Yes, it is possible to convert illuminance to irradiance for a single wavelength if you have the necessary information. Illuminance refers to the amount of light falling on a surface per unit area and is typically measured in lux (lx), while irradiance refers to the power of light incident on a surface per unit area and is typically measured in watts per square meter (W/m²).
To convert illuminance to irradiance for a single wavelength, you would need to take into account the photopic luminance weighting factor, which represents the sensitivity of the human eye to different wavelengths of light. The photopic luminance weighting factor is often represented by the luminous efficiency function, also known as the photopic spectral sensitivity curve.
The photopic spectral sensitivity curve describes the eye's response to light at different wavelengths, and it is typically based on the CIE (Commission Internationale de l'Eclairage) standard curves. The CIE has defined a standard spectral luminous efficiency function called V(λ) (also known as the photopic luminous efficiency function), which represents the average human eye's response to light.
To convert illuminance (in lux) to irradiance (in W/m²) for a single wavelength, you would follow these steps:
Obtain the photopic luminance weighting factor for the specific wavelength of interest. This can be obtained from the photopic luminous efficiency function V(λ) or the appropriate CIE standard curves.
Multiply the illuminance (in lux) by the photopic luminance weighting factor. This will give you the luminous flux for that specific wavelength.
Convert the luminous flux from lumens (lm) to radiant flux in watts (W) by multiplying it by the luminous efficacy of radiation (LER) for that specific wavelength. Luminous efficacy of radiation is the ratio of the luminous flux (lm) to the radiant flux (W) and is specific to the wavelength.
Divide the radiant flux (W) by the surface area (in square meters) over which the illuminance is measured. This will give you the irradiance (W/m²) for the single wavelength.
Please note that this conversion assumes a monochromatic light source at a specific wavelength and considers the response of the human eye according to the photopic luminance weighting factor.