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How to Convert from Watt/sq. cm (at 555 nm) to Phot [ph]
Learn how to convert radiant power measured in watts per square centimeter at 555 nm into illuminance expressed in phot units, an older photometric unit, to aid lighting design, vision science, and photobiological safety assessments.
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Watt/sq. cm (at 555 nm) to Phot [ph] Conversion Table
| Watt/sq. cm (at 555 nm) | Phot [ph] |
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| Watt/sq. cm (at 555 nm) | Phot [ph] |
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What Is This Tool?
This converter transforms values from watt per square centimeter at the wavelength 555 nm, a radiometric measure, into phot units, which represent illuminance. It facilitates interpreting monochromatic radiant power in terms of photometric brightness related to human visual response.
How to Use This Tool?
- Enter the irradiance value in watt per square centimeter at 555 nm.
- Select watt/sq. cm (at 555 nm) as the input unit and phot [ph] as the output unit.
- Run the conversion to get the equivalent illumination in phot units.
- Interpret the results for lighting, scientific, or safety purposes.
Key Features
- Converts monochromatic irradiance at 555 nm to photometric illuminance.
- Uses the luminous efficacy factor of 683 lm/W for conversion.
- Suitable for applications in lighting design, vision science, and photobiological testing.
- Expresses results in the phot unit, historically used for high illumination levels.
Examples
- 0.5 Watt/sq. cm (at 555 nm) equals 341.5 Phot [ph].
- 2 Watt/sq. cm (at 555 nm) converts to 1366 Phot [ph].
Common Use Cases
- Calibrating light sources and photometers for lighting standard compliance.
- Quantifying stimulus levels in vision and psychophysics research targeting the photopic peak.
- Determining exposure limits in photobiological safety tests involving green optical sources.
- Interpreting historical lighting and photographic exposure tables.
- Specifying high brightness studio or indoor lighting levels in older technical documents.
Tips & Best Practices
- Ensure the measurement wavelength is exactly 555 nm for accurate conversion.
- Use the converter for monochromatic irradiance rather than broadband sources.
- Consider the phot unit's historical context when applying results to modern practices.
- Verify instrument calibration when performing experimental conversions.
- Understand that this conversion reflects ideal photopic luminous efficiency conditions.
Limitations
- Conversion is valid only at the monochromatic wavelength of 555 nm.
- The phot unit is not part of the modern SI system and sees limited current use.
- May not account for spectral differences or instrument calibration discrepancies.
- Not suitable for broadband light sources without additional corrections.
Frequently Asked Questions
- Why is the wavelength 555 nm important for this conversion?
- Because 555 nm corresponds to the peak sensitivity of the photopic luminous-efficiency function, enabling conversion from radiometric irradiance to photometric illuminance.
- What does the phot unit represent?
- The phot is an older, non-SI unit of illuminance equal to one lumen per square centimeter, used to express very high brightness levels.
- Can I use this conversion for broadband light sources?
- No, this conversion applies only to monochromatic irradiance at 555 nm and should not be generalized to broadband sources.
Key Terminology
- Watt/sq. cm (at 555 nm)
- A radiometric unit measuring radiant power per unit area specifically at the wavelength 555 nm.
- Phot [ph]
- A non-SI illuminance unit equal to one lumen per square centimeter, representing high levels of illumination.
- Luminous Efficacy
- The factor (683 lm/W) used to convert radiant power at 555 nm to photometric illuminance.