In part 1 of our series we had a look at the different expressions used in the lighting industry and LED lighting in particular.
I this second part of the series we have a closer look at the topic “Controlling LEDs.” An article found on the web site of Lutron
Less than ten years ago, many people didn’t even know what an LED was. Today, LED are the new hot item on the shelves – and everyone wants to use them. Problem is – often, designers do not know how to control LEDs or they have had negative experiences working with them. We will provide a brief overview of what an LED is and how to use LEDs for general illumination applications, their advantages and limitations of doing so. We will also going into detail about why you should consider dimming LEDs and what questions need to be answered in order to dim LEDs properly to meet your expectations. All this with the overall to make you more comfortable with using LEDs on your projects.
So lets go back one step and start with the basics.
What is an LED?
A Light Emitting Diode (LED) is an electronic device that produces light when an electrical current is passed through it. The wavelength (or color) of light that is emitted is dependent on the materials from which the LED is made. LEDs are available in many colors, including red, blue, amber, green, and near-UV colors, with lumen outputs ranging from 10 lumens to 200 lumens or nowadays even higher under lab conditions
The LEDs used predominantly in general illumination applications are “Phosphor Converted Blue” LEDs, which are blue LEDs that have a layer of yellow phosphor placed over the LED. The phosphor absorbs some of the blue light, and emits yellow light. When the unabsorbed blue light mixes with the yellow light it creates what your eye perceives as “white” light.
LEDs in general illumination – Advantages and Limitations
• High Efficacy (Lumens per Watt): LED fixtures can achieve efficacies ranging from 25 LPW to over 100 LPW, compared to an incandescent efficacy of 5-10 LPW.
• Longevity: LEDs can achieve useful lifetimes from 25,000 hours to up to 100,000 hours, compared to ~1000 hours for an incandescent.
• LEDs do not contain hazardous materials as compared to mercury vapor in CFLi bulbs.
• Higher cost: High Brightness LEDs, necessary for general illumination, are expensive. LEDs also require electronic drivers to convert conventional AC voltage to discrete DC voltages for the LED arrays.
• Applications limited: Applications are still limited due to the relatively young technology and timeline for wide acceptance, LED-based lighting fixtures are not always available for every application or aesthetic requirement.
• Compatibility with Controls: Due to the wide range of LED-based lighting product types, not all LED lamps are dimmable, and the ones that can be dimmed may be limited in dimming performance and system compatibility.
Why Dim LEDs?
Similar to fluorescent, incandescent and other conventional light sources, dimming LEDs saves energy at a roughly 1:1 ratio. This means that if you dim LEDs down to 50% of their light output you will save nearly 50% of your energy usage. So not only do you save by using a more efficient source, you save even more energy by dimming LEDs.
Dimming LEDs also makes them run cooler, which should extend the life of the electronic components of the driver, as well as the phosphor on the LEDs. This will extend their life, doubling or tripling the LEDs lumen maintenance. Research is ongoing to better quantify the relationship of dimming LEDs and lifetime extension.
Dimming any lamp, be it incandescent, CFL or LED enhances ambiance, so whether you are in a restaurant, theater or presentation space, you can create the environment that the lighting designer intended.
Besides the above dimming offer many other benefits including:
• Space Flexibility: Dimming control systems provide for space flexibility so that what may be an office space today could easily be converted into a call center tomorrow, or a gymnasium can be used as a theater or cafeteria just by adjusting the control of your lighting. Your home and your workplace should be designed to complement your needs. As your needs change throughout the day, your lighting should adapt as well; bright to read a book, but dim for computer use. Whether you are at home or at work, lighting control can create a comfortable atmosphere to support your activities throughout the day.
• Enhanced Safety: Lighting controls can enhance the safety and security of your home. You can control both interior and exterior lights from the car as you approach your driveway to ensure optimal visibility and can even connect to security systems to turn on lights in case of an emergency
• Increased Productivity: Lighting control also increases productivity allowing the user to select the level he/she needs to reduce eye strain and fatigue so that they can work at peak performance for more of the day, or so students can concentrate better and learn more at home or at school.
What questions do you need to ask when trying to dim an LED product?
Before you commit yourself or your customer to investing in LED technology you need to understand its limitations, especially when it comes to dimming control compatibility. Many LED luminaire manufacturers are new to the lighting industry and are not familiar with the multitude of control types and the corresponding product design requirements that accompany them. This has resulted in “dimmable” products that do not work as claimed, that never turn off completely, or that flicker. These are major problems that need to be addressed so that consumers do not associate all LEDs with poor performance and become averse to using them. High-performing LED products do exist, but you need to ask the right questions to make sure you have chosen one of those products appropriately.
Answering the following five questions will allow you to align your expectations with the potential performance of your selected LED dimming system.
1. What type of LED product am I using: an LED lamp or LED fixture?
2. What is the dimming range of the product?
3. What is the dimming performance of the product?
4. What is the minimum or maximum number of fixtures/lamps that can be connected to one dimmer?
5. On what type of control does the LED product operate?
In part 3 of our series we will in detail look at the questions above and explain what they mean…