Making a phototransistor behave equally in sunlight

[ACharnley]

Just after some quick thoughts.

I've a photo transistor which was specifically chosen to block infrared. This it appears to do, however during day[sun]light the read is double that of a head-torch shining on the sensor. As a quick test I held a lighter flame close and it blows out the sensor read.

I'm thinking I need to filter the red and possibly yellow component, so a blue filter. Does this sound correct?

 

[Nigel Goodwin]

Just after some quick thoughts.

I've a photo transistor which was specifically chosen to block infrared. This it appears to do, however during day[sun]light the read is double that of a head-torch shining on the sensor. As a quick test I held a lighter flame close and it blows out the sensor read.

I'm thinking I need to filter the red and possibly yellow component, so a blue filter. Does this sound correct?

Sun light is massively brighter than a torch, so it sounds like it's behaving exactly as it's supposed to.

 

[schmitt trigger]

Why would you want to filter out some colors? The sunlight is full spectrum, whereas any artificial light, specifically the fluorescent and LED ones, will have significant spectral gaps.
Incandescent lamps are also continuous spectrum, but leaning very heavily towards the red.

 

[schmitt trigger]

Figure 4 you posted indicates that the detector’s maximum sensitivity occurs around 625 nm, which is a reddish-orange. Small wonder that a flame causes it to react.