LED Spotlight Fading Potential
An ongoing issue in retail lighting is LED spotlights’ fading potential. For a retailer, it is undesirable if lighting fades the goods, rendering them worthless. Following the technological shift from metal-halide lamps to LEDs, it was assumed that fading could no longer occur. In fact, LEDs’ spectrum does not have any harmful UV radiation. However, the intense blue peak can fade colours. In high-end retail spaces, the introduction of LED technology has significantly raised illuminance levels in recent years. XAL carried out a continuous test to find out how soon colour damage occurs at an illuminance of 3000 lx.
Four 3000 K spotlights, VOGUE LED with Ra 96, VIVID LED with Ra 96, XPECTRUM full-spectrum LED with Ra 98 and metal-halide (HIT), shone on textiles for 24 hours for 8 weeks. During the weekly checks, hardly any colour change was noticeable. A comparison of the new fabric with the samples irradiated for 8 weeks showed colour loss.
After 1340 hours of illumination at 3000 lx, noticeable light damage is to be expected. Illumination duration and intensity determine the impact. Duration and intensity can be offset against each other. Half the duration allows twice the intensity. 1340 hours at 3000 lx correspond to 670 hours at 6000 lx, etc. HIT and XPECTRUM have minimally more fading than VIVID and VOGUE. VIVID and VOGUE are the two most common light colours in the textile trade. The difference between individual light colours is not particularly large. A textile retailer must ensure that no product is exposed to this long lighting period with high illuminance at the same time.
Assessment of fading potential
One question that has arisen is whether pre-assessment of light sources regarding their fading potential is possible. We have a fading effect curve for textiles from the Technical University of Berlin. This effect curve was transferred to the visible range from 380 nm to 780 nm. Evaluating a spectrum with effect curves is not new. Several effect curves already exist, the best known being that of the spectral sensitivity of human visual perception of light, the V λ curve. The spectrum consists of 400 intensity values, one value per wavelength. When evaluating the spectrum of a light source, each wavelength is multiplied by the corresponding value of the effect curve. If this is done with the fading-effect curve and then all 400 values are added up, then the result is a damage value. The higher this value, the higher the damage potential of the light source.
Fading potential at CRI 80
3000 K CRI 80 (Standard LED)
3500 K CRI 80 (Standard LED)
4000 K CRI 80 (Standard LED)
Fading potential at CRI 90
3000 K CRI 90 (Bridgelux Vero13)
3500 K CRI 90 (Bridgelux Vero13)
4000 K CRI 90 (Bridgelux Vero13)
Fading potential with XPECTRUM
3500 K CRI 98 XPECTRUM (Bridgelux Thrive)
4000 K CRI 98 XPECTRUM (Bridgelux Thrive)
Conclusion
When comparing different light sources, a relative statement can be made in advance as to which of the light sources of the same irradiance is more harmful. One can see very clearly that warmer light colours have a lower fading potential than colder light colours.
