Hi,

Here you can see the rise time and fall time of a LDR.
(@10 lux and @1000 lux).
http://docs-europe.electrocomponents...6b8001a9d6.pdf

NORPS-12 CdS Photocell:
http://docs-europe.electrocomponents...6b8003484c.pdf

(The above two links are from the RS Components Ltd web server).

* * *

Use a phototransistor.

Best regards,

Luciano