filtratielichtheid

Filtratielichtheid is a term used in optics and photometry to describe the level of light that passes through a filter relative to the incident light. It is essentially the transmittance of a filter expressed in a lightness scale, often as a percentage or in terms of optical density. The concept is important for controlling illumination in laboratory experiments, photography, and optical engineering where precise light budgets are necessary.

The calculation of filtratielichtheid usually starts with a measurement of the incident intensity (I₀) and the transmitted intensity (I). The transmittance T is given by the ratio I/I₀, which is then converted to a lightness value. In many applications, especially in printmaking and photographic film, the optical density (OD) is used, defined as OD = –log₁₀(T). A higher OD indicates a darker filter that blocks more light.

In practice, filtratielichtheid guides the choice of filters for tasks such as reducing glare, adjusting color temperature, or protecting sensors from overexposure. Neutral density filters, which uniformly reduce light across the spectrum, are often specified by their transmittance value (e.g. 10 % transmittance corresponds to 1.0 OD). Colored filters, on the other hand, influence filtratielichtheid differently across wavelengths, which is exploited in color imaging and spectroscopy.

Measurement of filtratielichtheid is typically performed with a spectrophotometer or photodiode array, ensuring that the spectral distribution of the incident light is known. Accurate knowledge of filtratielichtheid allows designers to predict system performance, calibrate instruments, and maintain consistency across repeated exposures.