LED lighting design on a budget
Simply choosing the cheapest LED components has its risks and a better approach is to take a system-level perspective, aiming for the most cost-effective design, writes Mark Pinkney, divisional marketing manager, Anglia Lighting
LED lighting continues to gain in popularity, but high initial purchase prices can be discouraging for some buyers.
Designers’ attention is turning to reducing cost in future generations of products. The right design and component selection can help significantly without degrading the desirable characteristics of LED lighting.
As a means of reducing cost, simply choosing the cheapest components risks delivering a poorer experience for end users. A better approach is to take a system-level perspective, aiming for the most cost-effective design that meets customers’ needs. This involves considering how each part of the system contributes to meeting targets such as total lumen output, quality of light, useful lifetime, and power consumption.
It can be tempting to focus predominantly on the LED emitters, as these are arguably the most exciting components. LED manufacturers continue to strive to offer devices that produce the greatest total flux and the highest efficacy (lumens per Watt).
The latest and best-performing technologies tend to have the best promotion and the most favourable pricing. It is worth noting here that choosing cheap LEDs from unknown or unproven sources is a false economy. Poor or inconsistent performance, as well as unreliable supply, can quickly tarnish brand reputation.
Designing a lamp with a small number of high-output LEDs will achieve a different overall lighting effect compared to using a larger number of lower-output emitters. It is important to consider the desired lighting effect and to balance the relative costs of such differing approaches.
It can be tough, however, to know how different LED types will perform in practice. Using datasheet performance figures to calculate the number of emitters needed to meet the overall lumen target can be misleading. Quoted figures do not tell the full story of how an LED is likely to perform in a particular application.
Working with a component distributor can provide valuable help to identify suitable devices. Sound advice from a trusted partner can help to focus the project onto a relatively small number of LEDs that are worthy of further evaluation.
Besides the important issue of LED selection, other aspects that significantly influence performance include the thermal design in particular as well as driver circuitry and optical design.
The thermal design of the lamp governs the maximum power that may be delivered to the LEDs in the fixture. Improving the thermal design can give greater freedom to choose the most cost-effective LEDs that will produce the required lumen output.
Over-specifying the thermal design, however, can increase the overall cost unnecessarily. Since the service lifetime of an LED is closely related to operating temperature, the heatsink needs to be sized appropriately to maintain the correct temperature, in the target environment, to achieve acceptable lamp life.
Electronic Design Considerations
Generally, producers of driver ICs have identified increased integration as an effective means of delivering competitively priced products.
Lighting designers can target the most highly integrated products – ultimately a single-chip driver solution with integrated power mosfets – to achieve cost down. The trade-off can be a loss of flexibility.
Using a driver plus discrete mosfets, and foregoing some of the economies offered by semiconductor integration, can help protect that flexibility.
High-voltage LEDs are an emerging technology that also offers the possibility to reduce the cost of solid-state lighting. LEDs capable of sustaining forward voltage up to around100V are now available, which allow lower drive currents and hence permit smaller, lower-cost components. The smaller components also allow drive electronics to be implemented on the same board as the LED for further cost savings.
The optical design, comprising any combination of reflectors, lenses or diffusers, can have a significant impact on the practical performance of the luminaire. Taking care to –maximise the light reaching the surface to be illuminated, rather than focusing purely on the raw light output of the fitting, can present opportunities to simplify the electronic design.
Producers of high-quality optics are now optimising their designs for particular LED emitters from well-known manufacturers. These can offer better performance, as well as easier fitting. Some optics are offered as arrays for use with two or more emitters. This can save parts costs, including the costs of mechanical fittings, and the assembly costs associated with fitting several discrete lenses to individual emitters.
Spreading Design Costs
LED-lighting initiatives such as Zhaga are aiming to standardise critical aspects of LED light engines. Although such industry-wide standards could take flexibility away from designers, the principle of standardisation can be applied usefully within a lighting manufacturer’s own product range. Creating a single PCB design that can be used within several products across a range can help to spread the costs of electronic design and development.
A common board design may provide pads for attaching the maximum number of LEDs and associated circuitry for the most powerful product in the range, while other variants can be built by partially populating the same PCB. LED manufacturers have been utilising this principle for some time, by offering families of products that share a common footprint and package technology while having different characteristics such as colour temperature or power rating.
Finally, when considering the question of the cost of an LED lighting product, it is worth considering its v alue to the customer. Despite intelligent, system-wise design to reduce cost, the selling price may still be higher than alternative products on the market. However, advantages such as lower energy costs compared to conventional incandescent fittings, or longer life and better performance compared to competing budget LED-based products can yield a more favourable overall cost of ownership; particularly in commercial or municipal applications, such as warehouse lighting or street lighting.
In some locations, such as large factories or roadways, replacing conventional lighting with LED technology can deliver a return within a matter of months.
When working towards a target price for a new design, it is vitally important not only to consider the system and the application, but also the expectations of the target market.