle over which you are measuring the reflected light, while the falling light can be one-directional, or not.

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They are just different animals. Even then, you have to specify the solid angle over which you are measuring the reflected light, No you don't, it cancels out.

I specified lambertian so it's not.

- What’s the difference between Luminance and Illuminance?
- How to convert illuminance to luminance?

Sure but it still applies in this case. In fact, it's even distance independent even though it involves illuminance. I was talking about the incident light.

**Luminous Flux, Luminous Intensity and Illuminance of Light**

Perhaps you are not familiar with a lambertian distribution or maybe we are not talking about the same thing. When light falls on a lambertian surface, it reflects in all directions with intensity equal to the cosine of the angle intensity drops with the cosine of the reflected angle. The larger the angle, the larger the area. That's where the two cosines cancel, resulting in equal luminance regardless of angle. A radian is measured in the two-dimensional plane. A steradian is similar to a radian, only measured in three dimensions.

The definition of a steradian is as follows: One steradian is a circular patch on a sphere's surface who's area is equal to the square of the radius of the sphere.

### Luminance vs. Illuminance Relationship

A steradian is an odd "projection" of a 2D subtended angle into three dimensional space, or what is called a solid angle. The intersection of the 2D angle with the sphere's surface intersects a circular patch which is itself bisected by the radian arc. Another term for it is squared radian.

The solid angle that represents one steradian is computed as: To complete the definition of a steradian in relation to a sphere: One might look at that another way: Now that the definition of a steradian is out of the way, we can come to a clearer understanding of the relationship of a lumen to a candela.