Understanding Intelligent Lighting Design, Part 1
Light Emitting Diodes
Light Emitting Diodes have been in use for several decades, but they are just now beginning to live up to their lighting system potential. From MR16 bulbs suitable for home lighting to powerful PAR floodlights and LED grow lights, LEDs enable a nearly infinite amount of variety and specialization. As LED lights replace their more traditional cousins in the consumer and industrial lighting markets, LED product developers face an array of challenges. The capability to create intelligent lighting fixtures, complete with sensors and dimmers, requires a shift in the language used to describe LED lighting. Much more is required of lighting designers than an understanding of lux and colour needs. Developers in the expanding field of Led lighting technology sometimes struggle to integrate intelligence features into their designs, and to describe these advances to vendors and potential business partners. A basic understanding of the fundamentals of intelligent LED lighting design will help developers and vendors communicate more clearly regarding future projects.
Dimming Though it seems simple enough, the question of whether dimming is a necessary design feature can be very complicated. If the answer is “yes,” several factors come into play, each of which presents unique challenges.
Input voltage Many fixtures for interior lighting, such as MR16 bulbs, are designed for low voltage and have 12 CAV (Voltage Alternating Current) or 24 VAC inputs. This makes it challenging to design a driver that works with most TRIAC (Triode for Alternating Current) dimmers already in use. A few companies have or are in the process of developing drivers with this capability. Options for dimming higher voltage fixtures are more abundant. At the top of the range are a few 277V dimmers for high-bay lighting.
Dimming system The next challenge to consider is dimming control. TRIAC design did not take LED lighting into account and a given AC/DC LED driver might not even work with about half of the usual TRIAC dimmers. Also, drivers sometimes can’t interpret the high and low ends of the TRIAC, severely restricting the effective dimming range, especially on the low-voltage end. Since typical AC/DC drivers are not designed for microcontrollers with a 5V input rail, AC power management becomes necessary when a microcontroller is used for dimming control. Additionally, an input signal is needed to regulate output dimming waveform adjustment. All of this may require integrating a communication network into the light fixture, to relay dimming information.
Dimming Performance Dimming circuits are not all the same, introducing the question of dimming quality. Typically, a PWM (pulse-width modulation) signal is used to effect dimming. PWM is a digital waveform that modifies the amount of power delivered based on the PWM’s duty cycle. EMI noise (Electromagnetic Interference) sometimes results, causing the LED light to flicker. Thus, it is necessary for lighting developers to seek out low-noise solutions, such as drivers that regulate the PWM signal on a semi-random basis. Digital outputs can also affect how smoothly the dimmer works. For instance, there are only 256 steps possible when dimming a series of while LED bulbs using an 8-bit PWM. The user can see these dimming steps, especially at the dimmer’s low end. A 16-bit PWM allows 65,000+ dimming steps, for smoother dimming performance.