![]() The user control experience produced by conventional LED dimming is jerky, unintuitive, and unsettling. Further small turns on the dial at below 20% of full power can produce abrupt changes in brightness, followed by sudden darkness at the lowest dimming level. This often gives the user the impression that the dimmer is broken or malfunctioning. Many dimming controls fail to take this non-linear behavior into account, so when a user turns a dial or moves a slider to request half-brightness, the dimmer cuts the power in half – and the user sees no change (see Figure 2). At a measured light output of 1%, the eye fools the brain into thinking that the light is only dimmed to 10%. As Figure 1 shows, reducing the measured light output of an LED luminaire to 10% of full intensity is perceived as around one-third of full brightness. The human eye becomes more sensitive to changes in light intensity the dimmer the light becomes. To the human eye, however, this 50% fall in measured light intensity is almost imperceptible. Cutting the current to an LED by 50% cuts the light output from the LED by 50% - a linear response to a control input. Unfortunately, this alignment is rarely achieved in large-scale LED lighting installations, for two reasons.įirst, LED light sources do not behave as the eye does. To achieve either of these effects, there must be correct alignment between technology – that is, the controlled flow of electrical current to a light source – and the human eye's response to changes in light intensity and color. To fill a space with the right amount of light for the activity taking place in it– for instance in a theatre's auditorium, where full brightness is needed before and after a performance, but very dim lighting is required during the performance To create a cozy, snug ambience – perfect for diners on a romantic night out in a restaurant, or perhaps for the living room lighting at home where a family spends the evenings When a lighting designer or a specifier of a new lighting scheme requests dimming capability, they commonly want to achieve one of two effects: ![]() ![]() The Human Eye: A Non-Linear Photometric Sensing Device It's critical to understand why we see poor LED dimming applications and how to specify dimming so that it meets expectations across an entire lighting installation. Inconsistency in the color of dimmed light from one luminaire compared to its neighbor is equally unmistakable. Moreover, the difference between smooth, intuitive dimming and jerky, unpredictable dimming is instantly apparent to lighting professionals and end-users. But with modern LED lighting systems, the function is more complex and it's surprisingly common to achieve poor dimming performance. Prior to LED lighting, it might have been safe to assume that all dimming schemes functioned in a similar and fairly consistently way. Making it easy to take it for granted.įrom a building operator's point of view, dimming capability is now a standard, functional requirement that's more technically demanding and requires careful specification and implementation. We've built dimming capabilities into lighting systems for decades. Dimming-and the regulatory user controls such as rotary switches or sliders-is a familiar function.
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