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Illuminator calculation

 IR illuminators

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Illuminator calculation

 IR illuminators

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Illuminator calculation

 IR illuminators

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IR LEDs radiate out of visible light range, therefore their characteristics cannot be measured in photometric units (lumens, candelas and luxes). Characteristics of IR LEDs are measured in power units (watts, watts/steradian, watts/m2).

 

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In the same time black-white cameras are sensitive in the infra-red range, but their sensitivity is measured in photometric units (lux). Therefore, it is necessary to convert power values to the photometric ones.

 

After selecting IR LED in the Lamp type box, measurement units are changed in the boxes:

 

Light efficiency (lm/watt)>LED efficiency factor (watt/watt)

Spectral efficiency of radiation (lumen / lumen) >Spectral efficiency of IR radiation (lumen / watt)

Light flux emitted by lamp (lm)>Radiant power (watt)

Light flux emitted by Illuminator (lm)>Radiant power (watt)

Axial light intensity (cd)>Axial radiant intensity (watt/Sr)

Illumination (lux)>Irradiance (watt/m2)

 


Light efficiency (lumen/watt)>LED efficiency factor (watt/watt)

 

Instead of light flux (lumen), for measuring IR radiation power watts are used.

Therefore, measurement unit in this box is the efficiency factor of LED, i.e. the ratio of radiant power in the specified IR range to consumed electric power.

 

Efficiency factor of modern IR LEDs is 0.06..0.35. To obtain efficiency factor it is necessary to divide the full radiant power by the consumed electric power.

 

These parameters are given in characteristics of LEDs. If the LED type, efficiency factor or radiant power are unknown, it is recommended to enter in this box efficiency=0.1.

 

Spectral efficiency of radiation (lumen / lumen) >Spectral efficiency of IR radiation (lumen / watt)

 

Black-white sensor sensitivity to IR radiation of different wavelength essentially differs. Between image sensors of different types, there is also a difference in spectral sensitivity.

Color cameras are practically insensitive to infra-red illuminators.

 

VideoCAD considers this difference through in advance calculated and experimentally verified spectral efficiency factors of IR illuminators of different wavelengths.

 

The spectral efficiency factor for IR radiation (lumen/watt) of the specified wavelength and specified type of image sensor is equal to the light flux (lumen) of a halogen incandescent lamp with color temperature Tc=3100K having equal efficiency with IR radiation of the specified wavelength having power of 1 watt for the specified type of image sensor

 

Through the spectral efficiency factor the power of IR radiation is converted to photometric equivalent. This is necessary, as camera sensitivity is measured in photometric units (lux).

 

Cameras' sensitivity in VideoCAD is given to the light from halogen incandescent lamp, according to standard CEA 639 ' Consumer Camcorder or Video Camera Low Light Performance '.

 

Spectral efficiency factors are given for five basic types of image sensors:

 

Standard black-white CCD and CMOS sensors;

 

Sony ExView HAD™ CCD sensors, having increased relative spectral sensitivity to infra-red radiation;

 

Standard color sensors of day/night cameras with color filters (without IR filter).

 

Color filters weaken sensitivity in visible light range more strongly, than in infra-red range. As a result, image sensors of day/night cameras have lower sensitivity in visible light range, or, that is the same, the increased relative sensitivity in infra-red range.

 

Sony ExView HAD ™ sensors of day/night cameras with color filters (without IR filter).

 

Effects from decreasing sensitivity in visible light range by color filters and from increasing sensitivity in infra-red range due to Sony ExView HAD ™ technology are added. Such image sensors have the highest relative sensitivity in infra-red range.

 

Standard color sensors with color filters and IR filter. Color cameras are practically insensitive in infra-red range.

 

During modeling images, VideoCAD automatically calculates efficiency of each illuminator depending on image sensor type of the active camera.

 

Reflecting ability of different objects differs in light of incandescent lamps and in IR light. Spectral efficiency factors are obtained from tests with white paper and a human body.

 

Example 1: Scene is illuminated by halogen incandescent lamp with color temperature Tc=3100K, the luxmeter shows illumination of 0.1 lux.

To reach exactly the same image from the camera at illumination from IR illuminator with the spectral efficiency factor of 50 lumen/watt, IR illumination should be 0.1/50=0.02 watt/m2.

 

As color cameras are insensitive to IR radiation, for them the spectral efficiency factor of IR radiation is equal to zero.

 

During design it is not necessary to change these factors.

 

Light flux emitted by lamp (lumen)>Radiant power (watt)

 

Instead of light flux (lumen) for measuring IR power watts are used.

After specifying the consumed power, in the box the total radiant power of IR LED (watt) is displayed. Total radiant power of IR LED is calculated from consumed power and efficiency factor of the IR LED.

 

You can enter in this box the value from LED specification for more accurate modeling.

 

Light flux emitted by Illuminator (lumen)>Radiant power (watt)

 

It is projector radiant power within the limits of the radiation angle. The projector radiant power is equal to the sum of radiant powers of all LEDs  (if they are several), multiplied by efficiency factor of the illuminator.

 

Axial light intensity (candel)>Axial radiant intensity (watt/steradian)

 

Instead of light intensity (candelas) for measuring IR radiant intensity the watt/steradian is used.

It is an axial IR radiant power.

It is the most important parameter of the illuminator. All previous parameters are used for estimation of the radiant intensity.

 

If in specification of IR illuminator the radiant intensity curves are given, it is necessary to reach by selection of Radiant power (watt) equal value of an axial radiant intensity.

 

If in specification there are no radiant intensity curves, but there is a value of the axial radiant intensity, it is necessary to select value of the Radiant power to obtain equal axial radiant intensity.

 

If in the specification there are no such parameters, or the specification is absent, only estimation is possible.

 

Specify:

Efficiency factor=0.3 for the narrow angle luminaire (radiation angle of 20-50 degrees);

Efficiency factor=0.5 for the wide-angle luminaire (radiation angle of 60-120 degrees).

Concentration =0.5.

 

In practice the estimation is enough.

 

Illumination (lux)>Irradiance (watt/m2)

 

Instead of Illumination (lux), the Irradiance (watt/m2) is used.

 

 

See also: Illuminator calculation, Lamp parameters, Luminaire parameters, Illuminator, Current construction parameter panel>Illuminator, 3D Video>Image parameters panel>Scene.