Lights Testing

Temperature

The LEDs used for the lights can get very hot very quickly. It is important that the temperature of the lights stays within limits that will not interfere with the functionality of any nearby circuits, and will not pose a safety hazard.

The graphs below represent the temperature of the light board over time. All trials were performed with 12V supply. Duty cycle was set to 100%.

Red Lights: back

Temperature appears to be unstable throughout the trial, this is because the temperature probe came off of the board. Temperature at the end is somewhat more stable. Temperature stabilized to around 66 degrees.

The power supply drew 0.43 A of current (5.16 W).

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Red Lights: front

Temperature stabilized to around 68 degrees.

The power supply drew 0.43 A of current (5.16 W).

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White lights: back

Temperature stabilized to 79 degrees.

The power supply drew 0.59 A of current (7.08 W).

White lights: front

Temperature stabilized to about 90 degrees.

The power supply drew 0.59 A of current (7.08 W).

Voltage Boost

Since a boost converter is used in the driver board, a boost in output voltage is expected.

Voltage boost changes depending on PWM duty cycle (which can be adjusted with the potentiometer).

Here are the results for voltage boost and supply current as a function of duty cycle. The power supply was set to 12 V.

Burnt out LED

When a single LED was removed, the remaining LEDs were fully illuminated at approximately 3V. Constant current mode was activated on the power supply. Supplied current was 250mA.

Brightness

Brightness was measured in a dark room with a photometer. The LEDs were driven directly at 12V, without the driver (they burnt out in an accident, guess who did it). What was the current limit of the LEDs when doing these tests?

This website was used to convert from lux to candela:

https://www.rapidtables.com/calc/light/lux-to-candela-calculator.html

Amber reference lights:

60 lux from 1 foot = 5.6 cd
the ruler that was used was slightly reflective.

Red lights:

12 V * 0.21 A = 2.52 W
850 lux from 1 foot = 78.9 cd
This circuit included the zener diodes used for protection.
the ruler that was used was slightly reflective.

Further Brightness Testing

Further lights testing was conducted by Micah Black.

Things to keep in mind while testing:

The lights and the light meter have different spectral responses - that means that the light meter will not pick up all of the light produced at different wavelengths.

The light meter that was used was purchased here: https://www.amazon.ca/Dr-Meter-Digital-Light-Meter-Illuminance/dp/B005A0ETXY

Spectral Sensitivity of meter:

Spectral Power of lights (cool white, amber, and red are used for the car):

So we have to manually apply a correction factor based on the amount of measured light and the frequency that it is at.

Test Setup:

Test Results:

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Test Summary:

Light Output

*This was measured very low, but it seemed just as bright as the other colors to the eye. The erroneous value can probably be attributed to the spectral power of the led not matching the datasheet, and/or the spectral sensitivity of the meter. This was manually corrected for the red LEDs.

For reference, the values that we measured were slightly higher than what was given in the LEDs datasheet. The LED datasheet gives a minimum value, so the measured values can be somewhat trusted.

The temperature affects the lumen output a fair bit, much more noticeably with Amber lights. If I had read the datasheet fully before jumping in to the tests, then I would have realized why:

These results guided the decisions for the number of LEDs and the drive current to use for each lights board. The decisions can be found on the Details of Lights Boards page.