The horizontal activity plane is also incorrectly referred to as the workplane. A horizontal activity plane in work settings is the horizontal surface where light is most critical such as the tabletop, desktop, etc. In transition and circulation space, the floor qualifies as the horizontal activity or workplane [1]. In churches or auditorium, laps qualify as the horizontal activity plane. When performing lighting calculations, the calculation points are placed on the horizontal activity plane to observe the distribution of light where it is most needed.


Glare is a result of extreme luminance within the normal field of view. It is dependent upon the position of the user. Moving the user or the object being viewed from the offensive zone can reduce or eliminate glare. Alternatively reorienting the light source can get rid of glare.

Direct glare [2]

How is it caused
Excessive light misdirected towards the eye. Such as automobile headlights, sunlight when looking directly at the sun, etc.

(a) To limit the amount of light directed towards the eye.
(b) To increase the area from which light is emitted thus diffusing it.
(c) To change the direction of the light beam.

Indirect or reflected glare [3]

How is it caused
Excessive uncontrolled luminance reflected from objects or surfaces in the field of view.

(a) Remove glossy areas in the visual task areas as much as possible.
(b) Reconfigure luminaire location to the sides of the task surface so that light is not reflected into the worker’s eyes.

Figure L-VF2: Indirect glare or veiling reflection caused by the reflection of light from a glossy surface
Video Display Terminal (VDT) related glare [4]

How is it caused
This is a type of reflected glare. It is caused by screen reflections into the worker’s eyes that interfere with the view of the screen.

(a) repositioning the screen.
(b) adjusting the angle of the screen.
(c) blinds on windows causing the glare.
(d) dark clothing for workers.
(e) use of deep-cell parabolic louvers on the ceiling.

Figure L-VF3: The glossy surface or a laptop screen reflects the ambient light in the space, making it difficult to view the screen content.