When it comes to lighting design, good design starts with identifying the needs of the space. From there, you can decide what surfaces you will be lighting and at what intensity. From there you can begin picking out your equipment. The average lighting system includes a light source, ballast or driver, lighting fixture, and controls. Want to know al about lighting design 101? We’re here to help you out. Read on to find out more!
The light source is at the heart of the system with other components merely supporting it. The fixture directs intensity of light, ballast starts the lamp and regulates its operation, etc. Families have tons of choices for lighting incandescent, halogen, fluorescent, solid-state lighting (LED), or high-intensity discharge. Picking the right source will be important to your project’s success.
Compare the distribution of light in candelas, how long it lasts, how many lumens it produces, how much wattage and power the system requires, how efficient it is, its color appearance and tone (kelvins), and how well it renders colors on the CRI (color rendering index).
Figure out what distribution you want when starting out. Most sources have a size and shape that affects how it will illuminate things. You can use point sources in small lamps with a clear outer bulb or bare filament to produce shadows and light contrast. Linear sources will soften shadows and diffuse output from the lamp’s surface, while area sources are large surfaces that diffuse light.
The service life of lamps is expressed in a rated burn time, or operating hours. The catalog from the manufacturer will have the rated lamp service life. It’s not a precise prediction, but an expectation of field life. HID and fluorescent lamps have a predictable lamp rate of failure that is 3 hours per start for fluorescent and 10 per start when it comes to HID. Basically, if the cycle is short, the lamp life will be too.
On the other hand, some lamps really do last quite a long time. Extended life fluorescent lamps can get a rated life of 55,000 hours and 12 hours per start. Your ballasting and controls will also affect the life, with instant-start operation having a shorter life while programmed-start operations will boost it. Also be sure to check what the source’s failure mode is, which may include color shift at end of life, inefficiency, and lamp cycling.
The light output can also be found in the catalog provided by the manufacturer. HID and fluorescent lights have affected light output due to their ballasts.As lamps age, they do tend to produce less light. This is thanks to a process known as lamp lumen depreciation, or LLD. All lamps experience this in different ways, which you can find according to their lumen maintenance curve. Take the LLD into your consideration when calculating lighting design for best results.
Lamp input wattage can be found in catalogs. It will tell you how much power the lamp requires in order to operate. Rated wattage for lamp-ballast combination can be found in the catalog and will give you the greater practical value.
Relative efficiency is compared using efficacy. This expresses the ratio of light output/unit of electrical input (LPW). Efficacy goes down over time while output is affected by LLD, but wattage stays the same. Efficacy has more value in decision making than initial efficacy. Efficacy may also decline over the dimming range of a lamp, with LEDs as the exception. It’s really used for comparing light sources that are similar in light design.
Lamps all produce light that have a certain color appearance. This will affect objects and how they appear when the light hits them. It also influences how the color of the lamp itself appears. The temperature indicates the color experience and the light it will put out. Lights lower than 4,000 K are cool and blue-white, neutral are 3,000 to 4,000 K and appear white, and warm is 3,000 K. Temperature will describe its color but will not define how objects appear in color when they are lit, and lamps can render colors differently even though they have the same color temperature.
The CRI is used to address this. In many applications, a higher CRI is ideal. 80-100 is considered fantastic for naturally rendered colors. You can use a CRI of 90 and up for color-critical applications. However, ultimately the most accurate result of their color characteristics will come from its spectral power distribution curve (consult the manufacturer). Asking these questions will allow you to predict light and install designs that illuminate the world around them just like you want them to.