Efficiency test for point-source LED

2 min read

NPL is helping Luminanz test the efficiency of a lighting concept that is 70 per cent more energy efficient than existing light bulbs.

An LED light fixture that diffuses like a normal bulb but directs beams only in areas where illumination is needed could brighten homes and businesses in the future.

The technology is being developed by Luminanz, a Bolton-based LED lighting company. The developers believe the new lighting concept - dubbed LED Luminaire - will be an energy-efficient replacement to current light bulbs and last 50 times longer.

It is claimed that the UK's carbon footprint could be cut by 43,000 tons a year if the technology were installed in just one million homes.

The Luminanz technology combines a light bulb and fitting into a single unit, which means the lighting would be sold within new fixtures.

In commercial settings, where lights are turned on all day, the upfront costs of buying new fixtures would be insignificant compared to the amount saved by not constantly replacing light bulbs, said Paul Miller, a research scientist at the National Physical Laboratory (NPL), which is testing efficiency of the lighting.

‘As people become used to the technology they will start to take on board the advantages of changing a light fitting once and [it lasting] 10 years,’ he said.

After these 10 years, he added, it would be possible to buy a replacement light source.

Miller said that the new lighting concept is based around a white LED point-source and Luminanz-developed waveguide technology. The waveguides change the direction of the point-source light into something that resembles the kind of lighting most people are used to.

In order for the new type of lighting to be sold on the market, it has to prove it can meet certain markers. The challenge, he said, is that traditional measurements for lighting cannot be applied to Luminanz’s new concept.

‘If you use the same instrument you use to measure incandescent light bulbs you can get incorrect answers.' 

For this particular measurement work, the NPL is relying on a goniophotometer. Developed at NPL, the goniophotometer measures the directional light distribution of lighting fittings, comprising a 2m rotating mirror and a detector that is mounted 18m away from the light source.

‘A light from the lamp hits the mirror and the mirror moves with respect to the source,’ Miller added.

‘By measuring the light around every angle of the source we can build up a picture of where the light’s going. Also, we can add all of those numbers up to produce the total amount of light that comes from the light source.’

The numbers, together with electrical measurements of the light source, will tell how much light is produced per watt of electricity . The direction of the light will also indicate its task efficacy because any light that illuminates unused areas is wasted.

‘For example, when you have a street light, any light that goes up[wards] is wasted light,’ he said.

The intensity and colour of the light is also an important consideration. ‘You might recognise that this in an office and you’re trying to work at your keyboard [but] it’s just too bright,’ Miller added.

The NPL is providing these measurements in a format that Luminanz’s lighting designers can plug into software and determine the amount of light that shines in 360o of space. If adjustments are needed, the fitting's design can be changed to meet the necessary specifications.

Miller said the Luminanz light concept is beginning trials in markets where the maintenance of lighting is both expensive and safety critical. He added that when the trials are completed, the lighting is likely to be targeted at the commercial sector before the domestic market.

Siobhan Wagner