LED/Halogen Lamp comparison (Feb 2008)

Like many, I have been interested in changing my Halogen lighting for the much raved about LED units claiming huge lifespans and 90% energy saving.

I bought some of these units and this is what I found.....

Lab Test - 1.

This test has been carried out using Logit Voyager datalogging unit with a Smarteye light sensor.

The absolute accuracy of this unit is not relevant here as a simple comparison test was carried out and the difference in light output was such that even quite large errors would not have any effect on the conclusions made.

Each lamp was attached to a regulated power supply (12V DC +/- 0.1V).

Each reading was made 1000mm from the front of each lamp.

The angle off-axis was measured using an ordinary protractor, so can expect an error of +/- 2 degrees.

The measurements were taken with 0 degrees off-axis in the vertical and 0 - 100 degrees (20 degree increments) in the horizontal.

Background light: 22 lux.

Results (average of three sets of readings):

This first chart show that the very high comparative on-axis output of the 20W halogen unit makes the rest of the data hard to see.

The chart below shows the rest of the off-axis data more clearly.

I fully accept that these results are only a guide and not a definitive test, but the results show how far off the LED unit is from coming even close to the halogen's output.

To take into account the two different beam angles you could average out the results at different angles off-axis:

20W Halogen Spot Average: 3051 lux

2W LED Flood Average: 431 lux

Even if we take out the very high on-axis Halogen reading to try and give the LED a chance:

20W Halogen Spot Average: 571 lux

2W LED Flood Average: 231 lux

However we look at this, the LED unit tested here has a light output which is not even close to that of a 20W halogen unit.

Even at 100 degrees off-axis the halogen spot has rough 7x the light output.

LED lighting is improving every day, is very economical to run and clearly sound environmentally friendly technology.

This test shows the importance of being very cautious of claims about LED brightness. The unit here was claimed to have a brightness similar to a 27W halogen unit. However we try and allow for different beam angles, this is not even remotely close.

Simplified test with photos - 2.

The above test was done at work in a laboratory.

The test below was done at home and is not carried out using proper controls, or accurate distance/angle measurements, but the difference in brightness of the two lamps is so large that even with multiple errors the conclusion would not be any different.

1. Here is the light meter I used:

2. It is important that the voltage is correct and the same for both lamps. Rather than a picture of the power supply, I have done better. The photo below shows the actual voltage in a light fitting carrying both bulbs. 11.99 Volts is about as close to 12.00V as you can get!

And now for some quick and simple tests to compare the light output of the LED and Halogen lamps....

In this picture I have put the meter a long way off-axis. This is for two reasons. First, the LED lamp is not a spot but a wide angle flood, so this makes the test fairer. Second, if I point the meter at the lamp's 0 axis at this close range (to allow photos), the meter overloads and errors.

The reading is just visible at 17,835 Lux. Notice how I have the meter outside the normal spot light angle.

This is not a proper experiment like that with the data at the start of this page. So I will try and give the LED a extra chance by pointing the meter straight at the LED lamp to get the maximum reading possible. You can see this in the next photo.

With the meter pointing straight at the LED lamp the reading is 3755 Lux. Of course if I were to put the meter at the same wide angle as for the halogen lamp it would be less than this.

The halogen bulb used is shown below:

The beam type of this halogen lamp is not important in this simple comparison because I took the reading at a wide angle and the readings between the two lamps so large that the result cannot be disputed.

Over 17,000 Lux for the halogen at a wide angle compared to just under 4,000 Lux for the LED straight on.

Conclusion - unless you go for expensive Luxeon type LED units - do not expect any LEDs you buy to match your existing halogen units.

(Please note - these tests were carried out Feb 2008 - LED technology is improving all the time).