need to illuminate some digits to see at night

[jon5500]

I have a variable power control that I built for an electric blanket. The control itself has a variable resistor in the top of the case and, for simplicity, I just marked the top of the metal case at various points with a permanent magic marker signifying different power levels as the variable resistor is turned. However, the only way to see the adjustment is by turning on the room light at night and since this awakens me a bit, I need to find a better way.

At first I was looking at some of that fluorescent paint that is first illuminated under normal room lighting for a period of time to charge it and then supposedly it glows throughout the night, but I can't seem to find any cheap paint with 8 hour+ specs.

Any thoughts would be welcome here and thanks in advance.

 

[Alec_t]

Welcome to EP!
Could you perhaps have a series of raised marks (e.g. blobs of hot glue) to indicate position by feel rather than sight?

 

[jon5500]

Thanks. I actually found some fluorescent paint and tried it out today after painting over the digits. Although illumination is quite bright initially, after about 3 hours it has faded to the point where I'd have to turn on the light. Could be that the paint is too old, but not going to shell out for new at this point. So, in my junk box, I found a couple of LED's. I have a red one temporarily mounted in such a way that if it works, I can just glue it to the top of the chassis tomorrow. I can add another red at another section if the single one isn't enough.

 

[Harald Kapp]

How about a UV LED to illuminate the fluorescent paint without being visible to the naked eye? See e.g. this thread.

 

[jon5500]

How about a UV LED to illuminate the fluorescent paint without being visible to the naked eye? See e.g. this thread.

Interesting idea, but I'm not sure I trust the safety of UV enough to try it. UV light can be harmful to the eyes. Normally, the shortest wavelengths cause the most trouble, but there can be enough leakage from longer wavelength lights to cause concern. The red LED I used last night worked fine. I may place one other one to slightly better illuminate the numbers, and call it a day.

 

[Harald Kapp]

UV light can be harmful to the eyes.

Definitely.
But you need only a very low intensity to make the paint glow in the dark.
However, if you're satidfied with the red LED there's no reason to forage into UV territory.

 

[jon5500]

Since I haven't yet glued down the red LEDs, I'm going to give this UV suggestion a try. I found some LEDs of longer wavelength and some blacklight pigment to mix with a medium. They may work with the glow in the dark paint I already used, but if not the pigment definitely will.

 

[Harald Kapp]

I found some LEDs of longer wavelength

UV would be shorter wavelength.

 

[jon5500]

UV would be shorter wavelength.

In the spectrum of light and just above or below, yes, UV is the shortest wavelength of light/ near light, but I was talking about within the UV spectrum itself- UVA, UVB, and UVC. Sorry I didn't clarify better.

 

[jon5500]

Update on this: The UV diodes arrived two days back and they are working great for the illumination. The blacklight powder I also ordered, to mix with an existing paint, still hasn't arrived, but the diodes are causing enough fluorescence in the existing "glow in the dark" paint I used originally that the new powder actually isn't needed. Thanks again for the info on this, Harald.