专业资料

Color Temperature

The intrinsic color of the light warmth or coolness emitted by a lamp. It is measured in degree Kelvin(K). The higher tempreature, the “cooler” (whiter) the light.

Color Rendering

The degree which light enable human eyes to perceive colors correctly, as it would in natural daylight.

Color Rendering Index

Color Rendering Index (Ra) is a measure between the color of an object (its self-luminous color) and its appearance under a reference light source. The best value of Ra is 100, the smaller the discrepancy, the better the color rendering property.

Beam Angle / Field Angle

The angular dimension of the cone of light encompassing the central part of the beam arc to the angle where the intensity is 50% of the maximum illuminance which field angle requiring 10%.

Cut-off Angle

Cut-off angle is formed between the ceiling and the imaginary straight line tangent to the lamp and passes the edge of the reflector. If our visual field is situated within this angle, it is impossible to see the lamp.

Glare

Glare is defined by the IESNA as “…the sensation produced by luminance within the visual field that is sufficiently greater than that to which the eyes are adapted” Glare can cause fatigue, headaches, annoyance, discomfort and productivity loss due to reduced visual performance and visibility. There are two types of glare, direct glare and indirect glare. Direct glare is caused by high luminance directly in the field of view. Indirect glare, also known as veiling reflections, results when luminance from an overhead fixture reflects on a shiny surface and reduces visibility and contrast.

To reduce glare

  • Choose luminaires with deep reflectors that block the lamp from the field of view
  • Choose fixtures with louvers or lenses to conceal the lamp
  • Decrease the luminance of the source by using lower wattage lamps and spacing fixtures closer together
  • Select fixtures with adequate shielding or diffusing media such as low bays or shielded fluorescents
  • Re-position the lighting fixture or the task so that the reflected image is directed away from the observer

Downlight and Wallwasher

Standard Downlights give the light which integrates an open reflector and / or shielding device, usually recessed, whose light spread forms a cone shape and directly downward, recommended for use in horizontal planes.

Wallwasher downlightings are mostly recommended for the combination of lighting walls and floors. These lights with asymmetical reflectors provided, when properly positioned, an optimum light distribution covering different points of wall and floor.

Uniformity

The uniformity of illuminance is a quality describing how evenly the light spreads over an area. Although a room’s average illuminance may be appropriate, two factors may pose a danger on the uniformity.

  • Improper fixture placement based on the luminaire’s spacing criteria
  • Fixtures that are modifies with reflectors narrow the light distribution
    In case of non-uniform illuminance occur, several problem will come out:

 

  • Inadequate lighting levels in some areas
  • Visual discomfort when tasks frequent moving from underlit to overlit areas
  • Bright spots and a patch of light on floors or walls cause distraction and generate low quality appearance

 

Safety Classes

Class 1:
Luminaire in which protection against electric shock does not only rely on the basic insulation, but also on the additional safety insulation that are provided for the connection for the accessible conductive parts to the protective conductor in the fixed wiring of installation that the obtainable conductive parts cannot become live in case of a failure of the basic insulation.

Class II:
A luminaire in which protection against electric shock does not only rely on the basic insulation, but also on the additional safety insulation, such as double insulation or reinforced insulation, being no provision for protective earthing or reliance upon installation condition.

Class III:
Aluminaire in which protection against electric shock is based on the safety extra low voltages (SELV) or in which voltages higher than SELV are not generated. The SELV is defined as a voltage which does not exceed 50V r.m.s. at alternative current between conductors or conductor and earth in a circuit. A class III luminaire must never be provided with earthing.

Index of Protection

A Protection degree, usually use in Europe, offered by the fixture to the ingress of the solids and liquids is indicated by the prefix “IP” followed by three numbers. The first number means the degree of protection against the entrance of solids and the second one of liquids. The third figure indicates the degree of proofing against mechanical damage. Most of the lighting companies would use 2 digit (first and second) rather than 3 digit for their product.

Performance Cone

The illuminance values given (lux/klm) are the maximium values within the beam angle for horizontal planes at various distance below the luminaire. The diameter of the beam, i.e the approximate size of the light coverage, is also given.