What is an apostilb and where is it used?

The apostilb is a historical unit of luminance representing 1/π candela per square meter, frequently used in older photometric data, cinematography, and lighting engineering literature to describe surface brightness.

Why is the conversion specific to 555 nm wavelength?

The 555 nm wavelength corresponds to the photopic peak of human visual sensitivity, allowing radiometric measurements to align with how the human eye perceives brightness.

Can I use this conversion for wavelengths other than 555 nm?

No, this conversion only applies at 555 nm. Radiometric spectral radiance at other wavelengths needs different conversion factors.

How to Convert from Apostilb to Watt/sq. cm/steradian (at 555 nm)?

Learn how to convert luminance from the apostilb unit to watt per square centimeter per steradian at 555 nm, bridging historical photometric data with precise radiometric measurements aligned to human visual sensitivity.

Apostilb

Watt/sq. cm/steradian (at 555 nm)

Please check your input. It must be a valid numeric value.

Apostilb to Watt/sq. cm/steradian (at 555 nm) Conversion Table

Apostilb	Watt/sq. cm/steradian (at 555 nm)

Custom Unit Conversion Table Generator – Instant Printable Conversion Tables

Start Value

Enter the starting number (positive decimal or integer ≥ 0). Example: 0.1, 1, 5.

End Value

Enter the ending number (positive decimal or integer > Start Value). Example: 10, 50, 100.

Interval

Enter the step size (positive decimal > 0 and < End Value – Start Value). Example: 1.0, 2.5.

Apostilb to Watt/sq. cm/steradian (at 555 nm) Conversion Table
Apostilb	Watt/sq. cm/steradian (at 555 nm)

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What Is This Tool?

This converter transforms luminance values measured in apostilbs, a traditional photometric unit, into watt/sq. cm/steradian at 555 nm, a radiometric unit referencing the photopic peak of human vision. It aids in interpreting and comparing luminance data in different measurement systems.

How to Use This Tool?

Enter the luminance value in apostilbs you wish to convert
Select apostilb as the input unit and watt/sq. cm/steradian (at 555 nm) as the output unit
Click the convert button to obtain the corresponding radiant spectral radiance value
Use the result to analyze or calibrate luminance data with respect to human visual sensitivity

Key Features

Converts luminance from apostilb to watt/sq. cm/steradian at 555 nm
Supports analysis linked to human visual sensitivity at the photopic peak
Facilitates comparison between historical photometric and modern radiometric data
Useful for display manufacturing, vision research, and optical calibration

Examples

5 apostilb equals 5 × 4.6604668548139e-8 = 2.33023342740695e-7 watt/sq. cm/steradian (at 555 nm)
10 apostilb equals 10 × 4.6604668548139e-8 = 4.6604668548139e-7 watt/sq. cm/steradian (at 555 nm)

Common Use Cases

Translating historical luminance measurements into radiometric spectral radiance at the photopic peak
Linking older photometric data with current radiometric standards for analysis and calibration
Specifying or comparing optical output from LEDs, lamps, or displays during photometric testing
Supporting vision science research and optical instrument calibration focused on 555 nm wavelength

Tips & Best Practices

Ensure that luminance measurements correspond to the 555 nm wavelength for accurate conversion
Handle values carefully due to small numerical magnitudes and scientific notation
Use this conversion when integrating historical photometric data with modern radiometric standards
Remember that apostilb is a non-SI, historical unit and may not fit all modern photometric contexts

Limitations

Apostilb is a historical, non-SI unit which may restrict its use in current photometric standards
Conversion is valid only at the 555 nm wavelength tied to peak human visual sensitivity
Different wavelengths require other conversion approaches
Small numerical values can lead to rounding errors requiring careful calculation

Frequently Asked Questions

What is an apostilb and where is it used?: The apostilb is a historical unit of luminance representing 1/π candela per square meter, frequently used in older photometric data, cinematography, and lighting engineering literature to describe surface brightness.
Why is the conversion specific to 555 nm wavelength?: The 555 nm wavelength corresponds to the photopic peak of human visual sensitivity, allowing radiometric measurements to align with how the human eye perceives brightness.
Can I use this conversion for wavelengths other than 555 nm?: No, this conversion only applies at 555 nm. Radiometric spectral radiance at other wavelengths needs different conversion factors.

Key Terminology

Apostilb: A non-SI, historical unit of luminance equal to 1/π candela per square meter, representing luminous intensity emitted or reflected per unit area in a given direction.
Watt/sq. cm/steradian (at 555 nm): A radiometric spectral radiance unit expressing radiant power per unit area and solid angle at the wavelength of 555 nm, linking radiometric and photometric quantities.
Photopic peak: The wavelength near 555 nm where human visual sensitivity to brightness is at its maximum during well-lit conditions.

Quick Knowledge Check

What does the apostilb measure?

Radiant power per unit area

Luminous intensity per unit area in a given direction

Frequency of light waves

Why is watt/sq. cm/steradian measured at 555 nm important?

It corresponds to ultraviolet light

It matches peak human visual sensitivity

It relates to infrared radiation

What limitation should users be aware of when converting apostilb?

It applies to all wavelengths of light

It is a non-SI, historical unit

It is measured in seconds

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