The Recessed Lighting Calculator and Recessed Lighting Spacing Calculator eliminate fixture layout guesswork, the Lumens to Watts and Watts to Lux calculators let you compare bulbs on equal footing, and the 15-Year Incandescent vs CFL vs LED Running Cost Comparison shows exactly what switching saves. Growers can also use the Daily Light Integral Calculator to hit precise plant lighting targets.
Browse the full list — ordered by how often other users open each tool — or open the Trending tab for what's popular right now. Every calculator is free, requires no account, and works on any device.
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LED Strip Power Supply CalculatorCalculate the right LED strip power supply (PSU) wattage and current. Enter watts per meter, length and voltage to size a driver with safety headroom.
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Lumens per Square Foot CalculatorCalculate foot-candles (lumens per square foot) from total lumens and room area. Free lighting calculator with instant lux conversion.
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LED Equivalent Wattage CalculatorConvert incandescent bulb wattage to its equivalent LED wattage. Estimate lumens, LED power draw, and energy savings using bulb efficacy.
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Inverse Square Law Light Intensity CalculatorCalculate light intensity at a new distance using the inverse square law E₂ = E₁ × (d₁/d₂)². Free physics & lighting tool for lux and illuminance.
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LED vs Incandescent Bulb Savings CalculatorCalculate how much money and electricity you save each year by switching from incandescent bulbs to LEDs based on wattage, usage hours and energy price.
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LED Strip Length, LED Count & Power Draw CalculatorCalculate LED strip power draw, total LED count and current. Enter strip length, LEDs per meter, watts per LED and voltage to size your power supply.
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Lumens Needed CalculatorCalculate how many lumens you need to light a room. Multiply floor area (m²) by the recommended lux level to get total lumens for any space.
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LED Wire Voltage Drop CalculatorCalculate the voltage drop in wires feeding an LED or LED strip. Enter current, length, wire area and material to find loss, voltage at the LED and power waste.
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Christmas String Light Count CalculatorFind how many Christmas string lights you need to cover a given length and the total wattage they draw. Quick holiday lighting planner.
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LED Payback Period CalculatorCalculate how fast an LED bulb pays for itself. Enter wattages, usage hours and electricity rate to see annual savings and payback in years.
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LED Bulb Lifespan CalculatorConvert an LED bulb's rated lifespan in hours into years based on daily usage. Find out how long your LED bulbs will really last.
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Average Illuminance CalculatorCalculate average illuminance (lux) from light fixtures using the lumen method: fixtures, lumens, coefficient of utilization, light loss factor and area.
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Lumens Needed CalculatorCalculate how many lumens you need to light a room. Multiply floor area (m²) by the recommended lux level to get total lumens for any space.
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Lux to Lumens CalculatorConvert lux to lumens instantly. Multiply illuminance (lux) by the illuminated area in square metres to get total luminous flux in lumens.
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Room Lighting Lumens CalculatorCalculate how many lumens a room needs based on its size and lighting purpose. Enter length, width, and light level to get total lumens and bulb count.
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Lumens to Lux CalculatorConvert lumens to lux instantly. Enter luminous flux (lm) and the illuminated area in m² to find illuminance (lux = lumens ÷ area).
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Watts to Lumens CalculatorConvert watts to lumens instantly. Enter power in watts and luminous efficacy (lm/W) to find the light output in lumens for LED, CFL or incandescent bulbs.
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Light Bulb Energy Cost CalculatorCalculate the yearly, monthly and daily electricity cost of running a light bulb from its wattage, hours used per day and your price per kWh.
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LED Strip Power Supply CalculatorCalculate the right LED strip power supply (PSU) wattage and current. Enter watts per meter, length and voltage to size a driver with safety headroom.
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Lumens per Square Foot CalculatorCalculate foot-candles (lumens per square foot) from total lumens and room area. Free lighting calculator with instant lux conversion.
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LED Equivalent Wattage CalculatorConvert incandescent bulb wattage to its equivalent LED wattage. Estimate lumens, LED power draw, and energy savings using bulb efficacy.
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Inverse Square Law Light Intensity CalculatorCalculate light intensity at a new distance using the inverse square law E₂ = E₁ × (d₁/d₂)². Free physics & lighting tool for lux and illuminance.
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LED vs Incandescent Bulb Savings CalculatorCalculate how much money and electricity you save each year by switching from incandescent bulbs to LEDs based on wattage, usage hours and energy price.
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LED Strip Length, LED Count & Power Draw CalculatorCalculate LED strip power draw, total LED count and current. Enter strip length, LEDs per meter, watts per LED and voltage to size your power supply.
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Candela to Lumens CalculatorConvert candela (cd) to lumens (lm) using luminous intensity and beam apex angle. Free, accurate candela-to-lumens converter with solid angle output.
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LED Payback Period CalculatorCalculate how fast an LED bulb pays for itself. Enter wattages, usage hours and electricity rate to see annual savings and payback in years.
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Lumens Needed CalculatorCalculate how many lumens you need to light a room. Multiply floor area (m²) by the recommended lux level to get total lumens for any space.
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Lux to Lumens CalculatorConvert lux to lumens instantly. Multiply illuminance (lux) by the illuminated area in square metres to get total luminous flux in lumens.
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Room Lighting Lumens CalculatorCalculate how many lumens a room needs based on its size and lighting purpose. Enter length, width, and light level to get total lumens and bulb count.
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Lumens to Lux CalculatorConvert lumens to lux instantly. Enter luminous flux (lm) and the illuminated area in m² to find illuminance (lux = lumens ÷ area).
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Watts to Lumens CalculatorConvert watts to lumens instantly. Enter power in watts and luminous efficacy (lm/W) to find the light output in lumens for LED, CFL or incandescent bulbs.
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Light Bulb Energy Cost CalculatorCalculate the yearly, monthly and daily electricity cost of running a light bulb from its wattage, hours used per day and your price per kWh.
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Coefficient of Utilization (Lumen Method) CalculatorCalculate how many light fixtures you need using the lumen method with coefficient of utilization (CU) and light loss factor (LLF).
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PPFD to DLI CalculatorConvert PPFD (µmol/m²/s) to DLI (mol/m²/day) using your grow light's intensity and daily photoperiod. Free, instant grow-light calculator.
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Lumens to Candela CalculatorConvert lumens to candela using the beam apex angle. Free lumens-to-candela calculator with solid angle output, formula, and a worked example.
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Luminous Efficacy CalculatorCalculate luminous efficacy in lumens per watt (lm/W) from a light source's luminous flux and electrical power. Fast, free, and accurate.
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LED Series-Parallel Array CalculatorCalculate the series resistor, voltage drops, current and power for an LED array with multiple parallel strings of LEDs in series.
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Watts to Lumens CalculatorConvert watts to lumens using luminous efficacy (lm/W). Compare LED, CFL and incandescent brightness instantly with this free calculator.
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Grow Light Coverage Area CalculatorCalculate how many square feet your grow light covers from its PPF output and your target PPFD. Free, instant grow tent coverage area calculator.
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Candela to Lux CalculatorConvert candela (cd) to lux (lx) using luminous intensity and distance. Free candela-to-lux calculator with the formula lux = cd / distance².
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Lumens Needed CalculatorCalculate how many lumens you need to light a room. Enter room size and type to get the total lumens required for proper, comfortable brightness.
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Lighting kWh Usage CalculatorCalculate the kWh energy used by your lighting and its cost. Enter bulbs, watts, hours per day and days to estimate consumption and electricity bills.
Frequently asked questions
What lighting problems can I solve with these calculators?
The collection covers room and fixture layout (spacing, quantity, and lumen output for recessed lighting), bulb comparison and energy savings, unit conversions between lumens, watts, lux, and foot-candles, LED upgrade cost analysis, and horticultural lighting planning via the Daily Light Integral Calculator.
How accurate are the spacing and energy savings results?
The calculators use standard illumination formulas and published bulb wattage data. Results are solid planning estimates. For safety- or code-critical lighting installations, verify your design against the relevant electrical and building codes and have a qualified electrician or lighting designer review the final plan before proceeding.
Is any data I enter stored or shared?
No. All calculations run entirely in your browser. Room dimensions, fixture counts, and energy cost figures you enter are never sent to or saved by our servers.
Which lighting calculators do people use most?
The Lumens to Watts Calculator and LED Savings Calculator are consistently the most visited, followed closely by the Recessed Lighting Calculator. The list is ranked by real-world usage, and the Trending tab highlights which tools are gaining traffic right now.
Are these tools free to use?
Completely free — no account, no subscription, no hidden charges. Open any calculator on your phone, tablet, or laptop and get your answer in seconds.
