Factors Impacting Light Perception
How humans experience light has been the focus of numerous studies. Lighting has the potential to make a street feel safe or ominous, can make a retail space feel cozy or cold, and can make conference attendants feel energized or drained. Understanding the interrelatedness of lighting composition and human perception is therefore extremely important in order to design effectively-lit environments.
Explaining the relationship between lighting design and how it impacts human psychology starts by appreciating how our eyes work. When illumination is bright, our pupils contract, allowing us to see greater detail, color, and depth. Conversely, in low light, our pupils dilate to allow in more light. Our eyes are composed of rods and cones. While rods function in dim or scotopic conditions, cones provide color vision and fine detail in bright or photopic light.
There are many other factors that impact how we perceive light. Human vision is affected by:
- Color
- Contrast
- Glare
- Motion
- Air quality
- Reflections
- Light intensity
- Light distribution
Measuring Lumens with Human Pupils in Mind
Traditionally, interior lighting designs were calibrated based on the photopic or bright light response of our eyes. However, recent studies have suggested that scotopic vision must be taken into consideration because of its impact on pupil size. After all, by simply measuring lumens, you cannot fully predict how well people will be able to see. For instance, with low-sodium lamps which produce only high-lumen yellow and gray colored light, it is difficult to make out detail. Lighting with greater spectral output but fewer lumens, on the other hand, may actually improve visibility.
As a result, many researchers today are looking at how the photopic/scotopic (P/S) ratio of lamps impacts human vision. They have developed a figure that expresses the effective lumens perceived by the eye based on pupil size (see Table 1). This conversion factor applies the P/S ratio to lumen output of a given light source. When calculated, the conversion factor for light sources such as low-pressure sodium lamps show that most of the light output is lost. High-quality fluorescent lamps, on the other hand, gain a substantial amount of visibility by comparison when this conversion factor is applied.
Evolving Lighting Trends
With these changes in how we understand pupil lumens, lighting designs are being transformed as well. For example, in the past high-pressure sodium lamps were common for street lighting, but their yellowish light obscures detail. Instead, lighting options that output white light in low-light conditions are now gaining popularity. White light with greater color rendering offers many advantages for a variety of settings:
- It is more welcoming and enticing in retail settings.
- It makes it easier to see pedestrians, objects, or animals on roadways at night.
- It is common in downtown settings as it offers greater safety and aesthetic appeal.
- It provides illumination that encourages academic success in educational settings.
- It impacts human productivity, making a noticeable impact on efficiency for commercial businesses.
Though current building standards have yet to catch up to the trends brought on by our understanding of pupil lumens, no doubt they will do so in the coming years. In the meantime, those businesses that understand the importance of choosing lighting designs based on pupil lumens and color rendering will attain substantial visual performance advantages over their competitors.
