Joint Lighting

Joint Lighting[edit | edit source]

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.

Roy Thomson Hall glare

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.

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.

Guillermo Quiroz sun glasses

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

BENCKO, Vladimir, et al. Hygiene and epidemiology : selected chapters. 2. edition. Prague. 2008. ISBN 80-246-0793-X.