Light Output

High output LED fittings in a 15th Century barnHistorically we used to get a sense of light output by measuring the amount of power that went in e.g. if you used a 50w mains halogen lamp the amount of light produced was pretty consistent and ‘50w’ gave you an idea of what sort of light should come out.

With LED this is very different. LED chips vary hugely in output, even within the LEDs produced by one manufacturer. One of the very reputable chip manufacturers, Cree, produces 1w LEDs in a choice of 40, 60 or 90 lumens. The performance and price difference is huge.

The optical design of the fitting then has a significant impact on the actual amount of light delivered; good optical design using high quality materials can ensure that up to 90% of the light generated is used, and it can be directed to the desired location. Bad optical design and poor materials can absorb 50% of the light produced. Beware, some manufacturers claim lumen values which are measured before these losses. 

Measures of light you may come across

Lumens
In simple terms, the amount of light given out by a light source in a defined beam or angle. This makes lumens the easiest measure to relate LED output back to traditional GLS and Halogen lamps.

Lux
A measure of the amount of light falling on a surface. It equals 1 lumen per square metre. Lux is affected by distance from the light source and beam width: a fitting with a narrower beam will deliver a higher lux value over a smaller area than a fitting with the same lumen output but a broader beam width.

In our own projects we use dedicated fittings which have fabulous performance and efficiency so if required they really are comparable in output to halogen lamps. The LED retrofit lamps we use are the best available on the market.

One of the common complaints we hear about LED lighting is that it can be "dingy".  That's often not a function of colour.  It's usually down to specifying a source that doesn't give the output that's needed.  It’s important that you look at the delivered lumens output from an LED fitting or a retrofit LED lamp, decide a short list of potential fittings/lamps and ideally test them out vs. traditional sources. 

 

 

HIgh output floor-recessed LED uplight

Checklist when testing light output

  • Check the ‘delivered lumens’ output for a better comparison.
  • Even better, test the LED fitting or lamp in a side-by-side comparison vs a halogen lamp. If testing a downlight, use a 50w low voltage (12v) halogen lamp as a comparative benchmark.  

The lamps or fittings you are comparing should have similar beam widths otherwise this will distort your conclusions.

Output in Lumens from “traditional” sources
35w low voltage (12v) halogen spot c.550 - 600
50w GU10 mains voltage halogen spot c.600
50w low voltage (12v) halogen spot c.800-950
40w GLS incandescent candle lamp c.450
60w GLS incandescent candle lamp c.750

Download The Lighting Buyer's Technical Reference Guide

A primer to specifying and designing with LED lighting