Joint Lighting

Joint Lighting

 * Joint lighting is the simultaneous lighting of an area with both artificial light and daylight.
 * This type of lighting is much more favorable than complete artificial lighting as it includes a number of the natural spectra of daylight.
 * Even good artificial light is inadequate as a substitute for daylight.
 * Joint lighting has the advantages of both day light (spectral composition, variability) and artificial light (adequate intensity).
 * Obviously a higher concentration of daylighting than artificial lighting is preferable.
 * Mixing ratio of daylight and artificial lighting should be at least 1:1. At a ratio of 1:5 and less, the test results differ very little from results obtained in artificial lighting only.
 * Measurement and evaluation of the joint lighting is not easy. It consists of a constant component and a large amount of variability and spectral composition.

Glares (dazzles)

 * Difficulty seeing in the presence of bright light such as direct or reflected sunlight or artificial light such as car headlamps at night.
 * Can be caused directly by a light source, or by its reflections on surfaces with a higher reflection factor.
 * Glare is caused by a significant ratio of luminance between the task (that which is being looked at) and the glare source.

Types of Dazzles
1. Dazzle by Critical Brightness
 * Direct sunshine – the eyes cannot adapt and the person cannot see well.
 * Critical value of brightness ranges from 200 000 to 1 000 cd.m−2.

2. Transitory Dazzle
 * Due to sudden change of brightness, going from inside to bright outside. The eyes take some time to adapt.
 * There is a sudden change in brightness of the visual field at a rate greater than 1:100.

3. Dazzle by Contrast
 * When there are surfaces of various brightness. The eye cannot adapt to both and a dazzle occurs e.g. bulb fiber on wall.

Glare Reduction
Glare can be reduced using a number of methods:
 * Sunglasses – polarized sunglasses are designed to reduce glare caused by light reflected from surfaces such as water – used mostly by fly-fishers.
 * Some cars include mirrors with automatic anti-glare functions.
 * Anti-reflective treatment on eyeglasses reduces the glare at night

Related articles

 * Issues of Day Lighting, combined illumination. Visual Stress
 * Issues of Artificial Illumination