The scene is compared to the light from a small bulb. A rheostat controls the brightness of the bulb. A variable density wedge can be placed in front of the bulb. Made in France.

In use a dial is turned which diminishes the brightness of the image of a filament. When the brightness of the filament blends into the subject the correct exposure is shown. The meter has to be calibrated before use to compensate for eyesight, battery and bulb strength. Only one film speed is indicated.

Light from the bulb is standardised by measuring its output with a photoelectric cell and adjusting with a rheostat to align the needle of a galvanometer. Three measuring ranges are obtained by introducing neutral density (ND) filters into the telescope. The colour of the light source can be set. The price was £36.0.0. Accessories included a densitometer fitting.

SEI was part of the British General Electric Co.

This is a simple spot comparison meter where the subject is viewed through a finder and a separately illuminated spot is seen in the field of view. The spot is an image of a small screen that is illuminated by an electric lamp which lies at a variable distance from the screen. The meter is adjusted by varying this distance until the spot matches with the subject. The lamp is fixed in an inner tube connected by a slot and pin to an outer tube, turning the inner tube varies the distance of the lamp to the screen. As the lamp to screen distance is altered the illumination of the screen changes according to the inverse square law, the slot is cut in such a way that the exposure scales on the instrument have uniform divisions, i.e. the angular movement to linear movement varies.

The meter was at first marketed as the Ainger Hall.