External Light Meter is a standalone device for measurement of brightness on the subject which is measured in SI unit of illuminance lux (lx) for the exposure. Many thinks that an external light meter is not needed in Digital Photography. It is actually a wrong concept. Right quoting from one experienced and aged photographer’s comment from a forum – “It’s pretty much required for serious studio work and pretty much not necessary for landscape work.” We wrote about Studio Setup before. Now it is required to combine the old read (if already read) knowledge with this article’s knowledge.
Basics of an External Light Meter
First method to determine the proper exposure of the photographic material was thought since 19th Century and photochemical processes were used, in which the blackening of a treated with a photosensitive material was observed with the eye and was compared with a comparison example scale.Now, typically an external light meter allows the photographer to determine which shutter speed and f-number for an optimum exposure, in a certain given lighting situation and film speed.
Modern external light meter for measuring light uses one light sensor. There are of photoresistors and photodiodes varient. The light sensor must have a spectral sensitivity of the luminosity curve of the eye and needs to be adjusted.
Newer equipments and external light meters often work with a cadmium sulfide (CdS) photoresistor. The resistance profile of photoresistors is strongly nonlinear, so often no range switching is necessary.
More on External Light Meter
Now, some readers will rightly ask at this point the question, that why we (still) requires an external light meter ? Well, it can not be dismissed out of the hand, that the importance of an external exposure meter has decreased significantly by digital photography, because modern cameras have built with an internal light meter.
Nevertheless, the external light meter has retained its place in some areas. Especially in the area of studio photography – it makes the external light meter useful. Also in the photograph of the exposure of buildings is usually more accurate than the measurement than that of the internal light meter of the camera works better. Shooting at night, this external light meter allows the to measure the exposure time correctly. The only drawback is the cost of the acquisition and the extra weight in your bag, but that is negligible. Exposure meters can measure all types of lighting (daylight and flash) and are priced accordingly.