Newbie Questions (sorry!): Powering/regulating output of 5mm LEDs (UV, green, blue)

Hello everyone,

This is my first post so please bear with me! I did a quick search but figured I'd ask my question since I couldn't find exactly what I'm looking for. I know these are very newbie question... I work in a biology laboratory and I'm trying to build a setup to look at the behavioral response of insects to specific light (UV, visible, green, blue). It will essentially be a T (or Y) maze where the insect is loaded at the base of the tube apparatus and then must choose to go either right or left depending on the preference for the light (one 5mm LED at the end of each arm of the T/Y). There are TONS of 5mm LEDs from various manufactures. Can you recommend some that will be the most stable in terms of output and wavelength from one experiment to the other? In addition, I need to control the output of each LED (dim/brighten). There are potentiators but I'm not very familiar with the electronics behind everything. So any help there would be greatly appreciated. Any finally, what can I use to measure the light output of each LED? Any links to products would be great for all the above. Again, thanks for the help!

Cree makes the best blue and green 5mm LEDs. They are the best bang for the buck for price, performance, longevity and availability. Stay far away from that ebay junk. UV LEDs are available in specific wavelength bands. Depends on what you want.

You can power the LEDs with 5 volt supply and potentiometer to adjust light level. You still need resistor ahead of the pot so the LED isn't burned when the pot is full open. Accurately measuring the intensity of a given wavelength of light will need costly equipment. Would the university have such a device?

1st. Where are you located?
2nd. I would just go with a small custom built plcc6 RGB+UV setup with standard 44 key remote and controller. Uses pwm control for brightness and can control each color independently or together.
3rd. I build things like this all the time and would be happy to help you.

Oh yeah,.... :welcome: !!!

> pwm
that's "pulse width modulation" and will introduce an issue for biology work with visual systems if used; "flicker frequency" is the search term.

But you can put "neutral density" filters in the system to change how bright it appears: https://www.rosco.com/filters/ecolour.cfm?DisplayType=30
(find a photography or theatrical supplier and ask them for a free "swatch book" with samples, cut'em up)

Yes, filters would work for all but uv. Most gel filters will hinder the uv spectrum unless you use woods glass, and that gets pricy.
A variable currant driver would work as well, as opposed to pwm.

Thanks for the replies everyone. I definitely can't do PWM since I don't want to introduce an extra variable (flicker) into the experiment. I had thought about ND filters but I was thinking of going the potentiometer route since it SEEMS fairly straight forward. I found this online:

http://www.instructables.com/id/How-to-control-the-brightness-of-a-LED/

I've never even heard of a breadboard but I think I'll be picking a few up and building one of the above for each LED. Should I go with the recommended resistors (one 250 and one 1k) or any other suggestions?

JohnR66: As far as 5mm LEDs, I was looking at these: http://www.ledsupply.com/ultra-violet-5mm-leds You mentioned Crees, though. Do you have a reputable dealer where I can order from? Or maybe if there is a dealer local to me (I'm in Pasadena, CA).

The university may have some equipment that I can use to measure intensity but I'll have to dig around. I was just wondering if there were any not TOO costly instruments for doing so.

Thanks again for the input everyone!

I agree PWM is not a good idea for this experiment. The instructables video is okay but the breadboard is more useful for experimenting than project building. Once you pin down the right values, you should solder together a circuit rather than running an experiment using breadboarded circuits. That would remove the breadboard as a potential variable in your experiment.

There are some cheap Lux meters available on eBay, but they will give only a relative measurement. Accurate measurements at different spectral content requires expensive equipment.

Digikey and Mouser sell Cree LEDs. Radio Shack seems to source their LEDs from a decent supplier. They are not as bright as Cree and are more expensive. RS has resistors, breadboards, potentiomenters, voltage regulators and probably other things you need for the circuit. They carry a UV LED that that is around 400nm. If you pay the shipping I can send you a sampling of Cree blue and green 5mm LEDs. PM me.

If you wish to use different colored gels ( thin flexible acetates), Rosco has a huge selection of colors to choose from, so does Cokin, Tiffen etc. I got a swatch sampler from Rosco for around 5 dollars and the gels are about the size of 2" X 3" purchased from B&H photo. You can actually get way over a million different colors by mixing them. I put them over my leds to add color effects to my background in tabletop video/photo commercial work. I tape them over a white light source , led flashlight/led video light, for example.

Thanks for the help everyone! I was able to build the breadboard circuit and also have the appropriate LEDs and everything works as expected. Now though, I'd like to build a more "permanent" circuit and make it look a little more professional. The breadboard is nice but it's a little annoying have wires everywhere. Would I just need a PCB and then copy the breadboard connections onto it? Also, I would like to be able to monitor the voltage (which would give me a relative brightness of the LED) so that I can incrementally adjust the brightness of each LED. Most voltage LCDs that I've seen online have a minimum measurement of 3.5V. I'm hoping to go lower in my setup. Any suggestions? I've never done any circuit building so again, sorry for the newbie questions! And thanks in advance

The meters you are looking at are battery meters for cars. They are unusual in that they are designed to be run off the voltage they are measuring, which allows them to have only two wires, and also is why they can't measure below several volts. You want to look for panel meters. You will get more general-purpose meters that go down to zero, and some even measure negative voltages too. They will have a separate supply from the voltage they are measuring. Most LCD versions can be run off a 9V battery.

This is one example: http://www.mpja.com/3-1_2-Digit-LCD-Panel-Meter-PM128/productinfo/6929 ME/

Actually though, the brightness is much more closely related to the current through the LED than the voltage across it. That's what you should be measuring.

If you want to measure current, you run it through a resistor and measure the voltage across it. This is how most digital multimeters do it. Place a 1 ohm resistor in series with the LED, and the meter I mentioned, hooked across the resistor, will give the current in milliamps, up to 199.9 mA. That's because the meter in it's basic configuration is set up to measure 0-199.9 mV, and 1mA through a 1 ohm resistor gives 1mV, so the readout is directly in mA. There are lots of meters around that are set up with this same configuration.

As far as the circuit board, it's a great idea if you want to make more than a few, and/or if you really want it to look nice. If you're clever and willing to put in the time, it's actually quite possible to design your own online, and have some made for reasonable prices. AFAIK, all the online layout packages tie you to the board maker, and they aren't the low, low, lowest prices.

If you want really cheap, use a free software package and buy boards from some place like seeedstudio.com. My last order from them was 10 each of 2 different boards, and the total order with shipping was $56. They don't offer an online layout package, but you'll be hard pressed to beat their prices for boards. They make it especially easy to order from them if you use the free Eagle package.

The online layout packages may be easier to learn than the free downloads, but I don't really know. I've had access to professional packages since I started.

Just google "free pbc layout" and you'll wish you had a few more hours in your day.