Please correct me if i am wrong.My understanding is that you want to measure light intensity through comparison method.To measure the intensity of light using another standard setup you have to calibrate your instrument first and then you have to use it for measurement.Use a 10 turn POT to control the intensity of LED light connected in series with Battery and Light.Using a marked scale and a pointer attached on a string connected to the Knob mounted on the pot and pulley on the other side can be helpful.

I understand what is UV/VIS photometer, but what is the LED doing there? Or, do you need a simple photometer to measure the properties of the UV - LEDs and VIS-LEDs ?

Agunloye,

If you are wishing to *measure* UV/VIS light then you'll need a photodiode - not an LED. An LED emits light - and you want the opposite.

So. For less than a dollar of parts, a simple amplifier will suffice:

https://makezine.com/projects/make-38-cameras-and-av/light-and-dark-sensors/

Photodiodes with UV sensitivity can be found. Or one can use broadband sensors and filters.

This is more complex:

http://redlum.xohp.pagesperso-orange.fr/electronics/photometer.html