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Lumens and LED Brightness

How Bright are LEDs When Compared with Incandescent Bulbs.

The most often asked question from most of our prospective users is “How bright are the Power Failure lights?”, or “How many lumens do they provide?”.  These pages describe light levels, units of measurement, a comparison of light output between standard incandescent light nights and an LED based night light such as the PowerSURE® Power Failure Light.

LEDs and Lumens - Part 1


Part 1:

   Bulb Brightness in Lumens

   Light Measurement Units and Relationships

   Light Measurement Equivalents

   Units in LED specifications

Part 2:
   Steradians Explained
   Calculating Candelas and Lumens
   Lumen Calculator
   LED Radiation Diagrams

Part 3:
   Comparing real bulbs to LEDs
   Illuminating a room with an LED
   LED based power failure lights
   LED Watts and Light Bulb Watts - How to Compare)


LEDs are widely accepted as a low energy light source for illumination of living spaces and many questions have been raised by individuals attempting to understand how much light is produced by a High Brightness (HB) LED when compared to an incandescent light bulb. HB LEDs are characterized by luminous intensity, usually in millicandelas, candela, or Lumen (mcd, cd, lm) in an LED specification, while most incandescent bulbs are rated in watts and lumens. How can you compare them?

Bulb brightness in Lumens

  • A 100 watt Bulb is rated at approximately 1700 lumens
  • A 60 watt incandescent bulb is rated at approximately 800 lumens
  • A 40 watt bulb is rated at approximately 400 lumens
  • A 25 watt bulb is rated at approximately 180 lumens
  • A 4 watt night light bulb is rated at approximately 20 lumens

LED ratings of 25,000 mcd become conceptually difficult to understand when we are accustomed to light being expressed in terms of lumens. Published lumens represent the sum of all the light emitted by the bulb in all directions.

Light measurement basics

Both candela and candlepower correspond to the amount of light (i.e. the quantity of photons) produced by a standard light source. Originally, the standard light source was a real candle so it is also called candlepower. But like most measurement standards, it's now a theoretical construct having a specific wavelength of visible light at a specific power level. The good news is that the intensity of the standard candela is nearly identical to the original standard candle. All other quantitative measurements related to light are derived from the candela.

Candelas are a measure of the amount of light generated at a source. Lumens quantify how much total light flows away from the source. Foot-candles and LUX indicate how well the surface area of an object, wall or floor is illuminated at some distance away from the source (intensity of the light reflecting off objects like the floor, wall, or worksurface).

So what does this mean? If you have a light source of 1 candela, it's also 1 candlepower in intensity. If you measured the light on a 1 square foor surface, 1 foot away, it will have 1 foot-candle of illuminance over it's surface. In metric terms, if you measured the amount of light on a square meter that was 1 meter away, it will have 1 LUX of illuminance.So you could say that the light source is generating 1 Lumen in the direction of the 1 square meter that is 1 meter away. If the light source is in the middle of a sphere and generating light in all directions, you will find that the 1 cendella light source is generating 12.57 lumens as explained below.

Light Measurement Equivalents and Common Illumination Levels:

- 1 square meter (M2) = 10.7638 ft2
- 1 LUX is defined as 1 lumen/ M2 of a surface; thus 1 LUX= 0.0929 FC,
- 1 foot candle (FC) is 1 Lumen/ ft2 of a surface; thus 1 FC=10.7638 LUX
- There are 12.57 square meters on the surface of a 1 meter radius sphere.

In real life objects are illuminated and measured in LUX:

- Full Daylight is about 10,000 LUX (imagine 10,000 lumens each and every square meter!)
- Cloudy day is about 1,000 LUX
- A lighted parking lot at night is about 10 LUX (average)
- A full moon is about 0.1 LUX

OSHA Lighting Level Recommendations for Work Spaces:

- Public spaces with dark surroundings.................................30 LUX
- Simple orientation for short temporary visits........................50 LUX
- Working spaces where visual tasks are only occasionally performed...100 LUX
- Performance of visual tasks of high contrast or large scale.........300 LUX
- Performance of visual tasks of medium contrast or small size........500 LUX
- Performance of visual tasks of low contrast or very small size.....1000 LUX

In LED specifications:

- lm is lumens - total luminous flux flowing from the LED. mlm = millilumens.
- cd is candelas - the luminous intensity at a specific forward current. mcd = millicandela.

Cd or mcd units are usually expressed as a value relative to the viewing angle. The larger the viewing angle, the more light flows given the same intensity. In other words, 1000 mcd over 130° viewing angle is a lot brighter (more lumens) than 1000 mcd over 20° viewing angle. Lumens (lm or mlm) usually refers to the total light output of the device at the rated current.

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