What Is a Luminometer?
A luminometer is a type of human-detecting sensor that detects ambient light.
It has a function to automatically turn on the light when the surroundings become dark and automatically turn off the light when the surroundings become bright. It also adjusts the brightness of the display to a level that is just right for human senses. There are three main types of luminometers: phototransistors, photodiodes, and photodiodes with an amplifier circuit.
Luminometer is a technology that contributes to reducing the power consumption of electronic devices and improving the quality of display screens.
Uses of Luminometers
Luminometers are widely used to detect the brightness of displays and LCD screens and to measure ambient illuminance to automate lighting on/off.
For example, in cell phones and smartphone devices, illuminance sensors contribute to improved visibility and lower power consumption of LCD screen displays by enabling control of LCD backlight brightness in response to ambient brightness. Once mounted on a display, it can automatically adjust visibility.
It is also one of the technologies in growing demand and being adopted in a wide range of fields including cameras and optical communications.
Principle of Luminometers
Illuminometers use photodiodes and phototransistors that convert the illuminance of light incident on the light-receiving part into an electric current, which is sensed by converting the actual brightness of the light into an electrical value through a circuit that amplifies the output current to a current value usable for the sensor function.
In other words, the current flowing through the phototransistor changes according to the brightness, and this causes a voltage corresponding to the brightness to appear at both ends of the resistor installed in the circuit, thus detecting light.
In addition, the photosensitive element must have a minute sensitivity characteristic in the same range of wavelengths that can be sensed by the human eye. However, photodiodes generally used in photodetectors are sensitive outside the infrared region, which is invisible to the human eye, and thus requires compensation.
By installing a sub-photodiode with a peak spectral sensitivity in the infrared region, the sub-photodiode is subtracted from the main photodiode. This mechanism enables the sensor to have spectral response characteristics close to the visual sensitivity that the human eye can perceive.
Other Information on Luminometers
1. Output Configuration of Luminometers
There are various types of luminometers, ranging from very simple ones that convert the output current from the photodiode or phototransistor in the light-receiving part into a voltage value using an analog circuit and output it, to more sophisticated ones that have an analog-to-digital converter, a digital control unit, and a serial interface such as SPI.
With an SPI interface, control from a microcontroller or other device is relatively easy via software and can follow the control of detailed applications. Usually, in such cases, a small dedicated IC that is converted into a sensor ASIC is used to realize a compact and highly functional luminometer product.
2. Illuminometer Sensor Switch
An applied product using luminometers is an illuminance sensor switch. Using this switch, room lighting can be automatically turned on and off according to the external brightness. For example, in a large office, there is usually a lighting switch for each area, and the lighting is turned on and off from that switch.
The advantage of installing lighting sensor switches is that lighting can be automatically turned on and off according to external brightness. Highly functional luminometer switches can also be used to dim the lights depending on the illuminance. These functions can be set from a controller installed separately from the luminometers.
From the controller, it is possible to set the level of illuminance at which the lights are turned on or off, the day of the week, and the time of day when the function is enabled. Some luminometers allow the illuminance setting to be changed depending on the season.
By installing such luminometers in offices, etc., it is possible to appropriately control the illumination level of various indoor lighting depending on the time of day, the season, and the weather conditions outside. Such efforts will result in energy savings.