Thursday, September 27, 2012

diy testing of led lamps

I had done some testing of LED lamps available to me to rank them for brightness and efficiency. I went through several interations of a DIY test method to help me select a lamp for my 1 watt DIY garden lamp project. Here is a part of the assortment that I tested back in February. I have a few more I'd like to try so this is ongoing.

I wouldn't normally do this for just one lamp, but the idea is to create a prototype for something that could be reproduced on a limited "craft" scale as a DIY project. Perhaps a dozen or so to surround a garden or guide a walkway? Or even a hundred?

My goal of making the maximum attractive light from only 1 watt of power is arbitrary. 1 Watt is an impressively sounding small number but it could be any amount. As it turns out, 1 watt can produce a very impressive amount of light as we have all seen. I will describe a simple but effective test method that helped me rank them.

You can modify this any way that makes sense to you. It does not become dangerous until you start looking at the line voltage 110/220 operated bulbs. I don't think you need to involve line voltage in powering an outdoor system except where it plugs in to keep it safe - so all of the LEDs I tested were of the "12 volt DC", automotive or flashlight type.

I had gathered LEDs from various sources and I wanted to be able to compare them in some semi-organized fashion. I wanted to be able to measure the amount of light produced and the power used by each one. I wanted to observe the light they produced in as objective a manner as possible, but simply.

click any pic to enlarge

There is a bit of basic electronics and physics involved but it is pretty easy stuff. The equipment you can usually borrow or get used what you need at low cost. You don't need it very long, just for the tests. This is a schematic of my LED test setup. The variable power supply allowed me to vary the electrical input to the LED in a smooth manner. I don't say whether it is AC or DC since either could be used. I'll talk more about that later.

Two of the meters allow me to measure the VOLTAGE and CURRENT flowing in the circuit loop, through the LED and back to the supply. From the voltage and current, I can calculate the POWER (the watts) used by the LED. With a ideal variable supply, I can vary either the voltage or the current or both.

The lightmeter lets me measure the light produced. There are different types of light meters and I will talk a bit about that. I was lucky to have a very nice old instrument from Tektronix called the J16 that allowed me to measure either foot-lamberts or mW/

This is the actual test setup. I took this picture in the daytime but daylight through the window affected the tests, particularly when I used the ft-lambert sensor so all of my later testing was done in the dark. The cardboard box is around the J16 lightmeter and the variable supply and the meters are to the right.

You will see that the LED I am testing is mounted on a little frame above the J16 and both of them "look" the same way, towards a bright white sheet of paper taped to the wall in front of them, inside the cardboard light box. In the first pic above, you will see a number of LEDs mounted in these frames. I made them out of scrap wood, all the same size (about 15x8cm)so that they would clip onto the J16 easily and could be swapped around. I tried to mount the LEDs (which were all shapes and sizes) so that the main emitting surface was about level with the surface of the frame and mounted at its center.

In this way, I tried to have a similar environment for all of the LEDs. The LED and light meter are about 55cm from the white paper which is tabloid or north america B size paper. It is what I had available. You can use whatever size of sheet and setup that makes sense for you, but the idea is to keep it the same for all of the LEDs as much as possible.

Thank you for your interest.

George Plhak

diy landscape lamp reading list
a very bright 1 watt diy led garden light
making a lamp from a 2x4
best light at least cost - about testing bright diy leds at home
diy testing of led lamps - this article
diy 1 watt led update
diy garden lamp progress
a shielded low power diy garden lamp

Related: Fixing LED Strings (Christmas Lights)

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