It is known, that materials based on ZnS don't alter their luminance in a great range with the charging conditions. It is approximately between 2 and 3 mcd/m2 after 60 minutes discharge. So, the change in the width of the guidance line is insignificant.
On the other hand, the luminance of products based on strontiumaluminate depends strongly on the charging conditions. Based on measurement to the charging behaviour done by us, picture 4 shows the width of the guidance lines for the three earlier mentioned formulas in dependence from the illuminance on the product.
Picture 4 : Width of a guidance line in dependence of the illuminance on the photo-luminescent product.
The graph is valid for EverGlow HI® 150 and charging by an cool white fluorescent lamp for a long charging time.
The widths were calculated for the three formulas of table 1.
The graph is valid for EverGlow HI® 150 and very long charging time at cool white fluorescent lamp. It can be seen, that the width of the guidance line changes for a maximum of 1 cm between 10 and 1000 lx (worst case; depends on the formula). It is also much smaller than the up to know prescribed 10 cm.
So it can be said, that
1. also in the practical use the width of the guidance line can be decreased and
2. the width of the guidance line must be calculated not on the luminance values according to DIN 67510-1, but on the values the photoluminescent material reaches on the place of application.
Summary
Based on the presented data it can be summarised, that
1. it is possible to alter the width of the guidance line according to the luminance of the photoluminescent material,
2. it is not useful to set only one width at all,
3. to calculate the width of the guidance line, the circumstances at the place of application must be considered,
4. the different formulas result in very different widths of the guidance line and so,
5. based on the available material, it is impossible to definitively recommend one of the formulas.
Literature
[6] Webber, G. M. B. and Shipp, M. P. ,,Review of Emergency Lighting and Way-guidance Systems for Offshore Structures"
Health and Safety Executive 1996
[7] Willing, A. ,,A Practice Curve of Visual Acuity"
Document ISO/TC 145/SC 2/WG 3 N36 September 1996 (unpublished)
[8] Willing, A. ,,Erkennungsweite von Zeichen und Piktogrammen" Licht 10/97, S, 884 - 891
[9] Blackwell, H. R. ,,Contrast Thresholds of the human eye" Journal of the Optical Society of America, Volume 36, Number 11, 1946
