Well, once in a while I get a good idea . . . and that happen just a week or so ago when I was looking for something to hold my phone while in bed (I read books on it and get tired of holding it. Yep, lazy). I came across some cell phone holders and the light bulb went off!
Above you can see my sketch pad on my messy table, and on it is a cell phone holder. The arm is stiff but flexible and holds whatever light I want to put in it or clamped to it there. Here I have an adjustable Photon Red Light at full brightness to show the level of light at maximum you can have here. I have the cell phone clamped on to the sketching pad as it comes with a clamp to do that, and I am using two children blocks (green) to clamp down on the sketching pad. The blocks allow me to have a firmer clamp on the sketching board. I like the Photon the best since I can use a eye patch on my left eye to keep it dark adapted, and then use the right eye to sketch. In addition I usually have it at its lower to lowest setting. You can see the diamond shape photon lamp clamped on the bottom of the cell phone holder above. I like that it clamps also unto the cell phone holder.
Here are some more pictures.
A Rigel StarLite Light at full brightness, not adjusted down. This light held find in the clamps.
A modified and much darker Black and Decker red flashlight that you cannot see the light (yes it is on in the first shot). A good choice to use at a dark site as it will not light up the entire area!
A red light flashlight I got off Amazon and darkened myself. Again you cannot see the red glow and the flashlight is turned on. Another viable option that holds well in the clamps.
Above is the back view of a Agena LED Dual Beam Astronomy Flashlight which held in the holder wonderfully after an adjustment or two to secure it.
My favorite flashlights were the Photon 3 Freedom mini light and my old adjusted Black and Decker light. I like that with the stiff but flexible arm, I can adjust the light exactly where I want it when sitting on my observing chair. I guess I am rather happy with this and I have to state I found another arm that instead of two clips, only has one, and I like that one even better! Hope this helps some of you with how to illuminate your sketching pad at the eyepiece. Remember, not too bright, just enough to see to sketch.