Kelvin (K)

Color Rendering Index (CRI)



Foot Candle

What is Kelvin (K)?

Kelvin (K) is used in lighting to measure the color temperature of a particular light bulb.  The higher the Kelvin rating, the whiter the lighting will be.

Color temperatures higher than 3500K are typically used for commercial and hospital applications, but task lighting may be useful at 4000K and above.

What K temperature do I need?  Use the Kelvin temperature scale below to determine the appropriate hue certain bulbs provide.


  • Less than 2000K: gives off a dim glow of light; similar to what you might find from candlelight; best for low light areas where ambient illumination is welcomed.

  • 2000K-3000K:  gives off a soft white glow, often yellow in appearance; best for living rooms, dining rooms, bedrooms and outdoor spaces

  • 3100K-4500K:  gives off a bright amount of white light; best for kitchens, offices, work spaces and vanities where task lighting is needed

  • 4600K-6500K:  gives off a bright amount of blue-white light; similar to that of daylight; best for display areas and work environments where very bright illumination is needed

  • 6500K and up:  gives off a bright bluish hue of light, often found in commercial locations; best for bright task lighting



What is Color Rendering Index (CRI)?

The measurement of light in relation to how it affects the appearance of color. The CRI ranges from 0 -100, with 0 being monochromatic and 100 being the full spectrum. The higher the CRI, the better the visual perception of color.  Most LED bulbs score an 80 – 90 on the chart.


Lumens, Illuminance, Foot Candles

In defining how bright something is, we have three things to consider:

1. How bright it is at the source

2.  How bright is that light

3.  How much light is falling on something a certain distance away from the light


What is a Lumen?

Lumens measure light output, whereas watts measure consumed energy use.  The brightness, or lumen levels, vary widely, so use this scale:

To replace a 100 watt incandescent bulb, look for a bulb that gives you about 1600 lumens

To replace a 75 watt incandescent bulb, look for a bulb that gives you about 1100 lumens

To replace a 60 watt incandescent bulb, look for a bulb that gives you about 800 lumens

To replace a 40 watt incandescent bulb, look for a bulb that gives you about 450 lumens

Here are some guidelines used in comparing lumens









What is Lux?

Lux is the measurement of actual light available at a given distance.  A lux equals one lumen incident per square meter of illuminated surface area.  Lux is an abbreviation for Lumens per square meter.  Foot candles equal the amount of Lumens per square feet of area.  One candlepower equivalent equals 12.57 lumens.  To determine LED equivalents, learn how many lumens are produced by the LED, then divide that value by 12.57 and that gives the candlepower of the LED.  

What is a Foot Candle?

A foot candle (lumens per square feet) is how bright the light is one foot away from the source.  A lumen is a way of measuring how much light gets to what you want to light.  A lumen is equal to one foot candle falling on one square foot of area.

How to convert foot candles to lumens and watts:

To calculate lumens from foot candles:  Lumens = Foot Candles x 10.76

To calculate watts from foot candles:  Lumens x 0.001496

To calculate the number of watts from foot candles:  Watts = Foot Candles x 0.01609696

















Current Light Bulb Options

There are three alternatives to recreate the incandescent light in an energy-efficient way:  Incandescent Halogen, Compact Fluorescent and LED.

Incandescent Halogen

Efficiency:  At least 25% more efficient than standard incandescent

Dimmable:  Fully dimmable, just like standard incandescent

Light Appearance:  Bright white light and good color rendering

Average Light:  1,000 hours (standard medium base)

Fluorescent and Compact Fluorescent

Efficiency:  About 75% more efficient than standard incandescent

Dimmable:  Dimmable options

Light Appearance:  Wide variety of light colors and improved color rendering

Average Light:  8,000 hours (standard medium base)


Efficiency:  At least 75% more efficient than standard incandescent

Dimmable:  Dimmable options and LED-compatible dimmers available

Light Appearance:  Wide variety of light colors and high color rendering

Average Light:  25,000+ hours (standard medium base)

kWh Meter

kWh meter is the electric meter that measures the amount of electrical energy in kWh that is consumed.  The kWh meter has a counter display that counts units of kilowatt-hour (kWh).  The energy consumption is calculated by the counter's reading in a specified period.  The cost of an electricity bill is calculated by multiplying the number of kWh that were consumed by the cost of 1kWh.


Power Consumption of Some Electrical Components




LED Systems Cost Too Much

Fact:  With zero $$$ invested, operational and maintenance savings make it possible to participate in our long-term energy-saving program

LED Light Quality is Poor

Fact:  Most office, retail, educational, medical and residential spaces require a minimum CRI of 70 - 90.  Many white-light LED lighting fixtures available today achieve CRIs of 80 or better.

LEDs Generate No Heat

Fact:  Because LEDs produce no infrared energy, the beam of light from an LED source is cool.  The waste heat produced within the LED itself is during the conversion of electricity into light.  This waste heat is properly removed through carefully designed and engineered heat sinks that draw heat away from the LEDs and dissipate it into the air surrounding the fixture housing.

LEDs Last Forever

Fact:  With proper thermal design, LEDs can achieve an average of 50,000 hours of life while maintain 70% of original light output.  LEDs are designed to provide an average of 10 years of maintenance-free service with a 5 year bulb warranty.

LED Prices Will Go Down, So It Pays To Wait

Fact:  Waiting for LED fixture prices to drop will cost you money.  The energy savings from upgrading a facility's lighting to LEDs far exceeds any incremental price declines in LED-based fixtures. A quick glimpse at a typical facility's operating budget shows that lighting is one of the largest energy loads. By reducing the energy usage 50% to 90% (depending on the application and manufacturer), LEDs pay back in energy savings much more than could ever be accrued through incremental LED price declines.  Energy's upward price trend makes waiting even more costly. Using the same $0.10/kWh rate, for example, a single 6-lamp T8 fixture typically consumes $174 in lighting-related energy costs per year, while an LED fixture consumes just $27. This results in a net savings of $147 per year (not including the additional daylight harvesting, maintenance, and/or refrigeration savings associated with LEDs), meaning the cost of an LED fixture would have to drop dramatically in a single year to make waiting worthwhile.


Incandescent Bulbs Are Going Away

Fact:  Federal government changes are requiring incandescent bulbs become more efficient.  Traditional incandescent bulbs consist of 90% wasted energy in the form of heat, while only 10% is used for light production.