Glare & Contrast

Introduction

Sunlight is one of the most sought after components in a space, and codes are written to require access is provided to the resource. However, sometimes there is too much of a good thing. Too much sunlight in certain conditions can cause glare and contrast issues. Understanding the general circumstances that create these problems is imperative to try and prevent them.

While sunlight is the way we introduce this concept, this is also a major concern with interior spaces and artificial lighting. Most important is to understand the activities taking place in your space, as well as the factors that might affect it. While the principles are the same… glare from the sun in a baseball stadium is a different issue to solve than glare in an office building from overhead light.

There Are Two Types of Glare

Direct Glare

Direct glare occurs when a light source in the field of vision causes any amount of discomfort and interferes with the task at hand. Not all sources of light will cause discomfort; there are many factors to the discomfort such as brightness, position, background illumination, etc.

• Visual Comfort Probability (VCP): Is a metric used in evaluating the problem of direct glare. VCP is the percentage of normal observers who may be expected to experience visual comfort in a particular environment with a particular lighting situation.

  • Many manufacturers include VCP information in their specifications, published under certain condition criteria.

• For most situations, the critical zone for direct glare is in the area above a 45 degree angle from the light source. This can be avoided or eliminated by using luminaires that have a shroud and cutoff angle for the light of 45 degrees or more.