I need to make an Arduino based setup where an LED's intensity is varied, and the variation should be between 50Lux and 500Lux.
The LED needs to RGBW, where user can chose between any color.
I need suggestions on how to do it. What parts I would need and how this would be executed.
Step 1
Source a suitable LED
How?
That's what I would like to know, how to know which LED is suitable? In my location there is only one kind of RGB LED available (I am planning to make white by lighting all of them at the same time).
How to know how much would its intensity be at a distance of say 350 millimeter.
Maybe using a Pot?
Start by “playing’ with a dimming standard LED so you learn about the idiosyncrasies of PWM and LEDs.
Then you’ll know a lot more to work with your preferred RGB part.
Are the colorimetry and brightness critical, because that’ll be trickier to get exactly right.
This is one of common issue on LED. Different color, manufacture or production batch may also have this issue. It caused by the VA curve of the LED. You can use a two channel oscillioscope to identify the differnce easily.
Current limit resistor connected in series with LED is a fixed current limitor and it does not help on this issue.
The posible solution may be a constant current source connected to EACH LED pin.
This You Tube link may give you some know-how of a current source.
Two Simple Adjustable Current Source Circuit Designs
Good luck.
nope, I was hoping to use a sensor with the arduino nano to measure intensity of light.
Design and code a LedDimClass simply.
Arduino has a built-in example of controlling an RGB LED. Here is an implementation of the code in the Wokwi simulator:
There are a few more examples here:
You can use your smartphone to measure lux. There are different app available depending on what you have.
Isn't lux a measure of the illumination of a surface?
With samsung phones it is named Sensors and may be already installed...
500 lux is pretty bright...
You will probably need a led strip or some power led to reach that kind of brightness.
Or some reflector to concentrate the light...
500 lux = 0.7W/m2
A stadard led uses 0.02AĂ—2V=0.04W.
And conversion efficiency from electric to light is not 100%...
Yeah.. I'm not a photographer so I don't have a feel for Lux but you're going to need "high power" LED.
The brightness/light output from regular little LEDs are normally specified as millicandela (mcd). I found a Lux to Candela calculator
And Lux (the amount of illumination) depends on how close you are to the light source. If you are close and lighting-up a smaller area, of course you can get-away with a smaller, lower-power LED.
Or as build-1971 says, an LED strip (multiple LEDs).
High power LEDs are normally driven from a special constant-current power supply (or a variable current supply for dimming).
Regular power supplies (or drivers) are constant voltage and the current depends on the load. But LEDs are "current driven" so a constant/controlled current is supplied and the voltage "falls into place". With regular little LEDs a resistor is used to control-limit current. Although that can be done with higher power LEDs, it's inefficient and you need a high-power resistor to go with the high-power LED.
Some constant current power supplies allow for PWM dimming which is "easy" with an Arduino. Except that the "industry standard" is 10V PWM so you may need a little transistor circuit to boost the Arduino's 5V (or 3.3V) output.
With RGB, you'll need one power supply (or driver) for each color.
Note that bare high-power LEDs need heatsinks.
If you can use an LED strip, addressable LED strips have a built-in driver for every LED so all you need is an Arduino and a power supply for the LED strip . In this case, a regular-old constant-voltage power supply. The software is a bit complicated (because every LED can be addressed/controlled individually) but most of it is handled by a software library.
