Radiometry and radiometric units such as radiant flux relate to properties associated with the energy of electromagnetic radiation (which for LEDs we'll refer to as "light" - this term covers visible light, as well as UV and IR radiation).

Photometry
Photometry and photometric units such as luminous flux relate to the properties of light with reference to the sensitivity of the human eye (i.e. when the eye is the sensor).

The radiant flux or radiant power of a light-emitting body is the total rate of flow of emitted light i.e. the total radiant energy per unit time.
* Units: watts (W)

The radiant flux per unit solid angle - in other words, the optical power in a given direction.

The ratio of the radiant flux (photons produced = Watts out) to the amount of power consumed (electrons used = Watts in) i.e. how efficiently the source converts electrical power into light. Also known as wall-plug efficiency.
Radiant efficiency (wall-plug efficiency) = optical power / electrical power
* Units: none (ratio)

PHOTOMETRIC PROPERTIES

As stated above, photometric properties takes account of the sensitivity of the human eye to different wavelengths of light.

 Eye sensitivity curve
This sensitivity is defined by the CIE V(λ) curve which plots the eye sensitivity function V(λ) against wavelength (see graph). The CIE curve shows that the eye’s peak sensitivity occurs at 555 nm, and is 3 orders of magnitude lower at 390 nm and 720 nm.

Luminous flux
Luminous flux measures the total radiant flux across the spectrum, weighted by the sensitivity of the human eye to different wavelengths i.e. weighted by the V(λ) curve.
* Units: lumen (lm)
The lumen is an SI unit derived from the candela (see below): lumen = candela.steradian.

Luminous intensity
For a point source, luminous intensity is the luminous flux per unit solid angle (i.e. flux in a particular direction)
* Units: lumens/steradian (lm/sr), equivalent to candela (cd)
The candela is an SI unit defined as the luminous intensity in a given direction of a source that emits monochromatic radiation of frequency 540 x 1012 Hz (equivalent to a wavelength of 555 nm) and that has a radiant intensity in that direction of (1/683) watt per steradian.

Luminance
Luminance is the luminous intensity per unit emitting area for a non-point source. To the observer, the property of luminance corresponds to the brightness of the source.
* Units: candela/square meter (cd/m2), equivalent to nit

Note that for any source it is not possible to increase either the flux or the luminance.

Luminous efficacy
Luminous efficacy measures how effectively the eye converts radiant flux into a visual sensation.
Luminous efficacy of a source (often called simply “luminous efficacy” or “source efficacy”) is the ratio of output luminous flux (lm) to input electrical power (W).
Luminous efficacy of radiation is the ratio of luminous flux (lm) to radiant power (W), and is therefore the theoretical maximum that a light source with a given spectral distribution can achieve with 100% radiant efficiency.
Based on the definition of a lumen, the theoretical maximum value of luminous efficacy is 683 lumens/watt for a monochromatic 555 nm source that converts all electrons to photons.
* Units: lumens/watt (lm/W)

Illuminance
Illuminance is the density of the luminous flux incident on a surface. Its value is determined by luminous intensity, angle of incidence and distance from the source to the surface.
* Units: lumen/square meter (lm/m2), equivalent to lux.
* Alternative unit: foot-candle, equivalent to lumen/foot2. To convert from foot-candle to lux, multiply by 10.764.

# RELATED COMPANIES

## Cree Inc

Leads the LED industry in performance, brightness and reliability with its XLamp LED family, enabling the lighting industry with efficient, environmentally-friendly LEDs that produce beau...

## Zierick Manufacturing Corp

Offers innovative solutions for interconnect applications. Specializes in wire-to-board and board-to-board applications. Provides surface mount and thru-hole products while further reduci...

## InnoLight sp zoo

EU located lighting manufacturer for LED GU10 5W 600lm CRI>80 reflector, great performance, and LED E27 5W 380lm classic traditional appearance.

## Colorimetry Research

Specializes in the field of optics, manufacturing, electronics and software enables us engineer products with the right balance of hardware and software.

## eldoLED America Inc

Designs and manufactures drive solutions for LED based lighting systems. Our technologies empower our customers to deliver the promise of LED lighting.

## Cirrus Logic Inc

Cirrus Logic develops high-precision, analog and mixed-signal integrated circuits for a broad range of innovative customers across a variety of energy-related applications, including the ...

## LEDSupply

Established in 2002 as an ecommerce store for all your LED product needs.

## CINCON

Designer and manufacturer of custom and industry standard LED, DC-DC and AC-DC power supplies from 1W to 1600W. Cincon also designs and manufacturers lighting controllers, interfaces...

## Illumination Machines

Illumination Machines designs custom optics, heat sinks, and remote phosphor systems for LED luminaires and lamps.

## eldoLED BV

eldoLED is a world leader in the design and manufacture of intelligent drive solutions for LED based lighting systems. Our technologies empower our customers to deliver the promise of LED...

## CSA Group

A global solutions provider of product testing and certification services for electrical, mechanical, plumbing, gas, medical and a variety of other products.

## Energy Efficient Lighting

Energy Efficient Lighting offers total solutions to both conventional and more advanced LED lighting fixtures and LED retrofit kits for commercial and industrial applications.

## Schréder

48 companies worldwide, passionate about light and innovation, experts in developing LED lighting solutions for safe and comfortable environments with significant energy and cost savings,...

## Guardian Industries

Guardian Industries Corp. is a leader in float glass, fabricated glass and high performance coated glass products. Guardian lighting solutions deliver optimal performance, flexibility and...

## ELMA Electronic Inc

Provides standard and customized LED solutions. Elma's LED family offers consistent, reliable, and durable illuminating and indicating solutions.

## LEDSAmerica Inc

LedsAmerica is a full line LED line company and has manufacturing in Iowa where T8 LED-O tubes and street lights are made together with PL, PARs, High Bay lights. MAx

## Lumentra Inc

Provides NVLAP accredited optical (photometry, colorimetry, Lumen maintenance), thermal (mapping and transient analysis), electrical characterization services, product development, supply...

## CINCON USA

The LED, DC-DC and AC-DC power supplies from 1W - 1600W. Cincon’s lighting controllers, interfaces and devices incorporating DALI protocol. LED drivers from 25W - 150W with international ...

## LTF LLC

LTF, LLC is a U.S based solid-state lighting product development and manufacturing company with facilities located in both USA and China.

## Marian Inc

Marian is a global company who supplies die cut and converted parts to the LED market. Materials include thermal pads, reflective, venting, gaskets, insulators, diffusers and more.

# RELATED PRODUCTS

## Surface Mount Wire Gripper - Part Number 1301

The Zierick 1301 is designed to allow customers to easier terminate a stripped wire to a PCB. Wire sizes to 24 AWG. Terminal is UL Recognized.

## Surface Mount Wire Gripper - Part Number 1262

The Zierick 1262 is designed to allow customers to easier terminate a stripped wire to a PCB. Wire sizes from 0.025" to 0.095". Terminal is UL Recognized.

## Unlock new LED lighting solutions with Cree High Density LEDs

Cree® High Density LEDs deliver the industry’s highest optical control factor enabling lighting manufacturers to improve performance, cost and size of LED lighting—enabling never before p...

## Cree CXA LED Array Family

Cree’s CXA LED Arrays are optimized to simplify design and lower system cost, delivering high lumen output and efficacy with a family of single, easy-to-use arrays.

## Cree LED Modules

Cree LED modules deliver beautiful, consistent light, backed by a 5-year warranty. They offer a choice of dimming options, while reducing the lighting power load by 80%.

## Cree XLamp® XP-L LEDs-the industry’s highest efficacy single-die LED.

Cree® XP-L LED is the first commercially available single-die LED to achieve up to 200LPW at 350mA. The XP-L enables 50% or more performance increase as a drop-in upgrade.

## Cree XLamp® XM-L2 EasyWhite® LED

The first 5mmx5mm LED to enable color-consistent 50W halogen performance; the XM-L2 EasyWhite delivers 1,100 lumens and is optimized to replace halogen technology.

## Surface Mount Insulation Piercing Terminals

Surface Mount Wire-to-Board terminals available for wire gauges ranging from 24 to 14 AWG. Parts can be terminated to allow daisy-chain applications. Eliminates difficulty with direct...

## LED light Bulb – LED spotlight

The AR111,GU10,MR16,PAR30,PAR38 LED bulbs are ideal replacement of 10-75W halogen or CFL bulbs.Cree/Everlight LEDs.PMMA lens.Aluminum housing.Good heat dissipation.Surface temperature les...

## Super bright Injection LED modules

Housed by ABS material,covered by epoxy resin on surface with good insulation.Beautiful appearance.Waterproof.Anti-fire.Super bright 5050/3528 LED.12V voltage.Ideal light source for backl...

## Flexible LED screen - Rental and Stage LED billboard

Special design,flexible use,light weight,super slim,transparent,SMD technology,easy to install.Can realize any curved and creative installation horizontally and vertically.IP65 protection...

## LED flexible strip and aluminum LED bar

Full range of LED strip and bar including the unique high lumen strip. Protection degree up to IP68.Epistar 3528/5050 SMD LED.Compliant with CE & RoHS.2-year warranty.3528: 60LED/m,120LED...

## P3 Indoor Full Color LED Display Video screen

High-density pixel pitch,high resolution,high refresh rate,magnificent and high-definition image and video effect.P3,P5,P6,P7.62 to P10 available.Epistar SMD LED,wide viewing angle.High r...

## LED Panel Light

Designed to replace T8 fluorescent tube or Phillip Grille light.Epistar 3528/3014 SMD LED.Aluminum alloy body.Even and Soft light beam.Various mounting means.50,000 hours lifetime.Environ...

## Rotatable LED Down Light, beam angle adjustable 10-60°

Beam angle adjustable 10-60 degree.Shell can rotate 360°,vertical 0-40°.High power CREE LED,even and uniform light output,Die casting aluminum alloy housing,good heat sinking.Widely used ...

## Solar LED Paver Light

100% solor powered.No wires, no electricians.Super capacitors instead of battery,maintenance-free.Absorb sunlight in daytime and illuminate 8-12 hours during night. Epistar LED.Activation...

## T8 LED tube light

Epistar Super bright 3528/2835 SMD LED.Aluminum alloy body with plastic cover.Consist with traditional fluorescent tubes.Easy mounting.PF>0.90,CRI>72,Over 60% energy-saving,Low degradatio...

## 360 degree 10W led bulb

360 degree 10W led bulb has high efficiency, high power factor，environmental friendly, unique heat-dissipating design and perfect thermal management.

## iVAR COB LED Downlight

iVAR COB LED Downlight use die-casting magnesium alloy to make the main body,has Excellent heat dissipation performance,and Unique and delicate looking design.

## LIMS - Liquid Injection Molding System

Silicone LIMS can be used to injection mold silicone components such as lenses or gaskets in an automated process. The two-component, thermoset material ranges in Shore A hardness from 5-80.

# SOCIAL ACTIVITY

Miss a webcast? Watch it in the archives

Our weekly flagship news source
SUBSCRIBE