29.06.2006

page 6 of 8

In short, phototransistors are small devices,

with

good

functionality,

whereas

photodiodes offer high performance at a

larger size.

The opto hybrid SFH 5711 is superior to

both devices in terms of spectral sensitivity

and dynamic range, as it combines high

accuracy over the entire brightness range

with

low

temperature

dependence

and

perfect human eye characteristics. Please

see the SFH 5711 application note for more

information

about

this

high

accuracy

ambient light sensor.

Figure 8 shows the spectral sensitivity of all

OSRAM ambient light sensors. Starting from

standard

Si,

it

has

been

continuously

improved and has reached perfection with

the SFH 5711.

The resulting accuracy of the ambient light

measurement for different lamp types is

shown in Figure 9. There the signals of each

photo detector type for the different light

sources are normalized to standard light A

(2865 K), which is a standard point of

reference for brightness. Figure 9 shows

how the signals of each detector type vary

with respect to the different light sources.

This variation is an indication for the

accuracy of the brightness measurement,

which can be achieved with this detector.

For a standard Si detector, for instance, the

maximum deviation is found between light

bulbs and fluorescent lamps and amounts to

over 90%. The same value is below 2% for

the SFH 5711.

Figure 8: spectral sensitivity of all OSRAM ambient light detectors compared to a

standard Si-photo detector and the human eye (V-lambda)