Energy of a spot in an animation


I have a short question.
I want set the energy of a spot light from 0 to 4.5 in one frame.
In the the beginning of the anim (frame 1) the energy worth is 0, in frame 250 the worth should be 4.5. Between these frames the energy should be also 0 like in frame 1.

In that way i have a second question:
Different properties are shown in the IPO Curve editor, but I didn´t find the curves for the properties of light like the spot lights. Is there a window where these curves are shown und where I can edit these curves?

Thanks for your help

When you I-Key in the buttons window with the spotlight selected you can select Energy. Or you can select it from the IPO window and Ctrl-LMB your Keys.

Then select the Curve menu in the IPO window and change Interpolation Mode to Constant.