Introduction

A new area for the fogging test within the automobile industry is HID (High Intensity Discharge) headlight components. HID lights operate at high temperatures in a micro-environment typically comprised of a polymer reflector and lense and the glass HID bulb. The outgassed SVOCs re-condense on all surfaces of the bulb, reflector and lens when the HID light is turned off. The resultant film reduces light transmittal from all components and refracts or scatters the light in undesirable directions, potentially reducing night time visibility for the driver.

Methods

Fogging Behavior DIN 75201 Reflectometric method, photometric method, fogging method, gloss method

According to this method, a prepared sample is placed in a beaker that is then covered with a glass plate. The plate’s Reflective Index has been measured and recorded using a handheld reflectometer. For a period of three hours the sample is heated to 100°C, while the glass plate is cooled to 21°C. The heat causes the sample to release SVOC gasses that condense on the cooled glass plate creating a “Fog” (F). The Reflective Index of the fogged glass is measured and recorded.

Fogging value (Fv) is expressed as a percent of change in the 60° Reflective Index of a glass plate that has been fogged in accordance with the procedures (R1) to a clean glass plate (R2).

Fv = (R2 x 100)/R1

Where:

Fv = Fogging value

R1 = the mean initial reflective index of the glass plate with the fogging condensate

R2 = the mean initial reflective index of the glass plate

DIN specifies the maximum value for Fv in this test at 90%

fogging tester with these three test methods

Fogging Behavior DIN 75201 Gravimetric method

According to this method, a prepared sample is placed in a beaker that is then covered with an aluminium foil disk. The disk’s mass has been measured and recorded. For a period of sixteen hours the sample is heated to 100°C, while the aluminium foil disk is cooled to 21°C. The heat causes the sample to release SVOC gasses that condense on the cooled aluminium foil disk creating a “Fog” (F) that has a measurable mass (m). The amount of fogging condensate is determined by weighing the aluminium foil disk again after the test and subtracting the known mass of the same aluminium foil disk before fogging.

mF = m2 – m1

mF = the mass of the fog condensate collected during the test

m1 = the initial mass of the disc of aluminum foil (milligrams)

m2 = the mass of the disc of aluminum foil with the fogging condensate (milligrams)

This is the preferred method because the longer run time and simple measurements increase accuracy while minimizing errors inherent in the reflectometric method such as contaminated or damaged glass, using the incorrect side of the glass, or errors in measuring the reflective index