Briefly explain the operation of a photographic lightmeter.

A light meter works by measuring the amount of light in a scene, usually in units called lux or foot-candles. It uses a light-sensitive sensor (usually a photovoltaic cell) to detect the light and convert it into an electrical signal. This signal is then processed by the device, which displays the exposure settings (aperture, shutter speed, and ISO) that will give the best results for the photograph.

The main function of a light meter is to calculate the Exposure Value (EV), which is a number representing the optimal settings for taking a photograph. The measurement of light is combined with other factors like ISO and aperture settings, to suggest the appropriate shutter speed for a photograph. This information is provided as a guide for photographers to achieve the correct exposure, helping to avoid underexposed or overexposed photos.

Incident light meters measure the light that directly falls onto a subject. For taking measurements, the light meter is placed between the light source and the subject, facing the light source. The meter measures the amount of light falling on the subject and calculates the exposure settings accordingly. This type of meter is ideal for accurately measuring the amount of light illuminating the subject and providing exposure settings for evenly lit images. Incident lightmeters are usually handheld devices.

Reflected light meters, often found within cameras, measure the amount of light that bounces off a subject and back to the meter. They measure the light that the camera will see and are particularly useful in situations where the lighting is uneven. However, they can be easily affected by variations in the reflectivity of the subject and the scene's background, potentially leading to less accurate readings. To counter these issues, photographers can use a gray card, placed near the subject, to obtain a more accurate measurement. In conclusion, a photographic light meter operates by measuring light in a scene, calculating exposure values, and providing recommendations for optimal exposure settings. The two main types of light meters, incident and reflected, offer different ways to measure light and can be employed to achieve the desired photograph.