Categories Lighting

LED Optics – Beam Angle Counts for Warehouse Aisle Lights Now More than Ever

An ongoing trend for Distribution Centers and Warehouses across the storage market is narrower aisles and higher ceilings.  The driver for the trend is about revenue per square foot. Owners and operators have the ability to store and sell more products if they pack in those products to areas that occupy less of a footprint.

This trend creates opportunities for the LED market to support the storage businesses at new levels. Old technology like metal halide fixtures distribute light to the sides as well as down. Fluorescent tube fixtures typically do the same. These “WIDE” beam angle fixtures waste a lot of the light in areas where it is not needed. Reflector kits on multi-tube T8 or T5 fixtures help reduce the wasted light going up and to the sides but they largely still deliver “WIDE” output.

Optics help LED high bay fixtures deliver “NARROW” beam angles. Look for LED high bay fixtures that maximize the light output with optics to direct the light where you need it most.  Save money by wasting less energy and review fixture costs relative to useable output.


High Bay Performance: Watts, Lumens, and Foot Candles
A Metal Halide High Bay with a 400 watt bulb (up to 450 watts with the ballast factor) may deliver 36,000 lumens of which only 24,000 are directional. The foot candles on a ceiling with 25’ x 25’ grid may come in at about 30 fc.

A Fluorescent High Bay with 6 Tube High Output (HO) T5 tubes at 54 watts each (total 324 watts) and a reflector kit may deliver 24,000 directional lumens and the 30 fc to replace the Metal Halide High Bays.

An LED High Bay without reflectors or optics at 216 watts may deliver the 24,000 directional lumens and the 30 fc to replace the Metal Halide and the Fluorescent High Bays.

An LED High Bay with reflectors may only needs 162 watts to deliver 18,000 “narrow focused” directional lumens to achieve the same 30 fc.

An LED High Bay with optics may only needs to draw 108 watts to deliver 12,000 “ultra-narrow focused” directional lumens to achieve the same 30 fc.

The key here is for buyers to understand that they should not just shop for high bays based on lumens. Buyers should definitely not disqualify LED high bays that have less lumens without looking into the reflectors and optics. The economic impact is significant as the wattage consumption decreases with more advanced technology:

  • 450 watt Metal Halide
  • 324 watt Fluorescent
  • 216 watt LED
  • 162 watt LED with Reflectors
  • 108 watt LED with Optics


The level of optics is determined by the ceiling height, the width of the aisles, and the foot candle needs at the floor and at the racks.


Understanding the loading process for fork lifts helps provide perspective on the width of the aisles:

  • Wide Aisle (WA) lift trucks operate in aisles that are 12’ on average. They are the standard counterbalanced lift trucks that have become synonymous with the term “fork lift”. Wide aisle trucks generally operate in aisles greater than 11’ for handling 48” deep loads.
  • Narrow Aisle (NA) lift trucks operate in aisles 8’ to 10’ across. This is primarily the domain of the stand-up reach and double-deep reach trucks.
  • Very Narrow Aisle (VNA) trucks generally operate in aisles of less than 6’ and often use guidance systems (wire, rail, optical) to travel within the aisles. Standardized VNA vehicles consist of man-up order selectors used to manually handle less-than-pallet-load quantities and man-up turret trucks used to handle unit loads.

Top Tip on LED Light Matching with Photometrics:
Choose a commercial LED lighting manufacturer or solutions provider that has high bay and /or aisle light fixtures with options for optics to focus the light down to where you need it most. Check the foot candle output at the horizontal work surface and on the vertical storage racks so that lift operators can see the products clearly. Overall, go beyond selecting a short list of fixtures by lumens or lumens per watt and look into the foot candles per watt and also the foot candles per dollar for the fixture cost.

Categories LED

Tipping Points, Toothaches and LEDs (?)

Scene 1: A toothache had me sitting in a comfortable endodontist’s chair, surrounded by state-of-the-art dental equipment. The smell of paint and new carpeting, in addition to soothing music, was in the air, and the lighting quality was both very good and comfortable. To avoid thinking about a possible root canal, I distracted myself by listing what I thought was lighting the space without looking up. I started noting my observations in my head. CCT was warm (probably 3,000 K), very good CRI (probably 90+), high R9 (good skin tones, certainly positive, maybe by a lot), high scalloped shadows on the wall (several “smaller” fixtures?), well-blended lighting on the walls a couple of feet below the ceiling line (not CFLs, probably linear sources), very uniform light at work surface heights throughout the entire space, no intense glare sources showed in the highly reflective equipment surfaces (definitely not CFL). I could hear someone coming so I quickly wrapped up my lighting audit. I guessed the room was lit with 3,000 K T5 fluorescent lamps in quite a few good volumetric lighting fixtures, possibly 4-foot but probably shorter, and probably not HO.

Scene 2: After explaining the need for an immediate root canal and readying the appropriate tools and supplies, the soft-spoken endodontist said, and with way too much enthusiasm, “We have reached the tipping point!” as I was reclined into position. From my new vantage point, to my surprise, I could clearly see 2 by 2, two-lamp, U-lamp, T12 fluorescent lamps and fixtures. I didn’t see that coming.

Scene 3: Prognosticators have recently said that the “LED tipping point” is behind us; therefore, why isn’t this newly-equipped, recently-renovated, state-of-the-art office lit with LEDs? Many likely think the explanation is complex, but I think it is pretty simple. Prognosticators come and go, but “lighting” evolves.

Scene 4: “Lighting technology” is mostly important to “technologists,” whereas, a reliable, cost-effective and comfortably-lit space is what is important to the customer. LEDs are a light source technology and not a lighting product or solution. LEDs can and will enable reliable, cost-effective and comfortably-lit spaces, but that won’t happen overnight. Have we forgotten the trials, tribulations and time it took to “evolve” from T12 to T8, from magnetic to electronic ballasts, or from T8 to T5?

Conclusion: Comparing that which comprised the fluorescent “evolution” of the past 30 years to the “evolution” awaiting us in/with solid state lighting is simultaneously exciting and sobering to those who understand the potential benefits, business opportunities, added functionality and challenges which might come along with solid state lighting.  I look forward to the day when my house recognizes my approach and turns on my porch light to minimize my key fumbling, when sensors recognize me beginning to sit in my favorite chair and turn on my reading lamp to a high intensity/warm color, and when those same sensors recognize me dozing and dim that reading lamp to a much lower intensity. I am excited about a future where concepts like this surround us in the workplace. Although I wouldn’t classify most consumers and users as “technologists,” it is clear to me that most can be aggressive consumers of “technology” with smart phones, tablet computing devices and cars that parallel-park themselves being only a few examples. The work will be challenging, but interesting. The benefits will initially be difficult to document with numbers, but nonetheless evident. Patience (by all) will be required but exciting times and opportunities lie ahead for lighting that leads.

Categories Lighting

Smart Lighting – Removing the Power Burden

Smart Lighting – One of the major benefits of solid-state lighting (SSL) is that it is very controllable. The advent of highly responsive LED lamps and an increasing ability to control brightness and color are giving rise to an imaginative new era in lighting design. The spectrum of innovation today includes context-aware lighting, lighting that reacts to user activity, and smart lighting systems that adjust to human requirements. The aim of these new lighting regimes is to increase productivity. But before implementing such a system, productivity benefits must be weighed against the cost of complex control systems and computing engines as well as the ability to manage power. SSL was first introduced with the goal of reducing power consumption and this remains central to the realization of the concept. Unless designers adeptly manage the power budget, any gains of these new systems could be wiped out.

Context-Aware Lighting – One type of leading-edge lighting system today takes account of user activity within a room and is known as context-aware lighting. Room occupancy sensing is not a new idea, but the increase in sophistication has taken the concept way beyond a motion-activated, on-off switch. With today’s technology, a lighting system can detect the presence of multiple occupants in a room and use their relative positions to deduce what the group is doing (eg., watching a presentation, drawing on a white-board, or simply working on a computer). The lighting system then provides lighting appropriate for that activity. This is certainly impressive, but does require significant computing power and numerous sensors that track the positions of multiple occupants continuously, and then infer their actions from their location and motion.

For this system to work acceptably for the room user(s), each of the sensor and lighting nodes must always be ready and react quickly to data inputs and commands and to provide data to the system – a delay of more than 500 ms is generally considered unacceptable for a lighting system to respond. Typically, a fast-wake from standby requires power to be continuously delivered to each node in the system. Therefore, controlling the amount of power consumed by smart lighting devices while they are inactive is very important if smart lighting is to deliver the power savings partly necessary to justify its expense.



Simple single-stage bulb driver



Simplified view of a multi-output-stage LED driver

Powering Smart Lighting Systems in Standby- SSL systems are typically powered by AC mains (either 115 VAC or 230 VAC) or, in some cases, using Power over Ethernet (PoE – IEEE802.3at and later derivatives under development).

Computer and telecom rack systems have standby power consumption in the order of 180 – 250 mW but are “network aware” with approximately 3 W of consumption. There will not be very many control hubs in the system so their power drain in quiet mode can typically be ignored.

Sensors and luminaires are another matter. A context-aware lighting system in an average sized conference room may use 20 motion sensors and 20 adjustable light sources. Even with a standby power consumption of 1 W per device this equipment will consume power equivalent to an incandescent bulb left permanently on – far from ideal if you are aiming to save power and reduce waste heat.

Therefore, deep sleep modes and power supplies that can efficiently deliver very low power will be necessary. The drive towards low power consumption in power adapters for cell phone chargers (currently less than 30 mW in no-load) means that it is now possible to keep power consumption low with existing low power drivers. LCD monitors in sleep mode consume approximately 100 mW while delivering 25-30 mW to control circuits that are able to monitor the PC interface looking for a wake-up signal.

Drivers that use less than 10 mW in standby mode are achievable (some are already in use in the TV and appliance market). Managing even the 40 nodes described above could therefore consume less than 0.5 W if the sensors can run in a zero-load mode.


Ultra-low, no-load/standby power supply


The LED lighting market has always had separate commercial/industrial and consumer requirements. Consumers need low cost and fast payback from LED bulbs and small luminaries. Commercial customers can take a longer term view, trading increased fixture cost for large luminaires against increased efficiency and reduced maintenance cost. It is therefore not hard to see that smart lighting will first see significant deployment in commercial applications where the increased infrastructure cost can be more easily accepted.  Care must be taken to limit standby power consumption in each power stage, lest the advantages of high efficiency are allowed to literally leak-away via many devices and sensors waiting in standby mode.

Categories Bulb

Latest 60 W Equivalent LED A19 Bulb for $2.49

For a limited time, one major local home improvement retailer in the United States is offering a non-dimming 60 W equivalent LED A19 type bulb for $2.49 each, sold in a two bulb value pack manufactured by a major LED maker. Similar types of bulbs were about 6x the cost a few years ago. With price drops like this, we tend to see articles and discussions about the fall in LED bulb prices over the past few years, performance comparisons to previous versions on lumens/watt trends, or teardowns and investigations into the cost of materials etc. I decided to do a teardown to look at the design changes that went into this bulb to drive down cost versus an LED bulb from just a few years ago.   The trends to note from this perspective have been ongoing, but then the question to ask ourselves as designers is where will the basic design of an LED bulb step to next?

Figure 1 is a picture of the $2.49 bulb and as you can tell I was not trying to be pretty about the heat sink and casing as I was more interested in the driver at first.  It requires 8.5 W for a 60 W equivalent at 800 Lumens A19 bulb.


Figure 1. $2.49 A19 60 W Equivalent LED Bulb


Figure 2. Older A19 60 W Equivalent LED Bulb for comparison


Figure 2 shows the teardown from a bulb taken apart a few years ago, it cost $15.99 but I promised not to get into a LED pricing reduction analysis.  By the way, it required 8 W for only a 40 W equivalent at 450 Lumens A19 bulb.

To begin with, removing the plastic “optics” used to require a heat gun, but now days most of the time you can pry the plastic cover from the heat sink base.  Then simply remove a few screws and release the driver inside the casing. In older bulbs, there was still potting material inside the casing surrounding the driver along with a series of interlocks holding the casing to the heat sink.  Potting material is still used today, but I am considering general trends in the construction of LED bulbs.  The new bulb weighs around 49 g total, the old bulb heat sink alone is 70 g so for the same input power to the bulb, the heat sink is smaller and there is no potting around the driver. The number of LEDs went from 18 to 11 with the lumen output almost double. I did not measure the LED voltage on the old string, but I measured over the 60 V SELV limit on the new bulb as safety is now achieved from the mechanical housing not through electrical isolation from the driver.  Therefore, it’s obvious that lower weight, less LED counts, better materials or materials that function good enough can all contribute to lower cost.

The driver is more interesting.  The old driver was an isolated flyback design.  The controller has power factor correction, but what is not shown in Figure 2 is the added expense of having to cut the printed circuit board along the primary to secondary isolation boundary for safety creepage and clearance. The new driver is non-isolated and does not use a controller, but a set of discrete components.  The new driver has a smaller EMI filter and even the transformer is smaller. The BOM count was 53 or so in the past versus 27 or so today – this will reduce cost and improve reliability in the driver. [1]

Clearly, the trend is to reduce the driver electronics besides the material changes and efficiency of LEDs.  So where are drivers for LED bulbs going next?  Integration: but there are discrete designs that use the low cost components without the need for an integrated analog controller that provides good enough performance. NPN transistors in place of MOSFET transistors, better EMI filtering, fuses part of the printed circuit board, etc.  Non-isolated designs: when thinking about this trend and reducing component count the idea of Direct AC LED topologies can reduce the component count further and possibly eliminate some of the lower reliability electrolytic capacitors.

But how do these observations enable a smart LED solution?  Lighting is evolving from something used to see or read, but is becoming a user experience: warm dimming, color tuning, communication to control, visible light communication to guide us, sensors that interpret implicit human movement or environment changes, etc.  The latest low cost LED Bulb is a pathway to enable the technologies to take lighting into the future by reducing not just cost, but by pushing the boundaries on how we think about the construction of the bulb and how we challenge conventional thinking about consumer electronic design.  As a semiconductor supplier, the need is to stay ahead of the curve by providing the building blocks to make these future lighting applications realized, how many suppliers are there that can provide these building blocks? I know of one that is developing the building blocks to advance lighting into the smart future. [2]

Categories LED

Driving an LED Load

In this month’s article, we address factors that influence how an LED is driven, including different driver techniques and why they are preferred for a variety of lighting applications. We look at the effects of different loads, as well as control options to drive LED loads effectively.

Constant Current or Constant Voltage?
LEDs typically require a constant current rather than a constant voltage to operate. The LEDs themselves present a constant voltage drop across the line (although the actual value of the voltage drop varies between approximately 3.2 V and 3.0 V depending on LED type and temperature).

Constant current drivers (CC) deliver a constant current to the load across a range of LED voltage conditions. For bulbs, the driver is typically designed to deliver constant current across a narrow LED voltage range (perhaps nominal voltage +/- 10 percent). These drivers are very effective in tightly specified designs (such as LED bulbs), making them application specific. However, this approach requires the design of a dedicated CC power supply.

Another approach is to use a driver that can deliver a constant voltage (CV) across a wide current range. Many CV drivers are fully isolated, simplifying the design process and removing much of the burden of meeting safety approvals, it also facilitates scalability  by adding more parallel LED strings.

In order to maintain a constant current through the LED string with a CV output (such is often delivered from ballast-type drivers), a series resistor is added, the value for which is determined by the equation:

where VDC is the nominal output voltage from the power supply, VLED is the voltage drop across the whole LED string and ILED is the desired LED forward current.

This is a very simple relationship, but the effect of circuit tolerances becomes significant. Output voltage ripple and the voltage tolerance of the driver result in dramatically increased effects in LED circuits compared to similar low-voltage drivers used for more conventional power applications.  For example, although a voltage variation of  +/- 5 percent is not large when considering the output voltage, in an LED driver with a load resistor, ILED varies according to the amount of change in the difference between driver voltage and the LED voltage – the effect on output current is magnified.

In order to achieve an acceptable design, the engineer must trade off power dissipation in the resistor against output current variation.

The human eye is relatively insensitive to light intensity and adjacent drivers subject to similar input voltage and ambient conditions tend to track each other (the difference between drivers in the same conditions will be less than the worst case described above). Therefore, in fixed or consistent conditions the effect of the tolerance in a CV LED driver may not be a major concern, provided that output voltage can be controlled within a relatively narrow range.

Primary and Secondary Control – Performance vs. Cost
To drive an LED load effectively with a CV driver, output regulation must be well controlled. Secondary side controllers that directly measure output voltage and deliver correcting information to the primary side switching stage will tightly control the output but will also add cost and shorten product lifetime (the opto-isolator, which is used to transfer information from secondary to primary, degrades over time).

In contrast, primary-side controllers do not directly monitor the output stage. Instead, they infer output performance using indirect means. A challenge with this approach is that component variation can affect output regulation. Leakage inductance in the isolation transformer can easily vary by ±15 percent in production, which will significantly degrade the output tolerance of a design.  In order to improve accuracy, primary side-controllers (such as LYTSwitch-2 LED driver ICs) use correction algorithms to compensate for inductance variation as well as line and load effects. Thus, they can achieve output regulation of better than 5 percent across line and load.


Figure 1. Load and line regulation in voltage mode for LYTSwitch-2 LED driver ICs.

The accuracy of primary side controllers with good line/load regulation coupled with the lower system cost and higher reliability of this approach results in wide utilizationfor low power drivers.

Combined CV/CC Drivers
By combining different control modes, it is possible for an LED driver to have both constant current across a variable voltage and constant voltage across a variable current.  The benefit of this technology is that the same control IC and power supply circuitry can be used for a wide range of applications and load conditions. The CC mode allows the output to deliver constant current across a wide output voltage swing (typically 2:1 or better) as well as a wide output voltage range.


Figure 2. Combining different control modes – LYTSwitch-2 LED driver IC with constant current across a variable voltage and constant voltage across a variable current.

Using On-Off control for CV operation and Variable Frequency Control for CC portions of the regulation curve results in a product that can support both CC direct LED driver and CV applications.

This approach is particularly useful for power supply manufacturers who wish to support a wide range of customer applications with a limited range of power supplies.

As we have discussed, an LED requires constant current, and can be driven using different power supply types. So far we have considered the LED load to be a string of ideal diodes which all behave the same. In the next article we will consider the effects of variations in LED characteristics and how they affect efficacy, output ripple and other circuit performance metrics; this will clearly demonstrate that it is not possible to determine circuit performance without a clear understanding of the nature of the LEDs which will be used.