Sight for sore eyes

A sensor has been developed that for the first time matches the sensitivity of the human eye, according to its developers. The ambient sensor, called SFH 5711, can automatically adjust a monitor's brightness to that of the ambient light, leading to optimum readability, less power consumption and less strain on the eye.

It is produced by Siemens subsidiary Osram Opto Semiconductors. Like the human eye, the sensor is most sensitive to light at a wavelength of 560nm and can distinguish different levels of llight.

This means that a computer screen will automatically adjust its brightness according to changes in levels of light throughout the day. Small mobile terminals such as mobiles and PDAs will be far easier to read in all lighting conditions, including twilight.

Importantly, this could prevent the rapid onset of eyestrain - a common problem attributed to the brightness of PC and laptop screens that are used in dark surroundings. The sensor can also help drivers by registering ambient light when driving through a tunnel to turn headlights on automatically.

The key to this sensor is a new semiconductor material, patented by Osram. Until now, sensors of this type have used silicon, which does not provide the accuracy and sensitivity inherent in the new material, the make-up of which Osram has declined to disclose.

The 'human' properties of the SFH 5711 come from the new material. It replaces the traditional silicon and has a spectral sensitivity similar to that of the human eye. The logarithmic amplifier IC enables a large brightness range (3 lux to more than 30,000 lux) to be detected with great accuracy without the need for resistors. These resistors are needed with linear detectors so that the sensitivity can be adjusted externally for different brightness ranges. The accuracy of the sensor enables virtually infinite dimming of backlighting systems. The new sensor also has low thermal coefficients.

Dr Christine Rueth, Osram product marketing engineer, explained that normal silicon transistors are very sensitive to the infra-red spectrum, whereas the eye is unaffected, so an eye-sensitive sensor leads to far greater applications.

'The sensors that exist at the moment do not have the high accuracy that the new one offers,' she said. 'The reason for that improved accuracy is that the sensor perfectly resembles the spectral sensitivity of the human eye. It is the first one that really does that.'

According to Rueth, the technology will suit mobile and automotive markets in particular, as not only will the sensor ensure mobile phone displays are clearly visible, even in bright sunlight, but it will also prolong battery life as the display will only operate at full power when necessary.

'If you look at displays then you quickly realise there are two benefits to ambient light sensors, one is the saving of battery life, the other is to enhance visibility. If you try to look at anything in bright sunlight you would have to turn the screen right up to physically see.'

She added: 'Normally if you look at any portable computer or mobile, the display is always on a pre-set value. If it can be adjusted automatically then in most cases, in the office for example, it can be turned down.'

This would, she suggested, save at least 20 per cent of the battery in a standard office environment.

Now being launched worldwide, the sensor is a few millimetres in diameter, requires a supply voltage of 2.3-5 and costs €0.5 (34p).