OPINION
When is an LED equivalent to a halogen?

Neil Knowles doubts that PhotonStar’s CeilingStar LED downlight has an output equivalent to that of a 50W MR16 lamp. Fenella Frost from PhotonStar responds

In the September issue of Lux magazine, Neil Knowles pointed out that a 50W MR16 ES lamp can produce 1,180 lumens and thus he concluded that our equivalence claims for the Saint Michael’s Hotel project were incorrect.

Although his statement about the lamp is in some circumstances correct, it does not state the beam angle at which this is relevant and, more importantly, the lamp he mentions is not the lamp that we replaced in the hotel. Our claims of equivalence are based on Celma-published data for industry standard halogen lamps (rather than manufacturers’ figures for the higher performance eco-halogen type mentioned in the letter) and take into account the utilisation factor and useful/delivered lumens rather than source lumens.

It is always tricky when you compare one-for-one direct replacement products – it is much better to review a complete overall project.

Calculating equivalence between non-directional sources such as incandescent and directional sources such as LED cannot be done using initial lumens. For halogen lamps, our calculation was determined using the delivered hot lumen package taking into account the LOR from the complete LED luminaire. The delivered output is equal or superior to the flux of the halogen lamp without an equivalent luminaire in the forward 90-degree cone. Celma’s published figures for comparison state that a 50W MR16 delivers 600 lumens in the 90-degree cone.

We recognise that some of the leading halogen lamp manufacturers supply better technology that exceeds these figures. This is why we developed our Venus 1,000-lumen light engine that typically delivers more than 900 lumens (hot lumens within luminaire) from our Laser luminaire, and matches the performance of some of these higher specification lamps (in a luminaire) when it is required.

The case study was a mix of new and retrofit. The lux levels with industry standard 50W MR16 lamps were measured before the retrofit, and again after installation of the luminaires – showing slightly higher lux levels at the working plane with the CeilingStars.

We are aware that some less scrupulous LED manufacturers use ‘hero numbers’ based on source lumens, cold lumens, narrow beam angles and high CCTs, or don’t state that they are comparing with GU10s. PhotonStar has a reputation for supplying full performance data for every beam/CCT variation that is realised post installation.

The benchtest of leading halogen replacements in Lux in November 2010 supports this claim, as do the many post installation testimonials.

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