Understanding basic photoresistor circuit
The HW5P-1 is in fact a phototransistor.  

This is the diagram of the example circuit from the datasheet:



The circuit symbol is clearly a phototransistor, regardless of what the poorly translated text says.

A phototransistor and a photoresistor (like a cadmium sulfide cell) both react to light, but they are fundamentally different in how they operate.

A photoresistor is a resistor whose resistance changes in response to light.

A phototransistor actually generates current from light in its base to emitter junction, which allows current to flow through the collector to the emitter.  It is in effect a tiny solar cell connected to a single transistor amplifier.

You can use both to detect light, but you should familiarize yourself with how they work.

A short list of differences:


Photoresistors are slow.  You can't really receive a modulated light signal with them.  Phototransistors are much faster, and can pickup light signals modulated with signals that can reach megahertz frequencies.
Photoresistors keep changing resistance even after the light is gone.  Datasheets specify the "dark resistance" for a time period in absolute darkness for this reason.
Photoresistors are usually most sensitive to visible light.  Phototransistors are usually most sensitive to infrared.  Results can be very different from what you expect if you just replace a photoresistor with a phototransistor without considering that difference.
They have different response curves.  If you use the same circuit with both, they will react differently to the same light intensity.  This might change your threshholds if you are using a simple level detector.


So, really, they aren't the same so don't use the terms interchangeably.  

They can carry out similar tasks, but you have to use each as intended. Using one just like the other will lead to bad results.