Outdoor Security Lighting - High-intensity Discharge Lights
Many lamp varieties are used in outdoor security lighting. Which lamps you decide to use is going to depend, at least in part, on where you want the lights situated and how brightly you want the area lit. Other factors that will affect your decision are desired light intensity, color rendering index (CRI), correlated color temperature (CCT), lifespan, and energy efficiency.
Color rendering index refers to a lamp's ability to faithfully render colors, as compared with a natural or optimal light source. Daylight is the typical benchmark. The higher a light registers on this quantitative index, the more capable it is of faithfully producing colors.
CRI does not describe the visible color of the lamp. That is the job of correlated color temperature.
Correlated color temperature refers to the specific temperature a theoretical light source would need to be heated to achieve a light that produces a color of a reference source of light. It is measured in degrees kelvin (K). Kelvin is a unit of absolute temperature; a topic beyond the scope of this article.
CCT essentially measures the overall warmth or coolness of a lamp's appearance. Lower temperatures refer to warmer light sources, and vice versa. Colors below 3200 K are considered warm (red/yellow/gold), while colors above 4000 K are generally considered cool (blue hue).
Lamps can be broken down into two main types: high Intensity discharge (HID) and halogen.
Here's a brief description for HID:
HID lamps - have the longest lifespan and highest efficacy of any light source. Efficacy refers to the amount of light produced as measured against the amount of energy expended in the process. Simply put, this means they radiate more light per watt of electricity consumed because a higher proportion of their radiation is light, as opposed to heat.
HID lamps manufacture intense light using an electrical arc. Electrical arc, in this instance, refers to a process that involves a quick breakdown of the resistance of gas contained within the bulb's quartz or alumina arc tube. This arc tube contains both gas and metal salts and the breakdown occurs between 2 electrodes within the arc tube. Gas is used to provide the initial spark.
Once sparked, the electrical arc gradually heats the metal salts contained within the arc tube. The heating of these metal salts forms into a continuous plasma discharge, which greatly adds to the light's intensity, while at the same time reducing its energy consumption.
HID lights require a ballast: a device used to ignite and harness the current flow within the arc tube. More specifically, it converts existing voltage into a higher operating voltage in order to spark the gas and metal salts into producing light. Once ignited, it can sometimes takes 5 minutes or more for the ballast to fully establish the electrical arc. This means it could take more than 5 minutes for these lights to produce light once activated.
And the upshot of all this is that while HID lights are an excellent source of continual light, they are much less so when it comes to motion sensor outdoor lighting, which requires a lamp to immediately produce light. HID lights are best applied when incorporated with other outdoor security lighting fixtures capable of instant activation.
HID Light Types
The type of gas used within the tube determines what kind of HID lamp you are working with. Metal halide, neon, xenon, sodium, mercury, argon, and krypton are all HID lamp varieties.
Here's a brief overview of a few of the main types of HID lights:
Mercury vapor lamps - are the first generation HID lamp. Of all HID lights, mercury vapor lamps are the least efficient. Original models produced a blue/green light, but more recent models have toned down the blue/green effect by adding a phosphor coating to the bulbs. The coating improves the CRI (color rendering index) and balances the light spectrum, which gives the light a white appearance. Mercury vapor lights typically have an outer bulb that contains the inner arc tube. The arc tube is comprised of quartz and is filled with mercury and argon gas.
Metal halide and sodium vapor lamps are increasingly replacing mercury vapor lamps, both of which are more efficient and have better color rendition than mercury vapor. Perhaps the reason mercury vapor lamps have not disappeared entirely is because of how long the bulbs last. The average HID bulb life is 24,000 hours or more.
Metal halide lamps - emit an extremely bright light and provide the best color rendition of all HID lamps. These lights are most commonly used in construction sites, commercial buildings, parking lots, sporting arenas, and other areas where safety and security is the primary goal.
Metal halide lamps have arc tubes that contain mercury, argon and metal halide gas. Metal halide gas facilitates greater light intensity, better energy consumption, and better CTR and CCT than what mercury vapors lamps are able to achieve.
Sodium vapor lamps - come in 2 varieties: low pressure and high pressure.
Low pressure sodium vapor lamps have the highest efficacy of all HID lights. The gases in the arc tube of these lamps are solid sodium, argon, and neon. The lamp emits a faint pink/red light as it begins to heat the solid sodium. As the sodium vaporizes, the lights display the red/yellow glow they are known for.
A downside of these lights is they produce a monochromatic light. This means objects all appear the same shade of color. These lamps are used in instances where color is not a primary concern, which makes them useful for such things as highway, parking lot and security lighting.
High pressure sodium lamps - as the name implies, work under high pressure and high temperature. The result is a more visually appealing light, but this is accomplished at the expense of energy efficiency.