LED & Drive Parameters
LED Type
Forward Current I_f350 mA
Forward Voltage V_f (25°C)3.20 V
WPE @ 350mA (25°C)45.0 %
Standard Flux Φ₀120.0 lm
θ_j-s (LED Package)5.0 K/W
θ_s-a (Heat Sink)3.0 K/W
Ambient Temperature T_a25 °C
Flux Temp. Coeff. δΦ/ΔT-0.50 %/°C
V_f Temp. Coeff. dV/dT-2.0 mV/°C
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T_j Junction Temp. [°C]
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Operating Flux Φ [lm]
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Efficacy [lm/W]
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Input Power P_in [W]
Drive Current vs Flux & Efficacy
Junction Temperature vs Flux Maintenance
Flux Bin Reference Table (ANSI/IES)
| Bin | Flux Range (lm) | Typical Application | Current Design |
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LED Thermal & Optical Design Theory
Input power and optical energy:
$$P_{in} = V_f \cdot I_f, \quad P_{opt} = \eta_{WPE} \cdot P_{in}$$Heat generation and thermal resistance:
$$P_{heat} = P_{in}(1 - \eta_{WPE}), \quad T_j = T_a + P_{heat} \cdot (\theta_{j\text{-}s} + \theta_{s\text{-}a})$$Temperature-corrected luminous flux:
$$\Phi(T_j) = \Phi_0 \cdot \left[1 + \delta_\Phi \cdot (T_j - 25)\right]$$Luminous efficacy:
$$\eta_{lm/W} = \frac{\Phi(T_j)}{P_{in}}$$
Thermal Design Note: In practice, LED T_j is often estimated from thermocouple measurements at the solder point (T_solder) or board (T_board), making θ_j-s accuracy critical. The L70 lifetime defined by IES TM-21 (time for flux to reach 70% of initial) is strongly dependent on T_j — every 10°C increase in T_j roughly halves L70 life. ANSI/IES flux bin standards are essential for consistency across production lots.