Lighting Lesson Depth

When we are talking about the dimming range, two terms are involved, "measured brightness" and "perceived brightness" respectively.

Because pupils of eyes dilate or contract in response to light intensity.

There is a nonlinear relation between measured brightness and perceived brightness according to the lighting manual of Illuminating Engineering Society of North America (IESNA).

For instance, as shown in the chart, measured brightness is 20% (0.2) by use of illumination meter while perceived brightness of eyes is/äT= 0.227(about 25%). Hence, measured brightness is 10% while perceived brightness of eyes is 32%. There exists a gap of 22%.

Lighting eventually should be based on perception of eyes. It is recommended that the dimming curve used commonly is expected to be in line with the dimming curve of eyes. To authentically achieve 1% brightness of eye perception, brightness ought to be adjusted at 0.01% (measured brightness).

Brightness marked on the market is measured brightness and it can be adjusted at 10/0-100/0 if PWM is used (Each brand may be different), which can be reached at 0.01%-0.1% by leading dimming technology and meet the strict requirements of no flicker.

Since eyes are low brightness sensitive, when lights are on and start with pretty low brightness, they sense comfortably. Thus, when lighting environments do not require high brightness, just turn brightness down to be visible.

It is more energy-efficient to use depth dimming in the space with high power and multiple lights, or to turn brightness down with sensors or time and scene control.

More professional dimmable drivers are with lower dimming depth values, which are mostly applied in hotels, museums, theaters, etc. But also due to wide dimming ranges, meanwhile they can be applied in other more occasions, such as commercial space, office, home, etc.

 

Conclusion

In recent years, the concept of Human Centric lighting has been applied in lighting designs, solutions and lighting products, which not only require to meet basic illumination and brightness, but also create comfortable, healthy and efficient artificial lighting environments that are beneficial to people's physical and mental health in accordance with people's environments, brightness demands, physiological and psychological characteristics.

In order to enable artificial light to show like natural light, its color temperature and luminous flux must make changes as the environment and time change. Different from several static scenes switching to achieve dimming in the past, artificial light must meet requirements of "dynamic" dimming changes. Hence, dimmable drivers play a more important role than ever before. Since there is no similar standards in the lighting industry, the author uses four criteria -"flicker-free", "smooth", "precise" and "depth" dimming respectively to clearly explain and make them as reference standards for selecting high-quality dimming, which are indispensable for professional LED dimmable drivers. These four criteria make a good reference that help proprietors, lighting designers, lights manufacturers, engineers, integrators and other relevant persons evaluate, select and compare LED dimmable drivers.