Introduction: 15 Watt LED Helmet Light With Wide Angle Rear Light

About: Autistic person who's interests include utility cycling, recreational cycling, cycling safety, electronics, gardening, Arduino, and LEDs.

This helmet light produces a maximum of 1300 lumens for its headlight and a maximum of 400 lumens for its rear light. It has different modes for different conditions such as day time and night time. It can last between seven and eight hours for daytime visibility, and between one and two hours at full power. It also has solid modes which may be useful if you want to use it as a headlamp.

Step 1: Materials

3 - red LEDs with 10mm base pad (they should be low footprint)

3 - neutral white Cree XP-G2 LEDs

3 - Cree XPG LED lenses

3 - 10mm elliptical beam optics

4 - LiFePO4 18650 cells

4 cell 18650 battery holder

3A fuse

Fuse holder

Aluminum bar

Aluminum heatsink


Velcro straps

Plastic strips

Clear plastic (such as Plexiglass)




Cable ties


1500 mA LED driver

700 mA LED driver

For electronic components, see the BOM

Step 2: Microcontroller Circuit Board

This circuit has a microcontroller for PWM dimming the front and rear lights (W1 and W2), reading the switch, reading the battery voltage, and enabling or disabling the LED drivers (W3). Two LED drivers are needed for both lights. You can build the LED driver from scratch.

It's also possible to use pre-made drivers which can be ordered online from eBay and LEDSupply. For pre-made drivers, you may need to modify the microcontroller's circuit board to use them. They may not have a pin for sleep mode.

Step 3: Microcontroller Code

Upload the code to the ATtiny85 microcontroller.

The helmet light has daytime, night time, and other modes. Its modes were divided into three groups because it saves time cycling through them when adjusting power levels. Sometimes, you'll need a lower setting because the light can be blinding at high power levels.

The daytime modes have shorter pulses which keep you visible in the day time and prolongs the battery life. The night time modes have inverted pulses which alert drivers of your presence and and lets you see properly. There are three different power levels for night time use. The program has other modes such as solid red, solid white, and power saving. The solid modes can be useful for reading a map. The power saving mode keeps you visible before the battery runs out and it's also triggered when the battery is low.

If you want, you can modify the code's low battery indicator's trip voltage, strobe patterns, and PWM pin numbers. There might be a strobe pattern that appears brighter with less power than those in the program.

Step 4: Possible Options

For this Instructable, I used the 15 watt option with three 5 watt LEDs.

You may use other options for higher lumens or lower weight and size of the setup. Higher lumens would be useful at higher speeds. Using two LEDs instead of three would reduce the footprint of the headlight and allow you to use fewer cells. It's also possible to reduce the footprint by using a Cree 3-Up LED which has three LED chips per board instead of one per board. They're similar in dimensions.

The custom LED driver was designed to handle 2A. If you want to use 10 watt LEDs, you'll need a 3A LED driver which requires using different values for some of its components. You can use a 2A inductor and replace the 2A Schottky diode with a 5A diode.

If stable brightness throughout the battery's state of charge is important, the battery voltage needs to be higher than the LED forward voltages and the driver's dropout voltage combined. The recommended minimum battery voltages were calculated based on the maximum forward voltages of the LEDs and the dropout voltage of LED drivers which may be 1.5V. The red LEDs may be up to 2.8V each and the white LEDs 3.2V each.

I measured the Luxeon Rebels to be around 2V at 350 mA and 2.1V at 700 mA. If you have similar measurements, you should be able to use a battery voltage of 8.4V when using two white LEDs. 7 NiMH cells should work. If a different battery voltage is used, you may need to modify the low battery indicator's trip voltage.

I recommend safer battery chemistries such as LiFePO4 or NiMH cells because they'll be installed on you helmet.

10 watt using two 5 watt LEDs

  • Minimum battery voltage: 9.9V (can use 3 LiFePO4 cells or 9 NiMH cells)
  • 2 Cree XPG/XPG-2 LEDs

15 watt using three 5 watt LEDs

  • Minimum battery voltage: 11.1V (can use 4 LiFePO4 cells or 10 NiMH cells)
  • 3 Cree XPG/XPG-2 LEDs

20 watt using two 10 watt LEDs

  • Minimum battery voltage: 9.9V (can use 3 LiFePO4 cells or 9 NiMH cells)
  • 2 Cree XM-L2/XP-L LEDs

30 watt using three 10 watt LEDs

  • Minimum battery voltage: 11.1V (can use 4 LiFePO4 cells or 10 NiMH cells)
  • 2 Cree XM-L2/XP-L LEDs

Another way of increase the lumens is using a higher battery voltage and more LEDs in series. You might be able to use nine cells and 8 white LEDs in series for an 80 watt headlight. With 1150 lumen Cree XPL LEDs, the total lumen output can reach 9200 lumens! You can increase light output by using LEDs in parallel which require one driver per string. It's also possible to increase their lumens per watt by underdriving them. Make sure that your components can handle the voltage.

Step 5: Install Circuit Board Into Enclosure

A 2-cell 26650 battery holder was used for the microcontroller and LED driver modules. Since there're no standoffs that are a few millimetres high, I used plastic washers instead.

A place for the switch could be the exterior of the enclosure

The 18650 cells were external. I soldered a fuse close to a 4-cell 18650 battery holder.

Step 6: Assemble Front Heatsink

For improved heat dissipation, you can attach heatsinks to the aluminum bar. Thermal paste can improve heat transfer. You may need to make threads on the heatsinks with an M3 tap because there's not enough space for the nuts between their fins. Make sure that they are is cleaned between their fins.

Step 7: Assemble Rear Heatsink

Assemble the heatsink so that there's space for the rear facing LED and the two 45 degree facing LEDs. The bar for the side facing LEDs should levelled. You can use a #6-32 tap to make threads for the bar that holds the side facing LEDs.

Step 8: Install LEDs Onto Heatsinks

Attach the LEDs to the heatsink with epoxy. Make sure that they are lined up if you're using elliptical lenses. Once set, solder their wires. I used hot glue to attach their lenses. Only glue the legs or lens holder of the lenses. If the hot glue touches the part of the lenses that internally reflects light, some of the light will leak out. If that happens, you can use a small amount of rubbing alcohol to separate it. Only use it where it's needed.

Step 9: Install Plastic Covers for the LEDs

The acrylic was cut by scoring. Once cut, drill the plastic and dull the edges with a file.

Step 10: Assemble Self Levelling Bracket for the Rear Light

Attach the rear light to a 3" screw with cable ties. Use nuts and washers. This allows the light to level. For long distance visibility, the light should aim straight. Limit its range of motion with a cable tie above it. If the light easily gets stuck, you can try trimming part of the plastic.

Step 11: Helmet Light Installed

Attach the headlight and rear light to the helmet with cable ties. The headlight may need some foam and four cable ties for proper aiming. Level the rear light horizontally.

Attach the battery and electronics enclosure with two Velcro strips perpendicular to each other. They should be in plastic bags for water resistance.

If you have a helmet camera, you can prevent the light from reflecting into your camera by blocking it with black tape.

Step 12: Ride Safely

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