Conclusions
The most important considerations for a museum when selecting a window film are the overall amount of UV blocked, the steepness and location of the cutoff curve, and the color appearance. Table 2 lists these properties for all the films evaluated. By setting 95% as the minimum acceptable
UV rejection level for the 300-400 nm range and 390-410 nm as an acceptable range for the midpoint of the cutoff curve, the list of films suitable for museums can be narrowed down.
In contrast to the findings published previously (6), this study found all of the 3M films to perform well enough for museum use. These films rejected at least 97%, and most
more than 98%, of the UV radiation below 400 nm, and the Prestige line had the steepest cutoff curve of any of the films evaluated. The only potentially objectionable trait of these
films is their tint: 3M does not produce a highly transparent UV-blocking film and the Night Vision line is mirrored, which may not be appropriate for museums.
The 3M films have their UV absorbers incorporated into the adhesive. Previous studies (2, 6) have indicated that this is less desirable than having a separate UV-blocking layer, leading
to worse performance and longevity, but no experimental support has been given for this assertion. Our findings show that the 3M films performed more uniformly well than any other brand, despite having UV blockers in the adhesive; the second part of the study will evaluate their longevity.
Most of the Llumar and Madico films were found to be acceptable,in agreement with the earlier study, but several of these films rejected less than or exactly 95% of the UV light.
Films from these manufacturers should be evaluated on a case-by-case basis. CPFilms, Llumar’s parent company,also owns Vista. The single Vista film evaluated performed well, but generalizations about the brand cannot be drawn from that one sample.
Few of the Global Window Films were acceptable because the midpoints of the cutoff curves for most of these films were much too short in wavelength. The films also had uneven transmission in the visible range, although visually
the films did not appear as highly colored as the colorimetric data would indicate. Only the darkest tinted films were found to reject an adequate amount of UV light. These findings
correlated with the findings of the previous study (6).
The tinted HanitaTek films did not perform well according to the criteria used in this study. In particular, the Optitune and Silver lines are highly mirrored and appear slightly blue. While non-neutral color is not necessarily a failing for these films, which are marketed for their aesthetics as well as their utility, it does make them unsuitable for use in a museum setting. UV rejection was also variable.
Of the less widely distributed films, the Artscape Energy Film, a do-it-yourself adhesive-free film, is clearly unsuitable for museum use. The V-Kool films, which are marketed primarily as IR-blocking rather than UV-blocking, perform acceptably but have too much of a green tint.