Most lighting decisions on a project are made on a datasheet, not a showroom floor. Understanding what is actually happening inside an LED makes those figures easier to read, and makes it far harder for a supplier to sell you a number that does not mean what you think it means.
The basic principle
An LED is a semiconductor, not a lamp in the traditional sense. Pass current across a junction of two doped materials and electrons drop into holes on the other side, releasing the difference in energy as photons. That effect is called electroluminescence, and the energy gap of the semiconductor determines the colour of the light produced.
This matters practically for two reasons. First, an LED produces light in a narrow band, so white light has to be manufactured, usually by coating a blue emitter with phosphor. Second, there is no filament to burn out. LEDs do not fail in the way incandescent lamps fail – they dim, gradually, and how gracefully they do that is one of the most useful things on a datasheet.
Reading lumen maintenance: L, B and F ratings
Because LEDs fade rather than fail, “lifespan” on its own is close to meaningless. What matters is the L rating.
- L70 at 50 000 hours means that after 50 000 hours, the luminaire is still producing at least 70% of its original output.
- L80 or L90 at the same hours is a considerably better product – it has faded less over the same period.
- The B rating tells you what proportion of units are allowed to fall below that figure. B50 means half of them may.
- The F rating covers outright failures.
A luminaire quoted at “50 000 hours” with no L figure attached is not telling you anything you can design around. Ask for the full rating.
Efficacy is the number that governs running cost
Efficacy – lumens per watt – is how much useful light you get for the electricity you pay for. It is the single figure that most directly drives operating cost over the life of an installation.
Two cautions when comparing. Some manufacturers quote chip efficacy rather than luminaire efficacy. Chip efficacy ignores losses in the driver, the optic and the diffuser, and can overstate real performance by a wide margin. Always compare delivered lumens from the complete luminaire. Second, efficacy falls as colour rendering rises and as colour temperature warms – a 3000K high-CRI product will read lower than a 6500K low-CRI one, and that does not make it worse.
Colour temperature and colour rendering are not the same thing
Correlated colour temperature (CCT), measured in kelvin, describes the appearance of the light: 3000K is warm, 4000K neutral, 6500K a cool daylight white. It says nothing about quality.
Colour rendering index (CRI) describes how accurately colours appear under that light against a reference source. CRI 80 is the general commercial minimum. Retail, healthcare, and anywhere colour judgement matters should be specified at CRI 90 or above. Two products can both be 4000K and look completely different in a paint aisle.
Many current products are CCT-selectable, with a switch that sets 3000K, 4000K or 6500K at installation. On a project where the final specification is still moving, that removes a decision from the critical path and reduces the number of variants to hold.
The driver is what usually fails
The LEDs themselves rarely fail first. The driver does. It converts mains supply to the constant current or constant voltage the array needs, and it is the component most exposed to whatever the local grid is doing.
In South African conditions this deserves particular attention. Specify surge protection appropriate to the site – 10kV or 20kV on exposed outdoor and industrial installations is not excessive. Check the input voltage range: a driver rated AC100-305V will tolerate far more than one rated AC220-240V. Where lighting runs on a generator or an inverter during load-shedding, confirm the driver tolerates the waveform.
Size drivers with headroom rather than to the exact load. A driver run permanently at its ceiling runs hot, and heat is what shortens its life.
Thermal management determines whether the numbers hold
An LED converts a meaningful share of its input power to heat, and that heat has to leave through the body of the fitting. This is why housing material and heatsink design are not cosmetic details. A well-made die-cast aluminium luminaire will hold its output far longer than a sealed plastic one with the same chip.
It is also why a fitting’s stated lifespan assumes an ambient temperature. A luminaire rated at 25 degrees ambient in a warehouse roof space that reaches 45 will not achieve its quoted figure. Check the operating temperature range against the actual installation.
Dimming: confirm the protocol, not just the word
“Dimmable” on its own is not a specification. The protocol matters, and mismatches are a common cause of flicker and of fittings that will not dim below a certain point.
- 0-10V and 1-10V are analogue controls, common in commercial installations. They are not interchangeable – a 1-10V driver will not switch fully off on a 0-10V signal.
- DALI is addressable and digital, which suits larger installations where zones and scenes may be reconfigured later.
- TRIAC (mains dimming) is common in residential work but needs the driver and dimmer to be matched and tested together.
- PWM switches rapidly rather than reducing current. Check the frequency where cameras are in use.
Ingress and impact ratings
The IP rating has two digits: the first for solids, the second for water. IP65 is protected against dust and low-pressure jets, which covers most outdoor use. IP66 handles powerful jets. IP67 tolerates temporary immersion, and IP68 continuous immersion.
Coastal installations deserve more thought than the IP number alone. Salt-laden air attacks aluminium and fixings, so specify marine-grade finishes and stainless fasteners along the KwaZulu-Natal and Western Cape coasts regardless of the IP rating.
IK ratings cover impact resistance, and matter wherever a fitting is reachable – car parks, walkways, sports facilities and schools.
Glare, and why UGR belongs on the specification
Unified glare rating quantifies discomfort glare. Below 19 is the usual target for offices and anywhere screens are used; below 22 is acceptable for general interiors. It is one of the most commonly omitted figures on a quotation and one of the most common causes of complaints after handover.
A practical specification checklist
- Delivered lumens from the complete luminaire, not the chip
- Efficacy at the specified CCT and CRI
- L, B and F ratings with the hours they refer to
- Driver make, input voltage range and surge protection level
- Dimming protocol, stated exactly
- IP and IK ratings against the real installation conditions
- Operating ambient temperature range
- UGR where people work under it
- Warranty terms, and what they actually cover
- Certification – EMC, LOA, IEC and RoHS as applicable
Every Mesmerize product page carries these figures in full, with the datasheet attached. If a specification you need is not shown, our technical team can supply it – get in touch and tell us about the project.
