# Phototransistor vs LDR

1. Oct 20, 2006

### flash

Hi,
I'm wondering what the difference between a light dependent resistor and a phototransistor is. Am i correct in assuming they are the same if the third lead of the phototransistor is not connected to anything?
Thanks!

2. Oct 21, 2006

### Hootenanny

Staff Emeritus
From my somewhat limited experience with electronics I seem to recall that phototransistors can amplify the current produced and therefore have a greater sensitivity that of a photodioide, the response times are slower however. This question may be better placed in the Engineering forums (perhaps Berkeman could take a look).

3. Oct 21, 2006

### Reshma

Yes, this question should be in one of the Engineering forums.
A photodiode has an ability to produce large light to dark current ratio. The current produced by a photodiode is of few micro-amperes. A normal transistor has a property to amplify the input current by $\beta$ times where $\beta$ ranges from 50 t0 300 and is known as current amplification factor. A Phototransistor combines the advantages of a photodiode as well as a normal transistor.

LDR as the name suggests is a Light Dependent Resistor whose resistance changes according to the intensity of the light incident on it.