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LED Retrofit lamps versus integrated luminaires

The technology of Light-Emitting Diodes is increasingly replacing conventional bulbs in public and industrial lighting systems. When replacing an HQL bulb of small to medium power (50W - 150W) the choice is often between: LED retrofit bulb or complete LED luminaire. The lower price and the fact that it is much easier to retrofit an LED often speak in favour of this option, although there are always those who are critical of retrofit technology and who put forward well-founded reservations, yet in many cases also merely cling to prejudices that exist as a result of good lobbying. This article deals with the advantages and disadvantages of retrofit technology, and is intended to help you take a more objective decision as to where this approach makes sense and where not.

1) Service life and temperature
The concept of "service life" in connection with LED lights and bulbs is, in positive terms, probably subject to the widest range of interpretation as far as relevant parameters go. Not only on the part of suppliers, but also by customers. The "service life" often lists details such as 50,000 hours, 100,000 hours or even longer, without any explanation of what this means. The expectation that arises here often bears no relation to the actual output of the complete product. This figure almost always specifies the time in which the loss of luminous flux of the LEDs amounts to 30% when used under precisely defined ambient conditions (the L70 value), and therefore only has little to do with the service life of the product, which consists of substantially more components!

A critical component that can have much greater influence on the lifetime of the product is the power supply unit or driver electronics. The electronic components of these units are subject to the same deterioration process as all electronic parts, but a failure of the power supply unit means total failure of the entire lamp. It is safe to assume that the power supply unit will require replacing at least once during the lifetime of a bulb, and for luminaires with poor thermal management more frequent replacement may be necessary. With all LED luminaires this can be carried out with varying effort. Helecta retrofit bulbs are currently the only model known to us with retrofit technology that allows the power supply unit to easily be replaced, enabling the service life to be extended.

2) Maintenance
Conventional bulbs - mercury vapour or sodium lamps - are replaced on average every 4 years because they have either completely failed or no longer give off enough light. After 4 years, i.e. around 16,000 operating hours, the loss in luminous flux in LEDs with good thermal management is in the region of 5-10%, which is still far in advance of the maintenance interval. Nevertheless, there may be reasons to replace the LEDs, as their efficiency (in lm/watt) will still be increased significantly in the coming years. Current LEDs provide around 130 lumens/watts - a value that is expected to double in the years ahead. This means that local authorities which today install complete LED lights (heads) will, in a few years’ time, have to consider upgrading to the LED modules that will then be available, in order to continue to fulfil their duty to provide lighting with maximum efficiency and cost-effectiveness. There are still LED lights on offer where this retrofitting option is not available at all. However, many manufacturers are providing for this option by means of a modular structure for their LEDs. In the case of complete lamps it is therefore essential to ensure that both the power supply units and the LED modules can be replaced easily and inexpensively. As mentioned under 1), the power supply unit can also easily be exchanged in Helecta retrofit bulbs. Replacing the LEDs is not possible for design reasons, but also makes little economic sense. It must be remembered that a complete Helecta LED retrofit bulb costs more or less the same as an LED module for an LED lamp.

3) Energy efficiency
Energy efficiency means not only lower power consumption, but ultimately how much light you receive on the road, path or square for the input energy. Due to optimised optics or specially arranged LEDs, complete LED luminaires have an advantage over LED retrofit bulbs in this regard. These retrofit bulbs are designed for universal use and are not optimised for a particular lamp or specific application. The actual degree of efficiency of an LED retrofit bulb is therefore significantly affected by the type of lamp in which it is used. Measurements with various types of luminaires have shown that it is very often possible to substitute 50-80 W mercury vapour lamps with our HE-ST-16, and 80-125 W mercury vapour lamps with our HE-ST-20 version. The measured illuminance levels compared with the HQL bulb were consistently higher with mushroom or bell luminaires than with case luminaires.

4) Cost-effectiveness and future proofing
An LED retrofit bulb is priced at approximately ¼ of the cost of an LED lamp. Yet the energy savings compared with complete LED lights are similar. This means that the payback time is also only ¼ of that of complete LED lamps. In addition to comparatively low investments and the associated short payback periods, future proofing is another aspect that speaks in favour of retrofits. By using standard bases - E27 or E40 - it is always possible to change to the most efficient LEDs available at the time, without costly conversion. Even if the drivers and LED modules can be serviced or replaced in the lights of many manufacturers, this conversion involves another investment that may not be insignificant, and, depending on the manufacturer, also considerable effort. LED retrofit bulbs with their standard base, on the other hand, can easily be replaced with the latest generation of bulbs in case of a maintenance issue.

5) Performance
Here we come to the limits of retrofit technology. As described under section 1), high temperatures are "toxic" for the lifetime of LEDs and driver electronics. With LED light heads, the entire lamp housing can be used as a heat sink, whereas in the case of retrofitting the cooling surface is limited to the small size of the bulb. In order to achieve a cost-effective service life of many years, the power must be limited. Today, the limit for retrofitting is around 30 W. Bulbs with higher output levels and passive cooling get too hot, both on the surface (Light-Emitting Diodes) and on the inside (drivers), and deteriorate very quickly. This means that it is realistically possible to use an LED retrofit as a replacement for mercury vapour lamps up to 125 W, and in exceptional cases up to 150 W, depending on the type of lamp. Above that, only complete LED lamps with higher performance and a corresponding cooling surface can be considered.

6) Summary
There are various scenarios that speak in favour of the one or other solution. In the case of high output levels that have to be replaced, or lights which are already beginning to fail, or for stylistic reasons, there is a strong argument for using complete lamps. Retrofit bulbs are often the more sensible alternative when the maximum available power is adequate and the existing luminaire heads still have sufficient remaining service life. Ultimately, a decision must be taken as to which scenario is the best in economic terms; technically, neither of the two should be excluded.