Lighting Principles and Terms
To choose the best energy-efficient lighting options for your home, you should understand basic lighting principles and terms.

Light Quantity

Illumination
The distribution of light on a horizontal surface. The purpose of all lighting is to produce illumination.

Lumen
A measurement of light emitted by a lamp. As reference, a 100-watt incandescent lamp emits about 1750 lumens.

Footcandle
A measurement of the intensity of illumination. A footcandle is the illumination produced by one lumen distributed over a 1-square-foot area. For most home and office work, 30–50 footcandles of illumination is sufficient. For detailed work, 200 footcandles of illumination or more allows more accuracy and less eyestrain. For simply finding one's way around at night, 5–20 footcandles may be sufficient.

Energy Consumption

Efficacy
The ratio of light produced to energy consumed. It's measured as the number of lumens produced divided by the rate of electricity consumption (lumens per watt).

Light Quality

Color temperature
The color of the light source. By convention, yellow-red colors (like the flames of a fire) are considered warm, and blue-green colors (like light from an overcast sky) are considered cool. Color temperature is measured in Kelvin (K) temperature. Confusingly, higher Kelvin temperatures (3600–5500 K) are what we consider cool and lower color temperatures (2700–3000 K) are considered warm. Cool light is preferred for visual tasks because it produces higher contrast than warm light. Warm light is preferred for living spaces because it is more flattering to skin tones and clothing. A color temperature of 2700–3600 K is generally recommended for most indoor general and task lighting applications.

Color rendition
How colors appear when illuminated by a light source. Color rendition is generally considered to be a more important lighting quality than color temperature. Most objects are not a single color, but a combination of many colors. Light sources that are deficient in certain colors may change the apparent color of an object. The Color Rendition Index (CRI) is a 1–100 scale that measures a light source's ability to render colors the same way sunlight does. The top value of the CRI scale (100) is based on illumination by a 100-watt incandescent light bulb. A light source with a CRI of 80 or higher is considered acceptable for most indoor residential applications.

Glare
The excessive brightness from a direct light source that makes it difficult to see what one wishes to see. A bright object in front of a dark background usually will cause glare. Bright lights reflecting off a television or computer screen or even a printed page produces glare. Intense light sources—such as bright incandescent lamps—are likely to produce more direct glare than large fluorescent lamps. However, glare is primarily the result of relative placement of light sources and the objects being viewed.

Lighting Uses
Ambient lighting
Provides general illumination indoors for daily activities, and outdoors for safety and security.

Task lighting
Facilitates particular tasks that require more light than is needed for general illumination, such as under-counter kitchen lights, table lamps, or bathroom mirror lights.

Accent lighting
Draws attention to special features or enhances the aesthetic qualities of an indoor or outdoor environment.

With an average life span of 100,000-plus hours (11 years), IQ LEDs operate reliably year after year and are virtually maintenance free.

Outdoor Solar Lighting
Outdoor solar lights are easy to install and virtually maintenance free. Best of all, they provide free electricity.

Outdoor solar lighting systems use solar cells, which convert sunlight into electricity. The electricity is stored in batteries for use at night. Manufacturers most commonly use nickel cadmium, sealed lead acid, and lead acid batteries.

Outdoor solar lighting systems will work in most areas of the United States. However, it is important to consider geographic and site specific variables when choosing a product. A solar lighting system will work well only as long as the solar cells receive the manufacturer's recommended hours of sunlight.

The "nightly run time" listings on most "off-the-shelf" products are based on specific sunlight conditions. Outdoor solar lights located in places that receive less sunlight than the solar cells need will operate for fewer hours per night than expected. Nightly run times may also vary depending on how clear the sky is on any given day. Operating times in the winter months may vary as much as 30%–50%. Unless the solar lighting system has been sized specifically for winter operation, it will not operate for the specified number of hours per night in a given location. Shading of the solar cells by landscape features (vegetation, buildings, etc) will also impact battery charging and performance. Watch for bird droppings, too. Insufficient battery charging will not only affect performance, it also may reduce the life of the battery.

Some solar lighting systems are self-contained units. You only need to place the lights in a sunny location. Others have the lights separate from a solar cell panel. Only the panel needs to be placed in a sunny location. Units vary in size from small eight-inch, red-glowing pathway markers to pole-mounted patio and high-beam security lights.

Before you buy an outdoor solar lighting system, check with the manufacturer to see if replacement bulbs or batteries are available. Some units do not provide replacement options.

Home outdoor solar lighting systems are often available in hardware, lighting, and discount stores as well as through environmentally oriented mail order companies.

Metal Halide Lamps
Metal halide lamps produce a bright, white light with the best color rendition among high-intensity lighting types. They are used to light large indoor areas, such as gymnasiums and sports arenas, and outdoor areas, such as car lots.
Metal halide lamps are similar in construction and appearance to mercury vapor lamps. The addition of metal halide gases to mercury gas within the lamp results in higher light output, more lumens per watt, and better color rendition than from mercury gas alone.
Metal halide lamps have shorter lifetimes (5,000–20,000 hours) compared to both mercury vapor and high-pressure sodium lamps.

High-Intensity Discharge Lighting

In a high-intensity discharge lamp, electricity arcs between two electrodes, creating an intensely bright light. Mercury, sodium, or metal halide gases act as the conductor.
High-intensity discharge (HID) lamps provide the highest efficacy and longest service life of any lighting type. They can save 75%–90% of lighting energy when they replace incandescent lamps.
HID lamps use an electric arc to produce intense light. Like fluorescent lamps, they require ballasts. They also take up to ten minutes to produce light when first turned on, because the ballast needs time to establish the electric arc.
Because of the intense light they produce at a high efficacy, HID lamps are commonly used for outdoor lighting and in large indoor arenas. Since the lamps take awhile to establish, they are most suitable for applications where they stay on for hours at a time. They are not suitable for use with motion detectors.
Types of High-Intensity Discharge Lamps
These are the three most common types of HID lamps:
• Mercury vapor lamps
• Metal halide lamps
• High-pressure sodium lamps.
You can use the chart below to compare these types of lamps. If you don't already, it helps to understand basic lighting principles and terms before making.

https://www.eere.energy.gov/features/dept_energy.html

Ratatouille and Department of Energy TV Spot (Text Version)
Below is a text version of the Ratatouille and Department of Energy TV spot on energy efficiency.

"Rat!" (An animated chef yells and runs out of the kitchen in a panic. A rat holding a chunk of cheese over his head runs across the kitchen counter, scared and knocking over dishes while the kitchen staff chases him.)

(voiceover)
When it comes to our everyday activities, some of us use more energy than others.

(A blindfolded young chef works in front of a stove, flipping a pancake. The rat sits on his head and pulls on his hair, directing the chef's actions like a marionette puppet. The pancake flies out the window.)

But we can all be more energy efficient.
(A rat walks out in front of blank screen, kicking around an incandescent light bulb like a soccer ball.)

You could change from regular light bulbs to ENERGY STAR compact fluorescents.

(The rat flips up the light bulb off screen, and then catches a compact fluorescent bulb and winks.)

Just imagine how much energy we'd save if this whole city changed bulbs. (The rat looks out over a panoramic view of Paris.)

(Chef exclaims) "Exactly!"

Brought to you by Disney Pixar's Ratatouille, and the Department of Energy.

(A menu opens showing the words "From Disney Pixar Ratatouille" and the page turns to reveal the U.S. Department of Energy logo.)

To read up on more tips...

(A rat opens a cookbook, while another asks him,)

"You...read?"

(The first rat responds,) "Well, not excessively."

Source information https://www.eere.energy.gov/ U.S. Department of Energy