To understand why LED lights are heavier than traditional high pressure sodium (HPS) or metal halide fittings we have to look into the way these sources create their light. Traditional forms of lighting used one of two standard forms of generating the light – Incandescent or HID. Whilst HID lamps are not regarded as ‘efficient’ from an energy usage point of view, when it comes to big field or sport applications they are hard to beat. Whilst many smaller work light applications had long since migrated to LED, sports fields hung on to the HID’s for one simple reason – LED did not work very well. However, by 2018 the LED’s had advanced enough to be a serious contender but it still required a lot of heat sinking and surface area to cope with the heat generated from 1500W of hard-working LED’s.
An incandescent light bulb, incandescent lamp or incandescent light globe is an electric light with a wire filament heated until it glows. The filament is enclosed in a bulb to protect the filament from oxidation. Current is supplied to the filament by terminals or wires embedded in the glass. Wikipedia
Incandescent lamps use a filament which is essentially a resistor. The electricity passes through the filament and due to the increased resistance the wire gets very hot and glows. If this was in the open air the filament would oxidise and quickly burn up. However, the bulb is a vacuum which just allows the filament to glow brightly, creating the light.
High-intensity discharge lamps are a type of electrical gas-discharge lamp which produces light by means of an electric arc between tungsten electrodes housed inside a translucent or transparent fused quartz or fused alumina arc tube. Wikipedia
By contrast, HID bulbs are filled with gas. When the lamp is turned on the bulb causes an arc within the bulb, fluorescing the gas which in turn generates light. Both of these forms of lighting generate heat, incandescent significantly more than HID. This heat is generated forwards, or through the front lens. If you hold your hand in front of a halogen lamp you can feel the heat generated. This means that the protective screen on the front of these lamps needs to be a heat resistant material, often glass. This not only gives good transparency but also can stand up to the heat. The most important part therefore was allowing heat to escape from the front. The main body of the lamp was just thin galvanised plate capable of holding the electronic ballast, bracket etc. This could be quite aerodynamic as it was filling no purpose other than protecting the internals from rain and dusty.
A light-emitting diode is a semiconductor light source that emits light when current flows through it. Electrons in the semiconductor recombine with electron holes, releasing energy in the form of photons. Wikipedia
Compared to these traditional forms of lighting LEDs work in a very different way. When an LED is turned on, light is emitted from the front but all the heat goes back down into the PC board. Overheating of LED’s causing very rapid failure therefore that heat has to either be controlled or removed. This results in the use of ‘heat sinks’ as a way of removing the heat and dissipating it away from the temperature-sensitive LED’s. The higher the wattage of the lamp, the more heat sinking is required and the larger and heavier the lamp becomes. Static LED lamps generate significant heat and with very hot evenings being common, nothing can be left to chance. A light breeze reduces the heat dramatically but this cannot always be relied on. There is also the possibility that the lights may inadvertently be left on during the day. All these factors have to be considered in the initial housing design of the lamps.
The material of choice so far has been aluminium. It has very good heat transfer properties, is reasonably priced and much lighter than most other metals. The other major factor it is easy to extrude, mould or shape to whatever is needed for a specific lamp with extruding and die-casting being the most common methods. Other material options have been toyed with over the years, like graphene, along with other polymers, however the heat sink-to-weight ratio doesn’t justify moving away from aluminium in the foreseeable future for high power LED’s like those used in sport applications. So, in conclusion, there doesn’t seem any short term answer to this issue of seemingly over-heavy LED lights. For the next few years at least we will be constrained in what we can do by way of retro-fitting metal halide or sodium vapour lights based on the weight and sail area. However, don’t overlook this possibility completely as if you get an engineers report its likely there is some tolerance there which just may be enough to allow for the LED upgrade your club has been longing for for many years.
