The one parameter that determines that brightness of a light source sensed by an eye is

Options

A. energy of light entering the eye per second
B. wavelength of the light
C. total radiant flux entering the eye
D. total luminous flux entering the eye

Answer

To determine the brightness of a light source as sensed by the human eye, we need to analyze the given options carefully. The question asks for the one parameter that influences perceived brightness. Let's go through the options step by step.

### Step-by-Step Solution:

1. **Understanding Brightness**: Brightness is a subjective perception of light intensity by the human eye. It is influenced by various factors, but we need to identify the most relevant parameter from the options provided.

2. **Evaluating the Options**:
- **Option 1: Energy of light entering the eye per second**: While energy is important, it does not directly correlate with brightness perception. Different light sources with varying energy levels can still appear similarly bright.
- **Option 2: Wavelength of the light**: The wavelength affects color perception but does not determine brightness. Two lights of different wavelengths can have the same brightness.
- **Option 3: Radiant flux entering the eye**: Radiant flux refers to the total power of light (in watts) entering the eye. However, it does not directly measure how bright the light appears to the observer.
- **Option 4: Total luminous flux in the eye**: Luminous flux is a measure of the perceived power of light, weighted by the sensitivity of the human eye to different wavelengths. This is the most relevant parameter for brightness perception.

3. **Conclusion**: After analyzing all options, the one parameter that determines the brightness of a light source sensed by the eye is the **total luminous flux in the eye**. Therefore, the correct answer is **Option 4**.

### Final Answer:
The one parameter that determines the brightness of a light source sensed by an eye is **total luminous flux in the eye**.

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