Colourfastness to light:
The colorfastness is being assessed by comparison of the colour change of the exposed portion to the masked control portion of the test specimen using gray scale or blue references used. There are varios types of colorfastness test are used to measure garments quality. Light fastness test is one of the very important test required for consumers.
Light fastness is the degree to which a colorant resists fading due to light exposure. Different dyes have different degrees of resistance to fading by light. All colorants have some susceptibility to light damage, simply because their colors are indications that they absorb the wave lengths that they do not reflect. Light is energy, and the energy that is absorbed by the colorant compounds degrade them or nearby molecules.
The resistance to degradation (or fading) of fabric dyes and prints due to light is therefore an important requirement of a garment because without such resistance, the garment may change colour and such colour may not be acceptable to the customer.
Retailers are also becoming more aware of issues concerning color fastness to light. Higher colour fastness is now being demanded for apparel that will be worn predominantly outdoors.
Now a days the criteria of light fastness is hence be coming a major concern amongst buyers and consequently with dyers.
Purposes:
The purpose of colour fastness to light test, is to determine how much colour will fade when exposed to artificial light (xenon arc) which is representative of natural daylight.
This test measures the resistance to fading of dyed textile when exposed to day light. Here it is common to carry out physical tests before and after exposure to determine the degree of degradation.
Apparatus:
Machine used: ATLAS ci3000+ Xenon fade-Ometer
Preparation of specimen:
1、Artificial light is generated by Xenon Arc Lamp, which has a life span of 2000 hours.
It has two layers, inner and outer layer.
2、Inner layer is made up of Borosilicate (for American buyer) and Quartz (for European buyer). It has a life span of 400 hours.
3、Outer layer is made up of sodalime which is known as fload glass. There are 6 fload glasses arranged in a circular position. Life span of each fload glass is 666 hours.
4、The top most layer is made by the sample holder. There are 29 sample holders, each having a holding capacity of 4 samples.
Procedure:
1、First the samples are conditioned to 65±2 RH humidity and 20±2°c temperature.
2、Then it is put inside the sample holder for certain time, humidity and temperature according to the customer demand.
3、The humidity is usually kept at 40±5 RH and 30°c temperature.
4、After the process assessment to color fastness is done.
Assessment of color fastness to light:
1、The assessment is carried out by assigning rating to standard blue wool fabric.
2、It has a range of (8-1), 8 means good and 1 means worst.
3、Usually fabric below is rejected.
