# The correct quantity

R

#### Richard

Jan 1, 1970
0
I'm looking at a technical data sheet concerning signage. There is a graph
showing "Light output" in lux, versus "Position across sign".

The lux value for the middle of the sign reads about 2K lux.

Just checking: "Light ouput" is a measure of Luminance Emittance is it not?
TIA.

D

#### Douglas G. Cummins

Jan 1, 1970
0
Light Output is a broad generic term. For example:

Illuminance (Lux) is the measure of light over an area (light flux per
unit area, also called flux density) - the light output on an object.

Luminance (Cd/m2) is the measure of light in a viewing angle (flux
density per unit solid viewing angle) - the light output from a large
area light source.

Luminous Intensity (Cd) is the measure of radiometric power per unit
solid angle - the light output from a point source in a single direction.

Luminous Flux (Lumen) is the measure of total radiometric power - the
light output in all directions.

R

#### Richard

Jan 1, 1970
0
Hi.

The technical article relates to acrylic sheet made to be edge-lit.

The graph is made with the condition that the signage is edge-lit with two
T5 HO flourescent tubes spaced 650mm apart. No mention is made of the
wattage or the part number of these T5 HO tubes or their length.

However, I think the graph is trying to give what constitutes useful
information and I think in the circumstances that will be brightness of the
signage across it. It seems to me then that the measure is very probably
lumens per square meter. This corresponds to Luminous Emittance. That would
be Illuminance if we were talking of light incident on a surface.

V

#### Victor Roberts

Jan 1, 1970
0
Hi.

The technical article relates to acrylic sheet made to be edge-lit.

The graph is made with the condition that the signage is edge-lit with two
T5 HO flourescent tubes spaced 650mm apart. No mention is made of the
wattage or the part number of these T5 HO tubes or their length.

However, I think the graph is trying to give what constitutes useful
information and I think in the circumstances that will be brightness of the
signage across it. It seems to me then that the measure is very probably
lumens per square meter. This corresponds to Luminous Emittance.

In the US at least, more properly called "luminous exitance"
these days. The IESNA says that the term luminous
emittance was formerly used but is now is depreciated.
That would
be Illuminance if we were talking of light incident on a surface.

But many people would still use the term illuminance.

--
Vic Roberts
http://www.RobertsResearchInc.com
or use e-mail address listed at the Web site.

This information is provided for educational purposes only.
It may not be used in any publication or posted on any Web
site without written permission.

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