LED / Halogen Comparison

We are often asked, when discussing LEDs in downlights 'What is that an equivalent of in halogen? This is'a difficult question to answer as any generalisation may mislead. Usually one is asking about light output. But in giving that answer, we are neglecting the difference in colour quality that any exchange will create. The other reason why this is a difficult question is that perhaps it shouldn't be asked at all. Just because halogen lamps come in established power doses doen't mean that the corresponding light levels of these lamps are appropriate for the situation in which they are used.

• Colour quality
• Light output
• Comparison chart

Colour quality

If with LEDs you want an equivalent light quality to halogen, you will have to make compromises. That's not to say you won't find an LED with a sufficiently good light colour quality for your project, it just won't be the same as halogen. Halogen has a colour rendering index of 100 %, that's all the colours are represented in the light of a halogen lamp.

Here are two Spectral power graphs for tungsten lamps. The first is a standard graph with three lines representing three possible colour temperatures, the second is a typical graph of a Philips Master ES MR16 tungsten halogen (taken from Philips Halogen Lamp Guide).

As you can see, there is a small output starting at UV-A and the blue wavelengths and increasing sharply to the reds. So warmer colours are better rendered. And cooler colurs not quite so, but the whole visible spectrum is produced.

Below are two graphs that Philips publish for their MasterLED7W GU10(240v). First a 4000k neutral White and then a 3000k Warm White (nearer to halogen).

Firstly, no UV! But there is a lot less power in the warmer wavelengths than halogen.

In many cases, these differences are not important and it would take an A/B comparison for a client to notice if their furnishing was illuminated by one technology or another. Certainly, I would prefer to prepare food under halogen unless LEDs with excellent red output were used. These are rare but do exist. The Xicato Artist range may be suitable, for instance.

Light output

Most comparisons between halogen and LED replacements concern light output. This information is often available in photometric files and manufacturers data. There are two figures that are of interest. One is total lumen output and the other is peak intensity.
Peak intensity is the intensity of the light in the major axis and here we mean the intensity of the light directly under the face of the lamp. With this figure, we can install a lamp in the ceiling and calculate the light level directly underneath on the floor. Some manufacturers have labelled their LED replacement lamps as 'equivalent to 50W halogen' by comparing the peak instensity figures. But unless we are concerned with accent lighting, and in most cases we are not, it is the total light output in all diretions that is more useful. Halogen reflector lamps provide a considerable amount of light outside of their rated beam angle. All this extra light is available inside the space to be lit.

Comparison chart

Below is a table of manufacturers data comparing Halogen (low voltage and mains voltage) and LED MR16 lamps (or integrated fitting with LED lamp).
Please note, with reference to the LED lamps and fittings, these are the higher performance end of the market. Many, if not most, of the cheaper LED offerings have a lower efficacy than the IRC (infrared coated) low voltage halogen lamps and few of the long term advantages.

Lamp or fitting	Description	Power	Light output(Lm)	Peak intensity
Decostar 51	MR16 LV Halogen lamp 38 deg	20W	265lm	518cd
Decostar 51	MR16 LV Halogen lamp 38 deg	35W	516lm	969cd
Decostar 51	MR16 LV Halogen lamp 38 deg	50W	850lm	1780cd
Decostar 51IRC	MR16 LV Halogen IR coated lamp 38 deg	20W	403lm	940cd
Decostar 51IRC	MR16 LV Halogen IR coated lamp 38 deg	35W	1136lm	2134cd
Decostar 51IRC	MR16 LV Halogen IR coated lamp 38 deg	50W	1465lm	2818cd
Twistline	PAR16 MV Halogen lamp WFL	50W	465lm	1122cd
MasterLED 7W GU10	MR16 LED 240V 3000K 25 deg	7W	270lm	1149cd
Halers Evoled	Integrated LED fitting, 3000K, 34 deg	8W	363lm	929cd
Integrale XSM LED*	Integrated fitting	7.1W	489lm	N/A
Integrale XSM LED*	Integrated fitting	10.3W	640lm	N/A
Integrale XSM LED*	Integrated fitting	14.6W	890lm	N/A
LEDMR166	MR16 LED 12V 3000K 38 deg	6W	360lm	N/A
LEDMR168**	MR16 LED 12V 3000K 38 deg	8W	400lm	N/A

* Requires external driver
** Supplied with driver unit

As I mentioned at the beginning, we are used to the available dosages of halogen light and people are asking for the equivalent in LEDs. But should we need so much light anyway? I've seen one installation that uses 50W LV halogen lamps. One half of the room was changed two years ago and new fittings with 35W IRC lamps installed. The original 50W lamps in the other half of the space are still operating but the the reflectors have degraded with age. The owner hadn't noticed the gradual deterioration. One half is now nearly three times as bright as the other but at no point has the owner said that the old area was underlit. Here's a case where the current light levels could be maintained with LED replacements.