The Appearance of Haze

Haze can occur on most coated glass, both hard and soft coated. However, the effect will be more noticeable on some types of coated glass than on others. Haze gives the appearance of a fine, uniform, layer of dust deposited on the surface of the glass. The effect is more noticeable when the glass is viewed at an angle or under strong light. In situations where the glass is in partial shadow, the shaded area will be free of the effect giving a clean appearance in the shadow and a dusty appearance in the lit area. This contrast can be very noticeable. SGG EKO LOGIK hard coated low-E glass can manifest this effect. The reason for this is that the coating is not as smooth as the glass surface. This 'roughness' of the coating is not apparent to the human eye. However it can be felt and it is possible to identify the coated surface by running a hand over the surface to feel the resistance of the coated surface. This 'roughness' scatters a small proportion of the light striking the surface of the coated glass in much the same way as it would if there was a thin layer of dust on the glass, hence the reason for the visual similarity between the two. Manufacturers of low-E glass aim to limit this effect as far as is possible, but it cannot be totally negated. However, the effect does not appear to be as apparent on soft coated glass such as the SGG PLANITHERM family of low-E products. This is due to the higher levels of sophistication of the soft coat manufacturing process.

Extract from document supplied by Saint Gobain Glass UK Ltd.
Weeland Road, Eggborough,
East Riding of Yorkshire
DN14 0FD

Pilkington K Glass™ and the Appearance of Haze (Pilkington UK Technical Bulletin )

Haze is an optical phenomenon which makes the glass look like it is covered in a very fine, uniform, layer of dust when viewed from an oblique angle or viewed under strong light incident on the glass at an oblique angle. Pilkington K Glass™ can, under certain lighting conditions, display this phenomenon to a limited extent. The reason for this is that the Pilkington K Glass™ coating is not as smooth as the glass surface. While this is not obvious to the eye when examining the glass, some people who regularly handle Pilkington K Glass™ can tell which side the coating is on by the feel of it. The optical effect of the slightly rougher surface is to scatter a small proportion of the light incident on it (in exactly the same way as a thin layer of dust would, which is why it looks similar). With Pilkington K Glass™, the amount of scattered light is generally less than half of one percent of the light coming through the window, so under most viewing conditions it is not obvious. However, when incident sunlight is at an oblique angle and the view through the glass is of a shaded area, then the scattered light can become more visible, giving rise to the appearance of haze.

Most coated glasses are susceptible to the phenomenon of haze, to a greater or lesser extent and the amount of haze on Pilkington K Glass™ is limited as far as practicable.

Extract from document supplied by Pilkington UK Ltd.
Alexandra Business Park Prescot Road
St Helens, Merseyside
WA10 3TT