Hi,
That sounds pretty good really and worth building, but often i prefer a human eye to a photo detector of any sort for problems that may involve the oddities of the human eye response. But even without that requirement it's not too hard to build a comparative light detector which allows quick comparison of light sources using the human eye.
The construction is quite simple, and i'll explain the basic construction. You can do it better if you like, but this is the least that works good.
First, find a white candle at the store, probably the kind used for table lighting like around 1 inch diameter. They are usually something like 10 inches long with a skinny end and one fat end. Somewhere along the length the diameter is fairly constant.
Find the place where the diameter is fairly constant over about 1 inch of length, then make a clean cut with a sharp razor blade or maybe hobby saw. That gives you two pieces. The flats of the two pieces should be parallel.
Next, cut about 1/2 inch off of each piece off the ends that were just cut away from each other. That gives you two round pieces of white candle 1/2 inch long each. Discard the rest.
Next, cut a piece of aluminum foil about 3 inches long and about 1.5 inches wide. It's a rectangle shape. Then, fold it over so that the two most shiny surfaces are facing out and the two dull sides in. This forms a piece about 1.5 inches square.
Next, apply some glue to the two dull sides and press the foil together so that it forms one piece two layers thick, then glue one candle piece to each shiny side, wait for the glue to dry.
Congrats! You now have a comparative light detector
After the glue has dried thoroughly, hold the device up in front of you so that you are looking at it from the side. You'll see one candle piece on the left and one on the right.
Shine one light source directly onto the round surface of the left side, and shine the second light source to compare on the round surface of the right side, while still looking at it from the side. Be sure that there is enough light spread to cover the entire round surface of each piece.
What you will see if both sources are the same is the light on the left piece will look equal to the light on the right piece, from the side. If one source is dimmer then you'll see a slight difference.
To use this with the pulsed vs constant current test just shine one on the left and one on the right, and adjust the constant current until the two intensities look equal. When they look equal, you have the correct current needed to match the pulsed light source.
The key to this simple device is the human eye and brain find it hard to remember actual light intensities, but are incredibly good at detecting light differences when there is something in the field of view to compare it to. So even a small difference will be detectable, and what else is key is it is after all the human eye that is doing the comparison not an abstract instrument.