Laser Diode, 30pcs Mini Red Laser Diode Laser, 5V 650nm 5mW, Red Dot Laser Head, with Leads Head Outer Diameter 6mm

It's highly unusual for me to write a product review but when I see something like this I feel I need to pass on my experience. What is amazing about this laser is its price. 30 lasers for 43 cents each. And they work well, very well. See the pictures. At 300 feet (91 m) the beam has diverged into an oval about 3" long and 2" wide. Even at this distance, looking into the beam will leave a red spot on your retina for a few minutes. It's very bright even at half power like I'm doing. The modulated beam (20Hz) starts at the boat dock, up to the house, then through the glass door and ending on a wall on the other side of the living room. These lasers also have a limited adjustment for focusing. I plan to use this laser to detect a bird landing on the handrail. When the bird breaks the beam (beam projected down the handrail) it will open a water valve which sprays water down the handrail for several seconds. The logic is done with an Arduino Nano Every. Bird poop is a constant problem, hopefully no more.

I bought these to illuminate a dot on the dashboard of cars parked in my garage. Way better than a tennis ball and string! The lasers have a well defined and focused dot. A couple of the lasers were lower in brightness, but not bad considering the price.Laser diodes are designed to be operated at a specific current. In this case, I estimate 20 mA is about right. The diodes have a 91 ohm resistor in series, so the correct current is obtained by using a 5 volt power supply. Some careful soldering would allow you to bypass the series resistor.The case is made of brass and unscrews at the center once you break free the glue keeping it from turning. The lens is spring loaded against the objective end. The rear end contains the laser diode mounted to a brass heatsink and a PCB containing the + lead and the 91 ohm resistor. The negative lead is attached to a PCB that pushes against the brass heatsink when assembled.Not sure about the lifetime of the laser diode. Lower currents mean longer life. My car park device is on 24/7 so we''ll see.For the fun of it, I took some microphotographs of the diode. The diode itself is way small. In one photo you can see a 0.7 pencil lead.I'm definitely getting my money's worth out of these lasers!

Had 5 (so far) of the 18 I've tested dead or were so dim its not usable. Some have a very wide beam as well, but I only needed a 3' beam distance so it worked ok for my needs.

These are very good lasers. The output is elliptical (maybe 1.5:1) but largely uniform within the beam. Turning the barrel gives a wide range of focus adjustment. The wires are small gauge, so it's easy (for students, anyway) to break the wires off, but they're so inexpensive that replacement isn't heartbreaking. With a 5V input, the lasers are nice and bright.

Used to pay like 1.95 for 2 at electronics store. I was being ripped off. This is a great value, they all work well, bright etc.

Super bargain - Won't return these, but was slightly disappointed to count 27, not 30 as promised. It seems as though there are many vendors selling the 'exact same' item. I tested them all and found that they all produced light, and all of them drew 18 or 19mA at 4.15VDC, except 1 that only drew 14mA (It wasn't as bright).10 of the 27 made a nice tight round dot on my wall 1.5 meter away, the rest were 'okay', less focused, but good enough for many projects. I'm happy because they are useful for many experiments and projects and the price is right. My first project is to affix one to the frame of my home-made gyrocompass such that when the gyro precesses 1/10 degree in either direction, it will shine on 1 of 2 photodiodes, causing my Arduino to tweak a servomotor CW or CCW to relieve the torque in the wiring harness (see Sperry gyrocompass 'phantom' motor/amplifier/sensor from 1943. YouTube Periscope Film #58834. Fascinating).Great bargain.Quality as expected (for the price).

Work great

Previously, I was using the lasers, where were mounted on the circuit board. Fortunately, the project I was working on only needed to have the receiver send a signal the sensor had irradiation or not. This allowed me to used the laser strictly for the beam and reduce the cost tremendously. I found a metal bracket on Amazon that fit the 6mm size perfectly. If you need lasers for a project (school, home escape room, or other needs), I would recommend these lasers. Not one has failed.