10 List of abbreviations. Osram HQI-E 150 W/NDL CL
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OSRAM metal halide lamps comply with the limit values of 2 mW/klm or even go below the limit considerably.
Exceptions are the HQI ® lamps without outer bulb with the power of 1000 W and 2000 W. Here special safety precautions have to be met by the luminaire.
Fading occurs not only due to UV but also with shortwave visible light, depending on the spectral object sensitivity (effect function) of the irradiated object.
There is plenty of information on this subject in the
Division 6 report of the CIE (CIE technical collection) entitled “On the Deterioration of Exhibited Objects by
Optical Radiation”. Although this deals with objects in museums, the results are also applicable for example to shop window lighting. A stronger fading effect could be achieved by stronger focusing of the light or by a higher luminous flux in the lamp.
Standardization of UV variables per “klm” or “lm” offers the advantage of being able to make direct comparison of the relative radiation shares of various lamp types and wattage classes with regard to the same application illuminances.
As a comparison:
• Tubular Fluorescent T8 & T5 have an ACGIH UV value of approx. 0.2 mW/klm (with possible minor fluctuations depending on wattage class and light colour).
• Compact lamps have a lower 0.03 mW/klm
A numerical definition of colour change generated by irradiation must be expressed in the form of colourimetric differences ΔE* ab
. In this way, it is possible to express exactly every fading, blackening and yellowing or basically every colour change. Effective radiation resulting in a colour change of exactly ΔE* ab
= 1, is called threshold effective radiant exposure. This value is important, as experience shows that colour changes in this magnitude can be perceived by the average observer on comparing unexposed areas of a sample with exposed parts.
Other limit values can be used (ΔE* ab
= 2, 3, 4, etc.) if the correspondingly larger colour differences are acceptable.
8.4.2 Protective measures to reduce fading
Every protective measure must refer to a reduction in effective radiant exposure Hdm. Effective radiant exposure Hdm is the product of the radiation time tdm and effective irradiance Edm.
Fig. 55: Evaluation function for the sensitivity of human tissue to UV radiation as per ICNIRP
8.4.1 Fading effect
The colour change in light-sensitive materials resulting from irradiation with light sources depends on
• irradiance or illuminance,
• spectral distribution of the radiation from the light source,
• spectral object sensitivity (effect function) and
• irradiation time.
If daylight contributes to the lighting e.g. via skylights or shop windows, this has to be considered as part of the irradiation as well. Daylight contains considerable amounts of light in the UV range und short-wave visible light.
Reduction can consist of:
• avoiding the critical wavelengths by using corresponding filters according to the spectral sensitivity of the irradiated object
• reducing the irradiance
• reducing the exposure time
• enlarging the distance to the luminaire
Remarks on filtering the critical wavelengths:
Relative spectral sensitivity for most samples is not only very high in the ultraviolet range of irradiation, and also still fairly high in the visible range for many exhibits. This would mean that the short-wave visible range also has to be filtered. To what extent this is feasible depends on the colour rendering characteristics and the changed colour temperature of the remaining visible radiation.
In new objects, colour change is strongest during the initial period of light exposure. Old wall carpets for example which have been exposed to light for centuries, show hardly any remaining sensitivity to radiation.
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